Weil Mclain Gold boiler and a Weil Mclain Gold indirect fired hot wanter tank; both installed in 10/2003. Both have been working just fine aside from the random issue here and there (leaky backflow, leaky pressure releif). It's a baseboard hot water heating system with two zones for heating one extra zone for the hot water tank. One circ pump, 3 zone valves.

Last week, our pressure gauge was filled with water and leaking. The tech came out and replaced it. (Not covered under the svc contract )

The next morning, I noticed the backflow valve and pressure valve were leaking. The tech came out and we shut off the supply line to see where the pressure was coming from. He was concerned that it "may" be the hot water tank. He said that if we shut off the supply, and the pressure stayed the same, we could rule out the tank. Pressure was set for 15 psi...and stayed there. It may have dropped to about 14, but it did not rise.

They thought it may be the supply valve. Another tech came Friday. The expansion tank wasn't holding pressure. The bladder was good, but the valve used to fill it with air was leaking...replaced that. We also turned down the aquastat. That was set to 210! He went banannas when he saw that. We turned it down to 160.

Now the boiler sits at 20psi. The tank was checked with a gauge when the system depressurized...it was at about 13psi I believe...so it's not the expansion tank.

When the boiler fires and the circ pump is on, the pressure drops to around 15psi. When the boiler is not on, the pressure is about 20psi.

The guy said it really shouldn't a problem...as long as it's not getting up to 30psi and popping the releif valve. It's worked fine all weekend...and holding at 20 psi.

Is 20 psi OK? I'm a little more OCD than your average homeowner...I just want to be sure.

Thanks in advance.

 

This just can't be right... how can the pressure DROP when the boiler is firing?

When the boiler is COLD, the pressure should sit around 12-15 and go UP when it fires and the water is heated.

 

I know it sounds crazy, but that's what's happening. Right now, the boiler is off....it's at 19-20 psi. When it fires, the pressure will drop to about 15psi.

 

Glenn, can you take some pics of the system and post them for us to view? Maybe we'll have one of those AHA! moments when we see them...

Free account / Image hosting, free photo sharing & video sharing at Photobucket / upload pics there / place link to your album here.

 

The answer to your question though... is 20 PSI OK ? would normally be YES, when the boiler is HOT. But this weirdness with the pressure makes me want to have a look see...

 

No problem! Sorry for the pics, I just took them on my Blackberry.

Boiler1.jpg is of the setup, Boiler2.jpg is the pressure with the boiler off, Boiler3.jpg is the boiler running after I turned up a t-stat to call for heat.

Boiler Pressure pictures by glennmj99 - Photobucket

 

I didn't really need the pics of the gauge, I believe ya! I wanted to see the piping all around the boiler, the valves, pumps, all that stuff... but I don't think the blackberry pics are gonna cut it... can't really see any detail.

 

I do actually have a theory though, from what I see so far... where is the expansion tank connected to the system?

 

I see 146 deg at 20 psi.

and 153 deg at 18 psi

We need to see the gauge when the whole system is at room temp - less than 100 deg.

Is this a warm-start boiler - i.e., the boiler stays warm constantly? Like Trooper, I also may have a theory, probably different from his.

 

Yeah... Glenn, turn the boiler off and let it cool all the way down... tell us what the gauge reads then.

 

I'm with Trooper's unstated theory. That circ's inlet is right on the heat exchanger. And I'll bet the exp tank is just out of the photo to the upper right. The 5 psi drop is being caused by negative pressure in the boiler when the circ turns on.

In a geeky way, it's kinda cool. Does it affect performance? Perhaps not.

Glenn, do you have any air problems with this system? Gurgling pipes and such?

Is the little cap on the air vent open or closed?

 

Sorry for the delay guys!

It's a warm start unit. We have an indirect fired tank, so the boiler is always on; year round. (and that tank is way way way better than the old domestic coil we used to have!)

No gurgling issues. The system runs normally to me. Well, aside from this odd pressure issue. The pressure tank was just replaced on Friday...it's at 12-13 psi. It's above the boiler itself. The tech bled all the air out of the system when he refilled it after bleeding off the pressure to install the new tank.

I uploaded some more pics. I figured out why they came out so cruddy...there was a big fingerprint on the camer lense on my BlackBerry. D'oh! It should give you the lay of the land regarding the plumbling and whatnot. I can take more pics or point out where specifics are if needed.

Here's another odd situation. On Friday, when the tech was there, when the circ pump ran, the pressure dropped. When the boiler fired and the pump ran, the pressure dropped. Now, when the circ pump runs, no pressure drop. The pressure only drops when the circ pump and the boiler are operating.

Link to pics: Boiler Pressure pictures by glennmj99 - Photobucket

 

The expansion tank is plumbed in the worst possible location relative to the circulation pump BUT if the only problem you have is that the pressure in the boiler drops slightly when the pump runs then there is no need to change anything.

If you have an indirect water heater there is no need to keep the boiler hot year-round. You can lower the "low limit" of your aquastat to the lowest point or you can change the aquastat to a model that does not have a low limit.

