Boiler leak

[Homey6660]

I have a slow leak coming out by the pressure release valve on my boiler. I'm trying to isolate whether it's the valve or the expansion tank (Amtrol -- or Extrol -- model #30). Could be other issues, I suppose (I'm obviously clueless), but I'm focusing on those two for now.

The leak happens when the system is operation. I turned off the thermostat and cut the water supply to the boiler and the leak stopped. There was water still in the pipes leading up to the release valve, of course, but it still didn't leak. When I turned the water and thermostat back on, there was a lag before it started leaking again...I'm estimating the lag was 1/2 hr to an hour.

Can anyone suggest to me specific steps I'd need to take to isolate the problem? I know I'll have to check the pressure. On that note, I do not have a pressure gauge near the expansion tank; the only pressure gauge is on the boiler itself. Maybe this is the pressure gauge I need to look at. Don't know. But, so far I haven't taken note of the pressure (I know I'll need to do that and will do so tonight).

Also of note -- I had had the whole system drained because I was working on fixing walls behind my radiators. The system was empty for approx 5 months.

Any assistance you can offer is much appreciated. Please do ask for clarifications if you need any.

Thanks, Mike

 

[Jadnashua]

The pressure should be the same anywhere within your boiler system, so looking at the boiler's gauge is fine. I'd put a bucket under the temperature/pressure relief valve's outlet. That may help you isolate where the leak is coming from. If I had to guess, and that is dangerous, I'd say you may have a blown bladder in your expansion tank or its pressure has leaked out. Quick first check is to wrap on the expansion tank and see if it is full of water (it shouldn't be) - plus look at the pressure gauge. Most systems operate at about one atmosphere - about 14-15 pounds. The relief valve is often a 20-25 pound setting. It doesn't take much to cause it to trip, and the thing that usually does it is the bladder tank. If you have a self-filling system, the valve may be letting too much water into the system as well.

 

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[Homey6660]

Here are some more details, though. I hope it can help prompt suggestions for next steps.

Two nights ago, I had turned off the water supply and the thermostat and had drained any residual water in the boiler (not in the whole system, though) by opening the pressure relief valve.

Last night, I checked the pressure and it was 11-12 psi under these conditions. I then turned on the water supply all the way. The pressure went up to 20psi very quickly. A dripping sound coming from the spout where the PR valve is (not actual dripping) could be heard maybe a minute after I turned on the water. Nine minutes after I turned on the water, i fussed with the valve leading to the expansion tank (I closed it and then opened it) and the drip sound stopped -- probably just a fluke, but I'm still noting it). Pressure was up to about 24psi twelve minutes after turning on the water. I kicked the thermostat on a couple of minutes later. It took 9 minutes for the pressure to top 30psi, getting to 32 when the leak started (which was 29 minutes after the water was turned on and 15 minutes after the heat kicked in). I didn't check the expansion tank before I started, but once the water was turned on, I tapped it with my fingernail. The lower 40% or so had a different sound from the upper part, which was more tinny sounding. But, it didn't "feel" like there was water in there and I certainly could hear any swishing when I rocked it a bit.

Honestly, I don't know if I have an auto-fill. What would it look like and where would it be? The source of water that I've cut is via a valve just upstream from the boiler. Just next to that valve, there's a red "reducing valve." That's all I've noted while not paying excessive attention to all the valves in that area.

Assistance is greatly appreciated.

Mike

The pressure should be the same anywhere within your boiler system, so looking at the boiler's gauge is fine. I'd put a bucket under the temperature/pressure relief valve's outlet. That may help you isolate where the leak is coming from. If I had to guess, and that is dangerous, I'd say you may have a blown bladder in your expansion tank or its pressure has leaked out. Quick first check is to wrap on the expansion tank and see if it is full of water (it shouldn't be) - plus look at the pressure gauge. Most systems operate at about one atmosphere - about 14-15 pounds. The relief valve is often a 20-25 pound setting. It doesn't take much to cause it to trip, and the thing that usually does it is the bladder tank. If you have a self-filling system, the valve may be letting too much water into the system as well.

 

[Bob NH]

All boilers like yours have a pressure reducing valve. Your is either set too high or it has failed in a way that allows a leak into the system.

Since it has worked until recently, and now is causing a problem, it is almost certainly failed. It may have failed because of the fact that it was empty for a while.

While you are getting around to fixing it, turn off the feed valve and release enough water to drop the pressure to about 12 psi. Your water system pressure could continue to cause the relief valve to release water. That could cause the relief valve to fail too.

