Bleeding slantfin hydronic


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Old 12-07-14, 10:05 PM
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Bleeding slantfin hydronic

When bleeding the slantfin hydronic radiator lines should the circulator be on or off?

I am thinking on so it pushes air bubbles toward the bleeder valve.

Thanks
 
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Old 12-08-14, 04:58 AM
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Originally Posted by zoneout
". . .I am thinking on so it pushes air bubbles toward the bleeder valve . . ."
I am thinking OFF (or while resting in between heating cycles) so that the bubbles can all rise naturally and accumulate at the highest point(s), hopefully where the bleeder is located ?

Otherwise, you get more water than air.
 

Last edited by Vermont; 12-08-14 at 05:29 AM.
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Old 12-08-14, 05:32 AM
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To bleed radiation of air increase the boiler water pressure to 25 psi. have flow only to the zone to be bleed , the pressure will make the air bubble smaller and the flow will move the bubble to the air vent.
 
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Old 12-08-14, 09:13 AM
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You'll get as many opinions one way as you will the other.

Fact is that the only 'correct' way is the way that works.

There's valid reasons for bleeding cold, hot, pump running, not running...

Maybe the questions from us to you should be

" What is the problem? " " Why do you want to bleed your system? "
 
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Old 12-08-14, 09:42 AM
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The problem is there are 3 floors each a separate zone with its own circulator. 1960s original slantfin baseboard with American standard boiler. Anyway yesterday I noticed the top floor circulator was running constantly. So I touched the return pipe and it was cool. All I can figure is that there is a lot of air in the line blocking the flow.
 
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Old 12-08-14, 11:02 AM
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there are 3 floors
At this point we need to ask about the boiler PRESSURE, because if you don't deal with WHY there is air in the system, the problem will only return.

If you try to bleed the 3rd floor rads and nothing comes out, or air acutally gets sucked INTO the bleeder, it means there isn't enough pressure in the system.

Go to the boiler and tell us the readings on the PRESSURE / TEMPERATURE gauge.
 
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Old 12-08-14, 11:21 AM
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Pressure 15 psi and temp fluctuating between 130 to 170.
Btw, the lower 2 floors seem fine.... Return pipes quite warm to the touch.
 
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Old 12-08-14, 12:31 PM
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First off, chances of a boiler gauge being accurate are slim. Those old square gauges were pretty good though. But read this:

http://www.doityourself.com/forum/bo...ure-gauge.html

Presuming that the gauge is in fact accurate, your pressure is probably too low.

Lets say your three story home has the highest piping 30' above the boiler.

The MINIMUM pressure when the boiler is cold would need to be SEVENTEEN PSI... and that's COLD. Pressure will be higher when the boiler is heated.

Any less pressure in the system will mean that the upper radiators are below atmospheric pressure and air bubbles will form and the flow will be stopped.

So, before you try to bleed, you need to determine that your pressure gauge is accurate, and find the reason that the pressure in the system is low, and then raise the pressure up to where it needs to be.

and THEN bleed the air out.

I'm guessing that you have the old style expansion tank in the joists above the boiler, correct?

I'm pretty sure once you raise the pressure to get the hot water back to the upstairs you are going to be telling us that now the pressure relief valve is leaking.

Then we're going to have to instruct you how to drain that expansion tank properly...

That's the thing with these old systems... one thing happens and it snowballs into a whole string of things because they are all dependent on each other.
 
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Old 12-08-14, 04:43 PM
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Thanks. Ok - will be putting together a verification gauge tomorrow.

I would estimate the top floor baseboards to be about 20 feet max above the boiler (I counted the basement as 1 story)

Water pressure comes from NYC supply and thru the automatic feeder valve.

Your guess on the old-school expansion tank in the joists is correct!
 
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Old 12-08-14, 04:51 PM
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I would estimate the top floor baseboards to be about 20 feet max above the boiler (I counted the basement as 1 story)
OHHHH... OK... so it's a TWO story home with boiler in basement then?

If that's the case, then 12-15 PSI when the boiler is cold is fine.

If you're seeing 15 PSI when the boiler is at 170F it's still probably a bit low in pressure because when the boiler cools it likely goes below 10 PSI (or less!)

Can you take and post some pics of your system so we can look to see what valves you have available that will facilitate purging the air from the zones?

I do also advise a drain of your expansion tank.

More questions:

Do you produce domestic hot water with your boiler? or is there a separate stand alone water heater?

Do you know if your boiler is a 'warm start' where the boiler maintains a warm temperature at all times regardless of a heat call from the thermostat? Or is it a 'cold start' that would cool completely if there were no heat call?
 
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Old 12-08-14, 05:33 PM
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Right... 2-story home with boiler in basement. Sorry, my bad.

The only valves I know of are the typical screw-type manual bleeders on the baseboards. There are about 3 of them in that top floor zone in different rooms. I didn`t notice any type of bleed valve around the boiler itself.