 

Not that I plan on changing anything... Where should the pressure tank be mounted?

The aquastat is set to 160 right now. So if it were to be set lower, would the external tank call for water instead of the aquastat?

 

Glenn, have you been able to let the boiler cool and get a pressure reading yet?

If your boiler is in fact a 'warm start', there should be THREE dials inside your aquastat box, a HIGH, LOW, and DIFF.

Take a look and tell us what they are set to.

Google the term "pumping away" and ignoring any possible hits on porn sites, read some of the info pages that you find. This idea of pumping away is somewhat 'new'... at least in acceptance and application, and MOST of the old school installers will have no idea WTH you are talking about if you mention it to them. "That's the way we do it, because that's the way we've always done it." is probably the response you will get. I don't think this is an industry that is big on 'continuing education'!

 

I haven't. Maybe I'll give that a shot this evening. I'll try and get it to 100 or under.

I'm about 95% sure there's only one dial in the box. I beleive that's the low limit dial? I can take a pic of that and post it up.

 

Turn off the burner and run the circulator - that will cool things down quickly.

 

Probably the HIGH limit. If you only have one dial, your boiler should be a cold start.

When you confirm that you do have only one dial, we can talk about that setting a bit... or if you have three, we'll talk about that too!

 

How's he gonna do that Mike? without ripping into the wiring that is...

 

I've been ass-suming this is a gas-fired boiler. With a warm-start gas-fired boiler: turn the gas valve to PILOT and turn up the thermostat. The burner is disabled and the circulator should start.

But now that I see an indirect water heater, maybe it's an oil-fired boiler? (Natural-gas users do not use indirect water heaters as much.)

 

I'm purty sure I see a swing door with an earl burner onnit.

If I had gas... I mean if I had natural gas piped in from the street... I would probably still go for an indirect, but can certainly understand why someone with gas available would choose the cheaper (short term cheaper) route and go with a gas fired WH.

 

Trooper: Here in natural-gas country, you can go to the big-box stores and find many gas water heaters to choose from - perfect situation for DIYers. Plumbers usually carry a 40-gal gas heater on their trucks.

Ask for an indirect here in the Midwest - they'll say, "What?" I'm sure you can get one, ordered special, but you might need to get your pocketbook out. Standard 40-gal, natural-gas water heaters cost, here, less than $300. And, you don't need to fire your big old boiler all summer. Better not move to the Midwest - to big a shock for you, particularly the low energy prices!

 

Another detail I left out! It's an oil fired unit.

I opened up the box last night...there's only one dial in there. It's set to 160. So based on the posts, that's the low limit. Before, it was set to 210! Yikes!

I'm not sure how to get the circ to run without the boiler kicking on. I can open up the box, manual turn on the circ, but the burner will fire up shortly after. And on another note....I was incorrect about the circulator. When I turn that on manually, the pressure does drop.

We're still holding steady at 20psi...and no leaks.

 

No... That single dial is your HIGH LIMIT. In the presence of a continued heat call from either the space heating OR the indirect, the burner will heat the boiler water to 160 and shut off... until the boiler water cools to around 145-150 or so, and if the heat call continues, the burner will re-fire. As long as there is a heat call, the circulator will run. If the burner cuts off on high limit, the circulator will continue to run.

What's more, in the ABSENCE of a heat call, your boiler should go stone cold. If neither your thermostats or your indirect call for heat the boiler should NOT run.

Let's talk about that temperature setting dial that is now at 160...

First, since you have an indirect water heater, there may be times when you WANT hotter water in the boiler to speed up recovery time on the water heater... i.e. back to back showers, laundry day, etc... as far as space heating goes, you probably will not notice a lack of heat in the home during the mild fall and spring 'shoulder' seasons, but it might be possible that when it gets really cold out that the 160 water will not heat your home to your liking. The 'normal' setting for that dial is 180... that is the 'design temperature' of almost all hydronic heating systems. If you find that you start to run out of hot water on occasion, or that when it gets real cold out you wish for a little more heat in the home, then push it back up to 180.

And ?

There is a reason we have asked this... just turn the switch off and wait a few hours... don't worry about getting the circ to run... just be patient... it will cool off.

We can't give you a definite answer if the 20 is OK when hot until you tell us what the pressure is cold... so just DO IT!

 

Great info! I'll certainly keep an eye on things with regards to off season hot water. It's easy enough to adjust that dial if needed.

HA! I'll do my best! It's gong to be tough this holiday weekend to shut of the boiler with company food prep and all that fun stuff. So if I don't get to it this weekend, I will next week.

 

I believe there is still some uncertainty here about your aquastat. Can you give us the make and model number? There may be a sticker on the inside of the front cover. Also, a close-up photo of the aquastat with the cover off would help, too.

Some Honeywell high-limit aquastats have a small, second thumbwheel partially hidden behind the snap-action switch - if so, that is the differential.

 

Sure! I can post a pic of that in a bit for you.