There is usually a red mark on the pressure gauge of your boiler. Mine is at 20 psi. The pressure should be below that, always. The new valve, sometimes also called a regulator, should be set at about 12 psi. There is some kind of adjustment mechanism on the top of the valve.

It should not be too difficult to replace. You should be able to buy a new one at HD or similar. Try to get one that has the same connections and length. Mine has a union type connection on one end. It could be replaced with a couple of wrenches or channel locks and a wrench in about 10 minutes. Get thread tape if you don't have it.

Get the tools if you need them and do it. It will cost you about $150 to call a plumber and you will feel good about what you saved.

 

[Jadnashua]

Your boiler's owners manual should indicate the normal working pressure for your system. When you fill the system, that valve should stop the flow into the boiler's closed loop once it reaches that normal pressure if it is designed to do this automatically - it sounds like yours is. Once you turn the boiler on, the water expands. If there isn't someplace for it to go, since the water doesn't compress, the pressure will go up quite quickly until the pressure relief valve trips to bring it back down to a safe (not the preferred pressure) pressure. The expansion tank is where that water normally goes, keeping the overall pressure about the same.

Shut the boiler off. Drain enough water out to drop the pressure to zero. Get a tire pressure gauge and check the pressure on your expansion tank. It should be about 15 pounds. If you get any water out of that valve, replace the tank. If not, pump it up.

Open the valve to bring the pressure back to what your manual says then turn that valve off. Turn on the boiler and monitor the pressure. If the pressure rises much more than a pound or two, the bladder tank is suspect. If it doesn't, reopen the valve for the make-up water and watch the pressure gauge. One or the other of these two things is likely causing the system pressure to get higher than it should.

One last thing...a bunch of air in the system can cause problems, too. If your air separator is gummed up then the trapped air can expand, too and raise the pressure. The expansion tank might be overextended by the needed extra volume from this. As noted in the signature line, I'm not a pro, but I think I've got this down pretty well. You wouldn't hear water sloshing in the expansion tank, the bladder would either be holding it in place like a balloon, or if it has failed, it would be totally full of water. Basically, it should be nearly empty to maybe 1/4 full in normal operation as I understand it.

 

[Dubldare]

Not all boilers are equipped with an automatic fill/pressure reducing valve setup.

There are still some old fashioned gravity systems that are open to the atmosphere, utilizing a sheet metal tank installed at a point above the highest radiator.

Pressure is not the same throughout the heating system. 12# at the boiler gauge would be 3.32# at a point 20 feet above the boiler.

Pressure relief valves on low pressure, hot water boilers are set to open at 30#.

Water expands when heated. Pressure settings should be done when the system is cold to ensure that positive pressure exists at the highest points in the system. EG: 12# at 180° at the boiler may be 8# or less on a cool boiler, depending on size of expansion vessel. 8# at the boiler would be -0.68# at a point 20 feet above the boiler, a vacuum.

If you are using a bladder type tank, you may very well find that it has failed. A simple test would be to turn off the boiler, turn off the valve for the expansion tank, and simply remove the tank. If it has failed, there will be water in the tank, if it's ok, it'll be light. If it is light, also check the precharge pressure of the tank (the schrader valve). This setting should be approx 2# below your calculated cold boiler pressure.

To calculate your cold pressure: find out the total elevation, in feet, of your heating system, from the boiler gauge to the highest point of the system. Multiply the footage by .434, and add 3 or 4# for freeboard. EG: 20' * .434 = 8.68# + 4# = 12.68#. Extensive runs of small diameter piping may require slightly more pressure to be added in.

You will most likely also need to replace your pressure relief valve (as it may not be seating correctly; dripping before pressure is at 30#); and verify if your pressure reducing valve is leaking past, causing the excess pressure. When you stated that turning on your water feed resulted in the pressure jumping to 20# immediately, that leads me to believe that either your tank's precharge is set to 20#, or it is faulty.

 

[Homey6660]

Today I relieved pressure that was still at 26psi or so by letting some of the water out via the pressure relief valve. I got it down to 13 or so. I shut off the water supply that sits just ahead of the "reducing valve" (which you say is another term for auto fill valve). The reducing valve, by the way, is set for 12psi. When I kicked on the system, it did not go right up to 20psi like it had previously when I had the water supply on. BUT, after an hour or so (I checked for the first ten minutes, then left it and came back after an hour, so I don't know what happened in the intervening time), it climbed to 33psi and was leaking from the PRV. The expansion tank seemed just as empty as before. I checked the valve and it's open. (I can tell you that it's definitely turned all the way to the left...I'm assuming there's no way that would be CLOSED). Does this narrow it down to my expansion tank being the problem?

