This seems to be a common problem. I've read a lot of the posts and tried most of the suggestions but have had no luck. I have a hot water heating system with two main pipes, one I assume is a supply pipe, the other a return. Each radiator in the house has one side connected to the supply pipe, the other to the return. The last radiator on the run has never really gotten hot, warm at best. I recently changed that old semi-recessed radiator and installed a baseboard type. I changed two others - all on the top floor of a split level house - and added one to the middle floor. Long story short - the last radiator now stays stone cold and one of the others I replaced is cold. The other replacement is hot as well as the new one I added. I put bleeder valves on all the rads I installed. I fast filled the system and bled all the valves. No luck. I raised the pressure to 20psi and bled the valves. Still no heat in those tworadiators. The pressure is now about 12 psi and there is no air coming out of the bleeders, just water.
Does it matter what size pipe I used off the main pipes to the radiators? The mains are 3/4" and I used the same size going to the rads, replacing the 3/8" that was on the old rads (the guy at home depot didn't believe they were 3/8" until I brought him a piece of one).
Of the two that are cold, one has a hot supply pipe running right up to it but the rad stays cold. The other one's supply gets cold about three feet before the elbow leading up to it.
Does it matter if the bleeder valve is on the supply side or the return side of the radiator? Would a bleeder on each side perhaps relieve a stubborn air pocket?
I know this is a long post but I wanted to give as much detail as I could. Thanks for any suggestions.

 

Pete, my first thought is that it's a flow problem. It would seem that most of the flow in your system is heading out the supply, through the first few rads, then back to the boiler. There is possibly little flow left at the end of the run.

If you are bleeding and getting only water, it may support this theory. There could of course still be an air pocket.

Are there valves on the rads to regulate the flow through each ? If so, try closing the early ones and see if you can force some flow to the later ones.

I'm wondering if the installer used the 3/8" pipe as an attempt to 'balance' the system ... providing a restriction at each rad to allow flow to the end.

There is a piping scheme called 'reverse return' that alleviates this problem. With reverse return, the LAST rad on the supply side is the FIRST rad to return. This keeps the distance the water travels through each radiator nearly the same, and it's much easier to balance that way. This isn't really a retro-fit job though, unless the return pipe is exposed in a basement.

You may also have a weak circulator... what circulator is on your system ?

How many rads are running on that 3/4" main ? That size pipe is good for about 40000 BTU of heat transfer. But even so, stone cold is not good. Even if the main is undersized, you should get _some_ heat in each... unless, again, you are running out of flow.

Back to the valves on the rads, hopefully you do have them, if you close the ones on the hot rads, and force water through the cold ones, you should be able to push any trapped air out and back to the boiler where it will be caught and expelled to either your expansion tank, or the auto air vent.

Can you take some pics and post them on www.photobucket.com (free) and post a link here ? Might help to see the piping ...

 

Thanks for replying.
Unfortunately there are no shut off valves on the rads.

There are 10 rads running on the main. The first 7 are hot. #8 has hot pipes leading up to it but is cold, #9 is hot and the pipes leading to and from #10 get cold about a foot after the "T" that leads to #9. This sounds odd to me because there is a hot rad between two cold ones, although the two cold ones are on the level above the main and the hot one is on the floor below it-don't know if that matters.

Most of the main is exposed as it runs around the ceiling in my den feeding the rads on the floor above and the three in the den. It also runs along my basement ceiling feeding the other rads on the main floor.

A reverse run system would be possible - if I'm getting the concept right. I guess I would cap the return pipe right before the boiler, then run a pipe from the the last rad's return side to the boiler, right?

Do you think running 1/2" pipe off the main to the last three rads in place of the 3/4" I used would balance the system?

The circulator is a Taco 007-F5. I've read that they are pretty good. The boiler was installed about 6 years ago.