 

It's a Honeywell L8148A.

I uploaded a pic to the album: Boiler Pressure pictures by glennmj99 - Photobucket

 

See below, High limit only control.

Aquastat Controllers
200 customer.honeywell.com 70-6910
L8148 Aquastat® Relay
Immersion-type controllers that combine high limit protection with
switching relay control of burner and circulator motors.
• High limit opens burner circuit only.
• Include transformer and accessory terminals for adding a remote low
limit controller.
• Case available for horizontal or vertical mounting.
• Requires a 24 Vac thermostat with heat anticipator set at 0.2A.
Setpoint Temperature Range: 240 F (116 C)
Operating Range, High Limit: 120 F to 240 F (54 C to 116 C)
Maximum Operating Pressure: Immersion Well: 255 psi (Immersion
Well: 1757 kPa)
* L8148A1017 High Limit 8 F fixed
* L8148E1265 High Limit 15 F fixed

 

I'm convinced. You're correct.

 

I never had any doubt, and am glad we're all on the same page now!

Earlier, Xiphias 'channeled' my thoughts accurately. What is happening here is that the way your circulator and expansion tank are mounted, when the pump runs, the suction of the pump is SUBTRACTING from the pressure in the boiler. While this certainly is not an IDEAL situation, as long as it's the ONLY symptom, then there is NO PROBLEM.

If you don't have continual problem with air gurgling through the system, no problem.

If you don't have problem with the drop in pressure causing the pressure reducing valve (which is feeding into the boiler at the return inlet to the boiler) taking in 'sips' of water when the pump activates and slowly raising the pressure in the system, no problem.

The latter is the reason I want to see what the boiler pressure drops to when the system goes cold. If it drops to 12-15 PSI cold, it means you are good to go.

DO keep an eye on it in the future though, because it is POSSIBLE that over time you may get a slow increase in pressure.

 

Thanks! That makes sense. The boiler has stayed at 20 all weekend...luckily,no increase...and no more leaks! I'll certainly keep an eye on things.

I'm glad to hear that this is "OK" given how the system is plumbed. Again, I'll keep a close eye on it. I appreciate all the help; and I'm glad it's not a big deal i the end.

 

I'm back!

The pressure had increased over a number of weeks, so I called our oil company. I had someone come in around December 28 or 30th and they replaced the feeder valve. The pressure was a bit north of 15 when he was done and dropped to about 15 when the circ came on. Great!

I checked last night and when the circ is off, the pressure is up to around 30 psi. I'm stumped guys. We had ruled out the indirect tank, but now I'm confused. Another confusing thing...the gauge said 30 psi...but the relief valve was not dumping. And that valve is less than a year old.

 

I didn't read back in the thread so I don't know if this was covered or not. Was the accuracy of your gauge verified? Was your expansion tank determined to be in working order?

 

New gauge was installed in late November, the old one was leaking. New expansion tank was installed shortly after. I was with the guy (kinda helped, he needed some teflon tape and I used my pressure gauge to measure the pressure) and the tank is up to snuff; brand new.

 

Glenn, the location of the water feed valve could be the culprit... earlier I said:

With the valve set to say 12 PSI, when the pump kicks in and the pressure in the boiler drops BELOW that setting, the valve could be slowly feeding water into the system.

What I would do to diagnose is this:

Shut off boiler and let cool to under 100°

Let water out of the system to drop the pressure to 12 PSI.

CLOSE THE MANUAL SHUT OFF VALVE ahead of the pressure reducing valve and run the boiler that way for long enough (days, weeks) to determine if the pressure will now remain stable. There is NO PROBLEM running with the manual valve closed, AS LONG AS you keep an eye on the pressure gauge.

If it DOES remain stable, you know that the valve is feeding water when it shouldn't.

Reason for that? either the above mentioned pressure drop when the pump kicks on, OR the new valve is either defective, or got some 'crud' from the pipes in it when it was installed. This can and does happen if the installer does not thoroughly flush the water line before installing the new valve.

 

Is the manual shut off valve basically the domestic water supply? I want to make sure I'm n the same page!

The boiler is sitting at about 29/30psi when warm. When the circ kicks on, it drops to about 23-25psi. It's hard to read exactly.

What's the easiest way to bleed some pressure out of the system? I know there are a few drain spiggots on the unit. IIRC, that's what the techs use when they come here.

 

No, not the shutoff for the whole house. There should be a valve ahead of the pressure reducing valve (auto fill valve) - the valve, if I understood you correctly, was just replaced. Please post some more photos of the valve that was replaced and everything piped ahead of it and behind it.

 

Glenn, I believe the valve I'm talking about is visible in this picture. It's the 1/4 turn ball valve in front of the expansion tank... the water supply comes down from the ceiling, a 1/2" pipe, then the ball valve, then the Watts 9D backflow preventer, then it turns and goes down to your pressure reducing valve, then into the boiler...

 

Oh... yes, any boiler drain will serve to drop the pressure in the system. Choose the one that is most likely to close again after you open it!