I did the knuckle-tap test on the expansion tank and it sounded mostly hollow (about 3/4 empty is my guesstimate).

Separate stand-alone water heater. (Though at some time in the distant past there may have been a tankless coil used from the boiler - just a hunch)

Boiler is warm-start with a Honeywell aquastat low limit set at 150 deg and 15 deg differential.
 
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Old 12-09-14, 08:09 AM
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I didn`t notice any type of bleed valve around the boiler itself.
Not necessarily 'bleed' valves that we're looking for, but 'purge' valves... need pictures of system and piping/valves all around.

I did the knuckle-tap test on the expansion tank and it sounded mostly hollow
Useless 'superstition' that one can determine water content in a tank by tapping.

may have been a tankless coil used from the boiler - just a hunch
If so, you would see an abandoned pair of pipes exiting the boiler... are there?

Boiler is warm-start with a Honeywell aquastat low limit set at 150 deg and 15 deg differential
Not going to divert the discussion at this point as to possible reasons that you may be wasting fuel with this strategy... because it might be necessary, depending on other factors... but for the time being, at least turn the LOW down to 140F.

What is the HIGH setting?
 
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Old 12-23-14, 03:22 PM
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OK, sorry for the delay. Got some photos.

Couldn`t see any abandoned pipes from the boiler so looks that HW was always separate tank.

Aquastat high is at 180. There are separate circulator relays through so I dont think the Aquastat high comes into play.

Here are the photos....
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Old 12-23-14, 03:27 PM
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More pix...................
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Old 12-23-14, 03:40 PM
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There are separate circulator relays through so I dont think the Aquastat high comes into play.
Yes, it does. The aquastat will cut the burners off when the water temp reaches the setpoint.

Your gauge is showing just a hair over 12 PSI with the boiler at 180F. This is too low even for a 2 story home because it means when the boiler cools the pressure is going to be way below that.

will be putting together a verification gauge tomorrow.
Did you?

Show me the expansion tank and the piping to it.

Show me the water feed valves.
 
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Old 12-29-14, 07:21 PM
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OK, 55 year old American made boiler gauge still accurate. Verification gauge below shows the same reading of about 12.5 pounds.

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Old 12-29-14, 07:24 PM
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Here is the expansion tank with water feed valve to the left...

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There is a shutoff valve on the line feeding into the expansion tank just out of view on the photo.
 
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Old 12-30-14, 07:46 AM
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I'm not sure the piping...

I see a water line coming up, a ball valve, then into the pressure reducing valve, out of that valve and doubling back toward the wall where there is another ball valve, then that connects to that vertical pipe?

Is that correct?

Now the expansion tank piping... I see the pipe coming down and toward the wall from the tank, but then it either tees into that other vertical pipe, or it elbows down to someplace... and you say there is a valve below, out of the picture.

Is it the camera angle that makes it look like it's teeing into that vertical pipe? And that vertical pipe is 'hiding' behind the pipe from the tank?
 
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Old 12-30-14, 08:50 AM
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Right - the black vertical pipe from the ceiling is the cold water supply - the tee in the middle feeds the boiler and the elbow at the bottom goes to the HW tank.

Right - the camera angle makes it look like the expansion tank pipe tees into that pipe in the back. Thats actually the return pipe (foam wrapped) from the HW tank going up into the ceiling.

The pipe from the expansion tank just goes down into the boiler and there is a shutoff valve just out of view.
 
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Old 12-30-14, 09:13 AM
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Here`s another view that shows the expansion tank pipe more clearly...

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Old 12-30-14, 09:20 AM
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OK then...

The first thing you should do is drain that tank.

The only 'tricky' part about that is once you start draining, a 'vacuum' will build in the tank and the drain flow will stop. You'll think it's empty, but it's not.

Using the shortest and largest diameter hose possible, with no coils, loops, etc will help.

Close the valve leading to the tank to isolate from the system (of course, shut the boiler down while doing this) and connect hose to drain.

Open drain to start emptying...

when flow stops, you need to break the vacuum.

Sometimes just leaving the hose on the drain a bit loose will be enough to allow it to suck air, or taking it off and putting bucket under and opening drain will allow it to take a 'gulp' of air.

In the olden days guys with better lungs and immune systems than I have would blow into the end of the hose... do that at your own risk... and understand that you could end up with a mouth or face full of nasty old boiler water...

Do you have a small air compressor? If so:



Even if you don't have the compressor, using a wye fitting will make it easier than putting the hose on and taking it off.

After you got the tank empty, and you're sure it's empty, close the drain and open the valve to the tank.

Water will feed and the tank will refill 1/2 to 2/3 with water and you will have an air cushion at the top of the tank.

With boiler now cold, check pressure... it should be right around 15 PSI.

With that out of the way, we can purge the upstairs zone... next...
 
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Old 12-30-14, 09:22 AM
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Ya know what? I just looked at the first tank pic again and it looks like there might be a 'vent' fitting on that drain.

Is that a screw on the side of the fitting above the tank drain valve?