Here's some photos:

http://i243.photobucket.com/albums/f...e/IMG_5490.jpg

http://i243.photobucket.com/albums/f...e/IMG_5492.jpg

http://i243.photobucket.com/albums/f...e/IMG_5493.jpg

http://i243.photobucket.com/albums/f...e/IMG_5494.jpg

http://i243.photobucket.com/albums/f...e/IMG_5495.jpg

http://i243.photobucket.com/albums/f...e/IMG_5496.jpg

http://i243.photobucket.com/albums/f...e/IMG_5501.jpg

http://i243.photobucket.com/albums/f...e/IMG_5503.jpg

http://i243.photobucket.com/albums/f...e/IMG_5504.jpg

http://i243.photobucket.com/albums/f...e/IMG_5505.jpg

http://i243.photobucket.com/albums/f...e/IMG_5506.jpg

 

It might support the air lock theory. You asked if putting bleeders on both ends would help. Maybe... if the end without the bleeder is at a higher elevation it might. Air of course will find the highest elevation and collect there.

Yes, I think you understand it correctly. But of course before you undertake such a project the wise thing to do is be absolutely sure that's the problem! You might be better off installing some balancing valves on the first few rads in the loop.

I think that would only make the situation worse, you would be adding more restriction to flow at the end of the loop than you already have. Unless you are talking about cutting and capping the 3/4 at the end before the last three, and running a 1/2" home run back to the supply off the boiler. If that is what you are thinking, I'd still use 3/4" and when you have that pipe open, I'd add balancing valves in those lines at that point.

A big part of you problem may just be that the 3/4" main is not big enough. I would think that with 10 rads on the loop, 1" would have been much more appropriate for the heat load.

In fact, the most appropriate solution might be to completely split the supply and return in half. Two 3/4" loops with seperate supply and return back to the boiler, each feeding 5 of the heat units.

I need to look at your pics again... are these 10 units the ONLY heat loads on the boiler ? And there is 3/4" pipe all the way from the boiler out and back ?

Yes, it's a fine pump. You may want to try swapping it out for a pump that will flow a bit more though, IF it can be determined that flow is actually the problem, and not air.

There are multiple options to consider, the most appropriate choice is the easiest, cheapest, one that WORKS!

By the way, the rads that you replaced with baseboard, were they metal cabinets with horizontal heating elements in them ? If so, those are called 'convectors', and chances are that they actually have a HIGHER BTU output than what you replaced them with. Can you elaborate ?

Lemmee study yer pics a bit more...

 

Pete, you might want to find a way to support that expansion tank. I don't like the way that thing is torqueing the pipe it's installed on. You could get a big ole hose clamp, and a piece of galvanized strapping. Run the strapping down from a rafter, and clamp it to the tank with the big ole hose clamp...

Can you describe the 'near boiler piping' ? I am seeing 1-1/4" off the supply and return, where does it go to 3/4" ? It's hard to judge pipe size from a picture, but it looks like that main run could possibly be 1" and not 3/4 " ...

I would also support that gas line where it runs over to the water heater off the main gas line to the boiler. You don't want that breaking !

 

The supply and return are actually 1 1/4" coming off the boiler then go through a reducing elbow to 1":

http://i243.photobucket.com/albums/f...e/IMG_5527.jpg

A 1/2" line comes off and goes up into the dining room rad.

http://i243.photobucket.com/albums/f...e/IMG_5531.jpg

http://i243.photobucket.com/albums/f...e/IMG_5535.jpg

A little further down another 1/2" line goes up into the kitchen and another into the living room rad. The main then goes behind a wall and from an access panel I can see a 1/2" line go up to the 2nd floor bathroom. That one is then reduced to 3/8". Then there is a reducing elbow on the main that brings them down to 3/4" which then feeds the remaining 6 rads.

I will support the expansion tank and gas line - thanks.

Some good news - I took your advice about easiest and cheapest options first. The possibility of an air lock seemed like a good place to start. You said that air will seek the highest point. Since I used pex tubing on a couple of the new rads, I had a little flexibility and was able to raise the bleeder side of the rad's core a couple of inches, bleed it, got some air out, and now rad #8 is hot! I tried the same thing with #10 and actually got some air and a little warm water out of the bleeder but it's still not hot.