 

[Homey6660]

Jim, when you say air separator, are you talking about the bladder in the expansion tank? I don't hear any water sloshing around...wondering if that's the issue.

Your boiler's owners manual should indicate the normal working pressure for your system. When you fill the system, that valve should stop the flow into the boiler's closed loop once it reaches that normal pressure if it is designed to do this automatically - it sounds like yours is. Once you turn the boiler on, the water expands. If there isn't someplace for it to go, since the water doesn't compress, the pressure will go up quite quickly until the pressure relief valve trips to bring it back down to a safe (not the preferred pressure) pressure. The expansion tank is where that water normally goes, keeping the overall pressure about the same.

Shut the boiler off. Drain enough water out to drop the pressure to zero. Get a tire pressure gauge and check the pressure on your expansion tank. It should be about 15 pounds. If you get any water out of that valve, replace the tank. If not, pump it up.

Open the valve to bring the pressure back to what your manual says then turn that valve off. Turn on the boiler and monitor the pressure. If the pressure rises much more than a pound or two, the bladder tank is suspect. If it doesn't, reopen the valve for the make-up water and watch the pressure gauge. One or the other of these two things is likely causing the system pressure to get higher than it should.

One last thing...a bunch of air in the system can cause problems, too. If your air separator is gummed up then the trapped air can expand, too and raise the pressure. The expansion tank might be overextended by the needed extra volume from this. As noted in the signature line, I'm not a pro, but I think I've got this down pretty well. You wouldn't hear water sloshing in the expansion tank, the bladder would either be holding it in place like a balloon, or if it has failed, it would be totally full of water. Basically, it should be nearly empty to maybe 1/4 full in normal operation as I understand it.

 

[Jadnashua]

Two things...the system should have an air separator. This could be in one of several types. Basically, it is a means to automatically get air out of the system. One brand is Spirovent. They are sometimes called air scoops. There are other types.

It's not definitive, but it still sounds like the bladder tank is shot. If the pressure rose that much and the makeup water was shut off (unless that valve leaks), the pressure tank should have prevented the pressure from rising that much. Did you check the air pressure in the tank as suggested?

Borrow an tire pressure gauge if you don't have one. A definitive test is to shut off the system, let it cool enough so you won't scald yourself, relieve the pressure, then unscrew the bladder tank. If it is full of water, it is shot. Note, the tank is usually installed so it hangs down. If it is on its side, or up, then beware, it will dump potentially very hot water on you. Also, if it is full of water, it will weigh probably about 40 pounds or more (depends on the size). As noted, if working properly, it will only have a small amount of water in it when operating (and essentially all will get pushed out when the system pressure in the boiler is released if the bladder is not shot).

 

[Homey6660]

Just read your latest posts today, so I haven't tried what some of you have suggested. What I did do, though, was check the pressure in the expansion tank. There is none. However, there's no water either. That's one issue.

Related or not, the other issue is the pressure reducing valve (I have a Bell & Gossett). I read literature online that said the "cold water shut-off valve must be closed," as the constant addition of fresh water can cause corrosion and eventual failure of system components. I think the shut off valve had been left on.

 

[Jadnashua]

If your expansion tank's pressure is zero...it will fill up with water as you pressurize the system, and there will be no room for expansion. You must pump it up to about 14-15 pounds. If it won't hold air, you've found your problem, buy a new one and replace it.

If there aren't leaks, once your system is full, it should not accept any new water, so if the valve is left on (and it is working properly), you won't be introducing fresh water and therefore disolved oxygen into the system.

 

[Homey6660]

That's the thing, though. It has NOT filled up with water. Even though I might not hear a "sloshing" sound, there is no additional weight to the tank. So, there's no pressure...AND it's not getting water. We'll pump it up today and see if it holds air.

So, re: the water supply...I know you say it shouldn't take on any more water...but the PRV instructions do say that "the cold water shut-off valve must be closed," so I'll keep it closed.

If your expansion tank's pressure is zero...it will fill up with water as you pressurize the system, and there will be no room for expansion. You must pump it up to about 14-15 pounds. If it won't hold air, you've found your problem, buy a new one and replace it.

If there aren't leaks, once your system is full, it should not accept any new water, so if the valve is left on (and it is working properly), you won't be introducing fresh water and therefore disolved oxygen into the system.

 

[Jadnashua]

Is there a shut-off valve going to the expansion tank? Are you sure it is open? It won't slosh usually, regardless. If it doesn't have air, it can't do its job.

 

[Homey6660]

Problem solved...the valve going to the expansion tank was faulty.

Thank you all for your patience and help.