That might make it easier to get air into the tank if it is what I think it is.

Can you get a closer shot of that please?
 
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Old 12-30-14, 10:11 PM
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Yep, that was a vent fitting. When I backed out the screw, water started gushing out. Sure beat blowing into the hose. Thanks, all went smoothly. Pressure right back up to 15 psi.

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Old 12-31-14, 06:58 AM
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I'm amazed at those old square gauges... they were quality built! Ahhh, the good old days!

Pressure right back up to 15 psi.
Are you saying that the pressure dropped in the boiler when you were draining the tank?

It should not have, since you had the valve between tank and boiler closed... it might have dropped when you reopened that valve, but would have recovered quickly.

When the boiler fires now, how high does the pressure go when it's HOT?

Still no heat upstairs?
 
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Old 12-31-14, 11:43 AM
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Are you saying that the pressure dropped in the boiler when you were draining the tank?

It should not have, since you had the valve between tank and boiler closed... it might have dropped when you reopened that valve, but would have recovered quickly.
No, it didn`t drop while draining the tank... it dropped well below 10 psi when the expansion tank feeder valve was opened. 10 psi being the low limit on the pressure reducing valve so I could hear it feeding more cold water till it got to 15 psi then stopped. Now I understand why it didn`t bring the pressure up when it was at 12 psi.... it hadn`t breached the low limit at that point.

Will go back to get the pressure when hot shortly..... thanks.
 
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Old 12-31-14, 01:43 PM
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Will go back to get the pressure when hot shortly
OK, I just want to make sure that when you bleed the upstairs and raise the pressure if necessary that you won't have the relief valve opening and spewing.


Still no heat upstairs?
Yes? No?
 
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Old 01-01-15, 03:51 PM
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OK, so checked today and my system is defying the laws of physics. With the boiler hot the pressure went down to 14 psi.

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Old 01-01-15, 04:00 PM
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I happened to notice a real slow drip from the expansion tank feed shutoff valve. About a drop every 3 minutes. Could that cause this problem?

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Old 01-01-15, 04:03 PM
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I was able to snug that bonnet nut about an 1/8th turn and the dripping stopped. What now?
 
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Old 01-01-15, 06:19 PM
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With the boiler hot the pressure went down to 14 psi.
The other gauge agrees?

About a drop every 3 minutes. Could that cause this problem?
Doesn't seem like enough to make much difference.

You still haven't answered...

STILL NO HEAT UPSTAIRS?
 
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Old 01-01-15, 07:06 PM
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What now?
I would wait until spring and replace the valve - it doesn't look good.

If it starts leaking again, and tightening the packing nut doesn't help, try opening the valve all the way onto its backseat, assuming it has one.
 
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Old 01-01-15, 08:33 PM
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If it starts leaking again, and tightening the packing nut doesn't help, try opening the valve all the way onto its backseat, assuming it has one.
Thanks for the suggestion. I usually try to avoid that since I`ve noticed that`s usually when the stem seizes up. But in this case it might buy me time until I can replace the darn thing.
 
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Old 01-01-15, 08:38 PM
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With the boiler hot the pressure went down to 14 psi.
The other gauge agrees?
Yep

You still haven't answered...

STILL NO HEAT UPSTAIRS?
Right. The return pipe from upstairs is cold.
 
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Old 01-02-15, 06:30 AM
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might buy me time until I can replace the darn thing.
If you stopped the leak by snugging the packing gland nut, there's no urgent need to replace the valve. You can of course if you want to, but it's not necessary if it's not leaking.

What's the clothes pin for?

The return pipe from upstairs is cold.
Let's purge that zone then.



Turn boiler OFF and allow to cool to 100F or less... you do NOT want to feed a lot of cold water into a HOT boiler! This is important!

CLOSE all three of the yellow handle ball valves.

Connect hose to drain above the ball valve on the zone that's not heating.

Submerge end of hose into a bucket so you can see when bubbles stop.



That lever on top of the pressure reducing valve is your 'fast fill' lever. Lifting that will bypass the regulator portion of the valve and allow a faster flow to push the air out.

Open the hose drain.

Lift the lever on the reducing valve and keep an eye on the pressure gauge. You can 'modulate' that lever and keep the pressure below 30 PSI in the boiler. Keep feeding water at a fast rate until no more bubbles.

Release fast fill lever, close drain.

Open yellow ball valves.

Return to service... should be OK now.

Make sure pressure in boiler when cold is at LEAST 12-15 PSI.
 
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Old 01-02-15, 10:47 AM
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What's the clothes pin for?
That`s my handy-dandy reminder for which pipe feeds the first floor. Might get some real labels in my next lifetime.
 
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Old 01-05-15, 12:08 AM
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OK, got enough air out of the top floor zone to fill a blimp. Back in service and the return pipe is hot now. Pressure 16 psi cold and 18 hot. I think that slow valve leak allowed the pressure to drop before. Seems steady now but I`ll keep an eye on it.

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