What are balancing valves? I assume I install it on the supply side of a hot rad and turn it down, restricting the water flow to that rad thereby increasing it to the others, more or less?

If I was to add another pump would it be a big job? If I decided to do it would it be a big stretch to make it a two zone system?

The new baseboard rads are basic Slant Fins from Home Depot. Metal enclosures, copper tube with silver fins inside:

http://i243.photobucket.com/albums/f...e/IMG_5537.jpg

http://i243.photobucket.com/albums/f...e/IMG_5538.jpg

The old rads:

http://i243.photobucket.com/albums/f...e/IMG_5539.jpg

http://i243.photobucket.com/albums/f...e/IMG_5536.jpg

 

Now I understand much gooder! Thanks for the explanation, cuz I was scratchin' out what's left of my hair.

I'm glad you were able to get that air out and the water flowing. Woulda been a bummer to do a bunch of work and find out you still didn't have heat, eh ?

Balancing valves... there are real expensive ones that have flowmeters integrated, to inexpensive ones that are basically a ball valve without a handle, and a screwdriver slot to adjust, like this:
Balancing valve
These are what I have on my system at home.

Problem with using a ball type valve is that they are touchy to adjust. They aren't 'equal percentage' valves, meaning that if you close the valve 50% you get half the flow. No, you actually have to close a ball valve like 90% of the way to get half the flow. That's why they are so touchy, your adjustment range is limited to like 10% of the range of the valve.

Also, when they are that far closed, they can be a bit noisy. You may hear a whistly, rushing noise. Normally not a problem, but if it's in a quiet bedroom, it could get annoying at 3 AM ... If they're installed in the basement, not a problem.

You might consider trying 1 or 2 of these on the first two rads on the line, as an experiment, just to see if they actually do help get more flow to the end of the line. HD or Lowes won't have these, you would have to go to a plumbing/heating supply for them. You could try a standard ball valve too...

You could install it on the supply or the return.

When you say "add another pump" do you mean actually adding one ? or swapping the one you have out with one that might flow a bit more ?

Swapping the pump is pretty easy, fortunately the guy who installed the system did you the favor of including valves before and after the pump, so you don't even have to drain the system. You will get a 'little bit' wet just from the water in that short section of pipe, but not too bad...

Actually going to two zones would require a bit more work, but anything is possible, it just depends on how much you want to invest I guess.

Me, I'd try a different pump first, then maybe add a few balancing valves, and if that didn't work, I'd sell the place and move ... just kidding...

Now something you don't want to hear... you may not be happy with the heat output from those short sections of fin tube that you swapped. That one is what, 3' long ? If you've got average 170* water to that unit, you are probably going to get about 1500 BTU out of it. The old convector was easily double that, maybe a little more (assuming it was also 3'). If that's one that's at the end of the line, you could be even less happy...

If you have wall space available, you might think about lengthening that unit. You could do it by running one pipe under the baseboard unit and looping it back at the other end. Or look into a nice panel radiator ...

 

I'm with Trooper. I think you've dropped a package on your foot in replacing the convectors with baseboard. You are going to have problems with it. With the piping system you have, I doubt you will ever get enough flow thru the baseboard to get a lot of heat out of them. Bleeders on a horizontal run are little better than no bleeders. Sorry for all the negative comments but you have a mess there.

 

Sorry for the mix up with the old and new rads. The pictures of the new baseboard rad is in a very small bathroom, the older one is still being used in a bed room. I was just trying to show the difference.

As far as the new base boards pumping out enough heat - 3 out of 4 are working well - getting nice and hot. That last one never really got hot, even with the old rad, which is why I started this whole project in the first place! That old rad was 4 1/2' and I replaced it with a 14' baseboard. It's always been the coldest room in the house as it has three walls exposed to the outside and sits on top of an unheated garage. All that plus a cold rad and it can get a little chilly in there.

Adding a another pump? Sorry, my bad - I misunderstood. If I replace the one I have can you recommend one or tell me what I should look for? Are they expensive?

I could add three balancing valves in the basement for the first three rads pretty easily - except I'd have to drain the system again. Ugh.

I'm grateful for all comments I receive, even the negative ones. It's all part of doing it yourself, learning from your mistakes and then asking you guys how to fix it!

 

A bathroom is one place where you don't wanna skimp on the heat though. But if you find that you don't have enough heat, you can always change it out later for a higher output unit, and maybe even a heated towel rack!

14 feet of baseboard should give you about 7000+ BTU _IF_ and only IF the water going to it is hot enough and you can get enough flow through it.

I don't know if you saw my 'heat train' analogy in another thread or not... but basically if you think of the water as a train carrying heat, those heated passengers (BTUs) are getting off at the stations (baseboards). The train has to be going fast enough to carry the passengers to the station though, if not the station is deserted... not enough heat.

What's your boiler rated at ?

Some rules of thumb:

In general, system designers shoot for a 20* difference between the supply from and the return to the boiler.

With a 20* diff, you can expect to be able to extract 10000 BTU for each GPM of flow.

1" pipe is good for around 8 GPM, or 80000 BTU
3/4" is good for around 4 GPM, or 40000 BTU
1/2" is good for around 2 GPM, or 20000 BTU
(approximate values)

So you can see that by the time you get to the end of your heating loop, you need a minimum of 1 GPM to get rated BTUs out of that 14 feet of baseboard.

I'll look at some pumps later this evening and see if I can help with that. Some pumps are cheap (007 , 15-58) probably because they sell so many of them, others are pricey. Most of them will be a direct swap for the 007 you have. Even changing the pump alone might not get the flow you need though...

How difficult would it be for you to run 1/2" PEX out to that garage room in supply and return home runs from the boiler ?

 

I could run 1/2" pex to the boiler pretty easily . Do you think that's the best plan? Or would swapping the pump work?

If I run the pex from the cold rad, should I make it the first rad off the boiler? Or could I tap into one of the first three rads. The reason I ask is for some reason I feel more comfortable cutting into a 1/2" pipe rather than a 1" - my pipe cutter won't fit it, etc. - but I'll do whatever works better. Will running the extra 1/2" pex further tax an already overworked circulator or will the reduction in pipe size from 3/4" make up for the added length, about 18'?


I don't think there's a problem with heat loss, my very unscientific method of mesuring the heat in the pipes -you know the owww! method (touch it and if you say oww! then it's pretty hot) - tells me that the supply pipe is pretty hot right up to the rad, if I could only get it to go through it!

 

Is this a two story house above a basement, and are #8 and # 10 on the 2nd floor? And if so, are these the only ones on the 2nd floor?

And for what this is worth for all reading this: I maintain this rental that has scores and scores of in-series! 3/4 copper baseboard heat, on a one story house. An antique boiler fires it from one of those round cellars you have to crawl through a 'window' outside to get into that boiler 'room'. Believe it or not, the very end of the scores and scores of baseboard heat is as hot at the end as at the beginning! And it is all in series. This shows the power of what a good circulator pump can do, if it is circulating the water fast enough.

 

That's certainly the easiest, maybe the cheapest, and _might_ work... I would certainly try this before any major re-piping work. After all, the system has been _almost_ adequate all these years, it just might need a little more 'push' to do the trick.

I'm only bringing up the various 'options' for you to think about... pondering ...

I haven't looked at pumps yet...

 

It's a split level but yes #8 and #10 as well as rads #6 and #7 are on the top floor, 1 1/2 stories above the boiler which is in the basement . The basement is 1/2 level down from ground level. BTW, #8 is now hot so only #10 is still cold.

ecman51, I take it you believe my circulator is under powered?

 

I appreciate your pondering.

When looking at new pumps do I want an increase in flow range, head range or both?

 

Usually head capacity & flow rate both increase. You don't want a pump with a very steep pump curve. Most Grundfos circulators are 3 speed which is a really nice feature. It allows a lot more flexibility with one circ. Not sure if there is one on Grundfos's site or not but on Taco's web site there is a "wizzard" for helping in selecting the right pump for the job. I think on Bell & Gossett's site there is a chart or something for determining total head in the system. Knowing the head & desired flow rate make the pump selection a piece of cake. If you choose a 3 speed with the middle curve matching your needs or close to it, you are home free.

 

umm... I'm a little lost here. I've looked at all three websites and didn't get very far. It seems that the circulator that I have is very popular - Taco 007 - and I don't know quite what I'm looking for to replace it. The wizard on taco's website assumes that I know what I'm talking about. I found this Bell and Gossett NRF-33 but I'm not sure if it's a good replacement to boost output. Any suggestions?

 

Do you even know if that Taco is working?, or if you are just getting hot water, where you do, based on convection?

 

Pump selection is going to be a little more difficult because we don't really know the existing pump head on your SYSTEM. We know the 007 pump curve, but don't know it's OPERATING POINT because we don't know the system curve.

The 007 was re-designed last year and the new pump curve is much flatter, and it flows a bit more. Yours is 6 years old so it's of the old design.

The 007 can be had for $70 or so. The next logical Taco choice would be an 0010, and it's a big jump to $200 for that one.

The Grundfos UPS15-58 will flow more than the 007 at higher head, but the (new design) 007 will out pace it at lower head, even with the 15-58 on HIGH (it's a 3-speed). At medium speed, the 15-58 pump curve indicates it will flow a bit more than the 007 at higher heads.

The 15-58 is in the same price class as the 007 and would probably pump more in your system... but, it's a crap shoot.

I recently changed out my 25 year old 007 for a 15-58 and my delta T (difference between supply and return at the boiler) went from 30 to 25 with the 15-58 on high, indicating that it is flowing more. My system is pretty high head...

I didn't look at the B&G pumps yet...

ecman, there's a big ole flow check in his system, so I don't think it's gravity flow... but maybe the flow check is manually opened ?

 

Without knowing more about the system, it's hard to size a circulator properly but the Grundfos 26-99 will give you both more head capacity & more flow. If that's the circulator you choose to use, I'd start on low & increase the speed if you need to.

 

The low speed on the 26-99 is very close to the high speed on the 15-58, but I'm confused about something...

The Super-Brute series has three pumps, 15-58, 26-99, 43-44. The first two are interchangeable with the 007, the 43-44 is not, it's about 2" longer flange to flange...

but, in looking for pricing on the 26-99, I can't find the UPS 26-99, only the UP 26-99 which appears to be a single speed model. ?

What's going on ? Did G'fos discontinue the single speed 26-99 and replace it with the 3 speed and the distributors haven't yet updated their webpages ?

 

I checked one of my suppliers' sites & it lists the circ in one place as a UPS & another as UP. The description says 3 speed-1/6hp-115 volt. Not cheap.

 

The Grundfos 26-99 is around $200. Wow. I think I'll first try adding another bleeder to the cold rad. Should run me about $4. If that doesn't work I'll disconnect it from the main and run 1/2" pex back to the boiler. That should run me less than $50. If I still get no heat to that rad I'll spring for a new pump.
Thanks for all the help. I appreciate the time you guys have put in working on this. I'll keep you posted.

 

Yeah, I saw the price on that one too ... it's a huge jump from the garden variety pumps to the next size up.

Consider the 15-58 though... it's under $100 (I got mine brand new on ebay 'buy it now' for something like $60). I have proven to myself that it pumps more than the (25 year old) 007 on my relatively high head system. Whether that's because it was a really old pump or not ?... maybe .

Which would you rather try first, a bunch of piping changes ? or for around the same cost, swapping out a pump ?

I think if you re-piped that last rad, you would want to run BOTH the supply and the return back. With the return on the last one out at the end, you may cause even LESS flow through the others by upsetting the pressure differential across the rest of the far rads.

 

Well the price of the 15-58 is a lot easier on the wallet. I keep thinking that my house is really not that big, or high, and should I really need so much more power than I have now - if I went for the 26-99? So the 15 -58 might give me that little extra push I need to get to that last rad.
But if I do decide to re-pipe, I was going to run both supply and return. But I don't understand:

Could you dumb it down for me a bit?

 

I'm hoping the 15-58 will do it for you. The 26-99 starts where the 15-58 leaves off. It also draws more than twice the current as the 007 and the 58 ...

Dumbing it down boss!

Not really, but I'll try to explain it.

In order for water to flow, there has to be a pressure difference. When there is, water will flow from high pressure to low pressure. The amount of difference dictates how much water will flow. Basic physics... now:

In your mind (or on paper if you like!) sketch out your basic piping system. Your boiler, a pump on the supply, and a main line going out. Now at the bottom of the boiler is the return, also going out. Sketch those two supply and return pipes parallel, a couple inches apart. In between, add your heat terminals.

At the discharge of the pump, when the pump is running, is the highest pressure point. This pressure will steadily drop as it goes down the supply line, and more so at each terminal it passes, until at the end of the line, it will be pretty low.

At the return of the boiler (basically the suction side of your pump) the pressure will be the lowest, steadily increasing as it heads toward the farthest point on the return pipe.

Since we're pretty sure there is almost no flow in the last terminal on the line, it holds that the pressure on each end of that last terminal MUST be nearly the same. Hence, little flow.

If you were to disconnect the last terminals SUPPLY, and run it back to the highest pressure point, and cap the end of the main supply pipe there at the end, but leave the return piped as it already is, you know there will be good flow through that last one, right? yes, because of the large pressure difference.

But think about what happens on the return side if you do that. The pressure at that point that the last rad joins the return at the end is now going to INCREASE, perhaps even HIGHER than the SUPPLY side of the previous rads on the line. If that happens, you could possibly even REVERSE the flow in a few of them at the end. Basically, it would become a short circuit.

Did this make sense ?

 

Yes, I think I get it. Thanks for the detailed explanation. I'm actually starting to understand how my heating system works.
Now what will happen if I re-pipe both the supply and return back to the boiler. I assume there will be a nice pressure difference since it will then be the first rad off the supply side of the pump and the last one on the return. But will that affect the rad that was second to last and will now be the new last rad? I'm also concerned with the increased distance of pipe. Would that affect the pumps ability to get hot water to the the existing rads plus the longer distance to the re-piped rad?
I think your right that swapping out the pump is the easier way to go, and hopefully the 15-58 will have the power I need.

 

I probably exaggerated a bit when I said you might/could reverse the flow in the last rads. While it is theoretically possible, not likely. You COULD have very little flow through them as a result though.

If you moved both the supply and return back to the beginning of the runs, you would have PLENTY of flow through that last rad. In fact, maybe even too much. How far might the run be from the boiler out to that rad ? If you did this, I would suggest adding a valve so you could throttle it back if need be. In fact, since this will be the only heat terminal on the line, you might even consider installing a TRV (thermostatic radiator valve) in that room. If you did that, you could 'zone' that room by setting the TRV lower when not being used. When the TRV closes, you would get even more flow through the main loops. While you had the system drained to tap the connections in would be a good time to add balancing valves to those first few on the main line as well.

As for affecting the flow to the 2nd to last rad with a change such as this, you may find that it actually improves. A circulator pumps' 'operating point' is dictated by the amount of head (resistance to flow) that your system presents to the pump. If you reduce the resistance, the flow goes UP. By tapping that last rad back at the beginning, the pump will likely respond to this by actually increasing it's flow because it will see less resistance, and the majority of that extra flow will probably go into the re-piped rad (again, maybe _too_ much, so don't forget the valve).

When a pump is 'sized' for a system, it is always selected for the highest head loop, because if that's done, it will always be able to handle the lower head loops. Which is one of the reasons I suggested using 1/2" tubing if you re-pipe. You don't want that pipe so large that ALL the flow goes through there... (also the reason I recommend a balancing valve). This is also probably why you found some 3/8" tubing in your system...

But: definitely try a different circ first, because that may end up being all you need to do.

 

Well, I added another bleeder to the cold rad and ... no luck. Still cold.
I figure it's about 30' from the rad to the boiler.

So now I'm looking for a new pump. I saw a couple on e-bay. I'll let you know when I get it.

 

I think the guy I got mine (UPS 15-58) from on eBay was "Earth Movements" or something like that. I used a 'buy it now' for something like $58 if I recall... it's been a while. Fast ship, good deal.

Yeah, please let us know if the pump did the trick (I sure hope it does !).

 

If I may jump in, briefly.

If the system is full of water (i.e., not an airlock issue), then I agree that a larger circ may be in order, and/or some balancing valves or diverter tees at strategic locations. Your piping is kind of funky. 1/2" and 3/8" piping has a high head (head = resistance to flow). Hard to move lots of water through there. Lack of balancing valves or diverter tees probably doesn't help. Water being rather dumb (or smart?!), it always takes the path of least resistance. Given the choice between racing around a 3/4" loop and squeezing through a section of 1/2", it'll take the 3/4" unless you give it a reason (like a valve or diverter tee) to go the other way as well.

The 26-99 is a beefy beast. The Taco 0010 actually has not much more head capacity than the 007. It's a low-head, high-volume pump. These also tend to be big, noisy, and power-hungry.

I would try the 15-58. See what speed 2 does, and if that doesn't help, try speed 3. With the 15-58, you would take the flow-check out. However, if you still don't get improvement on speed 3, I would consider reinstalling the circulator's flow-check, and remove the big Taco flow-check from the supply piping. Replace it with a standard elbow. They have a fairly high flow resistance. Taking it out might get you better flow. Alternatively, if that flow check has an adjustment that can negate the check function, then just do that while using the internal 15-58 check.

Failing that, I would consider a diverter tee to the rad that remains stone cold. Diverter tees also have a fairly high head, but if you have adequate flow through the rest of the system, it may be able to handle it.

My $0.02.

 

Appreciate your $0.02. I'm currently bidding on a 15-58 from earth movement on e-bay.

I googled diverter tee and got a nice example of how it works:

http://books.google.com/books?id=WdP...nkhGxKG56ZtXsw

Are they only used in "one pipe flow through systems" or will it work on my one supply, one return pipe kind. Although since the cold rad is the last one on the line, that one rad is pretty much a flow through, right?

And I'll check if there's a way to adjust the taco flow check.

 

Xiph, the 3/8 that was in pete's system was a run off the main, feeding a rad, and I believe was intentionally used in place of a balancing valve in an effort to limit the flow to the rad to only what was needed.

I think a 3' wide 6" element convector is rated around 5000 BTU, so they only need .5 GPM to do their job, just about right for 3/8 tubing.

Pete, maybe you shoulda kept the 3/8 ?

A diverter tee _could_ be used to get more flow through a rad on a two pipe, but it would be at the expense of any downstream terminals. If you force more flow through one, less has to go to another. Your coldie is at the end of the run anyway. In your case, if the pump doesn't work, your next easiest choice for a fix is to throttle the early rads in the system.

How big are say the first two convectors on the line ?
i.e. width of element, end to end; and depth of element, front to back. And those are piped in 1/2", right ?

By the way... today at work I had an in depth discussion with one of our electrical engineers about your system, but he didn't know he was talking about water. He thought we were talking volts, amps, and ohms! I cleverly disguised my real intention. I asked him to help me with an Ohms Law problem. You see, VOLTS = PRESSURE, AMPS = FLOW, and OHMS = HEAD (friction). There's a direct relationship. So, I drew your system as a series of resistors representing the various pipes and rads. That one I could solve myself, but when I capped the supply and ran the last rad... errr, resistor, back to the supply it got REALLY complicated. I ended up realizing I'll never understand simultaneous equations, and we left it at that.

 

The screw thingy on top should be fully clockwise I believe, in order for it to operate as a flow check. If you go counter clockwise, it will lift the disc and allow gravity flow.

I think I'd pull the check from the pump and leave the Taco alone (clockwise).