# Pressure Relief Valve Keeps Blowing



## puzzled (Dec 15, 2007)

Hi guys! I was hoping somebody could help me out here. My husband and I have been going absolutely crazy the past couple of weeks thanks to some issues with our boiler. 

A little background info...We have an old Peerless gas boiler which I believe is original to the house (making it roughly 30 years old). Two weeks ago I heard what sounded like an explosion coming from the basement, (it was LOUD!) followed by all sorts of roaring, clanging, and what I thought to be smoke filling the basement which actually turned out to be steam. I called the fire department because I thought we had a gas explosion. Turns out the pressure relief valve on the boiler blew. Ooops.  In my defense it blew things straight across the basement and completely melted the circulator so it did cause quite a ruckus. 

Anyway, we've since had three different repairmen here to try to solve the problem to no avail. We've had pretty much every part replaced, some of them more than once in the past couple of weeks-zone valves, pressure relief valve, expansion tank, aquastat, water feed valve, circulator, etc. The damn relief valve still blows randomly. I'll hear a loud rush of steam that may last for up to 40 seconds, followed by silence, followed by another loud rush of steam. This may last for up to 3 minutes. I checked tha gage after one of these episodes and the pressure was reading near 90! and the water temp was about 280 degrees! The weird thing is this occurs so randomly. It was working ok for maybe 4 or 5 days and then decided to blow one night and has continued to do so at random-sometimes a couple of times a day, sometimes once a day. 


Well, apparently the damn relief valve had enough because this morning I woke up to what sounded like water running. I went into the basement and was greeted by water gushing and 2 inches of water in my basement. My husband turned off the water and the repairman came to check it out. The thing puzzling everyone is what the heck is causing the psi and water temp to rise so drastically from time to time? He actually installed a second expansion tank which he said is unheard of for a dinkly little boiler like ours, but it seems to be keeping down the pressure (it's hanging out at 11 psi as opposed to being in the 20's.)  Anyone with any hypotheses? This is very frustrating and I'm afraid to leave my house for fear of another flood! Thanks in advance for any advice you may have.


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## webbie (Dec 15, 2007)

No doubt you have control problems, not PR problems. Bad news. I'll let some boiler experts chime in, but if we assume (from afar) that they replaced the control properly, and that it worked before, then I suspect the well that the aquastat is inserted into - like it may have some buildup on the water side (the part exposed to the boiler water) of the unit, and the temperature of the water is not reaching the aquastat......

BUT, the random thing is confusing....rules out my guess. If it works perfectly and never goes over a certain temp for MOST of the time.......strange.....

The basic problem can be limited to the temp rise - that causes that pressure rise. 

THIS IS A VERY DANGEROUS SITUATION.

If it was my house, I might install a second aquastat until I figured it out - one that would cut the circuit to the burner (low or high voltage) at 200 degrees or so. Perhaps that reset would at least allow it to cool and then work as you say it does most of the time. A temporary solution, until you get a smart mechanic.

Since you have zone valves, etc. it is really hard to diagnose from afar. Something is very wrong, and my guess is that - if truly everything was replaced, that there is a wiring problem. Water feed does not cause this temp thing. Expansion tank does not cause it either. Circ does not cause it.....and neither does circ.

Isolating the problem is important. The boiler simply should never get above 190 or so, and none of those components have anything to do with it stopping at that temp!

So that's some info, but not all you need.


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## Reggie Dunlap (Dec 15, 2007)

I have no idea what the problem is but be thankful the relief valve worked as designed.


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## webbie (Dec 15, 2007)

The well thing is still a slight possibility......but I suspect other wiring problems. If need be, the well and aquastat might be able to be moved to another location on the boiler, or else that well removed and a new one put in - with the heat exchange grease! But if possible change the aquastat location completely....to rule out some kind of buildup on the inside of the boiler in the well insertion area (far out guess, but possible).


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## Jim Post (Dec 15, 2007)

I would post this thread at heating help .com's "The Wall"  There are many heating pros there that can help diagnose this.


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## antknee2 (Dec 15, 2007)

Do you know if any of the repair men replaced the combination gas valve on your boiler ?? Anthony


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## BrownianHeatingTech (Dec 15, 2007)

Could be a leak in the heat exchanger coil that makes domestic hot water.  That is either located in the boiler ("tankless coil") or in an indirect water heater next to the boiler.

When they leak, the higher pressure in the domestic water leaks into the boiler, causing it to over-pressure.

If the leak is small, the pressure can take a long time to re-build, so it will not happen instantaneously.  It also may be dependent on your water pressure, if it fluctuates (ie, if you have a well).

However, the temp issue makes it seem like the burner is over-running for some reason, which is more likely electrical.  That part-changing nonsense they've been doing is not the way to diagnose a problem.  Replace the expansion tank?  It either is or is not failed, and they can be tested.  Same goes for water feed valves, etc.  You should demand a refund for all that un-necessary work.  Those components can be tested, and there was no reason to replace them if they weren't bad.

Find a service company that isn't populated by part-changing soot-suckers (polite term for hacks like that).  Charging customers for their own incompetence is not acceptable behavior.  Get a better service company, and have them go through the boiler and find the problem.  There are only a couple mechanical things that can cause that, and a few electrical ones.  In any case, that's a simple problem, and a decent tech should have it sorted out easily.

Joe


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## North of 60 (Dec 15, 2007)

Way to go Joe couldnt agree with you more.  She spoke of high temp readings. Bad DHW Coil would only influence pressure.  It almoast seams that the GV is weaping fuel through after its cycle.  Temps were 280 at 90 psi??? Temp and press correspond for steam but it is a residential boiler and should only have a 30 psi relief on it, b/c I know it is not a 15 storey house.  There has to be an exceptional amount of heat in the firebox to maintain 90 psi if it is a properly sized relief valve.  It would sure be nice to step into "puzzled"'s boiler room for a few minutes to catch it in the act re:still flames at the burners when she is reading these temps and pressures.  If her boiler is to code, other than a main temp ctrl, she should have a high limit manual reset that should have tripped to knock the boiler out.  If this was the case, then she has a weeping gas valve on the odd cycle with an improperly sized relief valve.  With the main operator and the manual reset high limit, these high temps that she has been experiencing - could not happen as the chances of two controllers failing is one in a million (unless they are wired wrong  series/parallel).  It is sad in this day and age with all the rules and regs, that she cannot find a competent troubleshooter instead of a guess by golly parts changer!  These people that were "guessing" could have made this situation worse b/c if you do not know how to test a control or device - how would you know how to install it in the first place??  Maybe Puzzled - you should try using someone that does installs in high end residential homes/commercial HVAC control companies that know what they are doing.  And yes $100/hr is cheap when they know what they are doing.  These people that you have dealt with so far give this industry a terrible name and make it hard to justify the wages they charge and what they actually deserve.  Good Luck - NY is too far away for me.  Vancouver, BC Canada was my previous home following behind the people that you just described - cleaning up their messes.  Shameful.


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## antknee2 (Dec 15, 2007)

Probly reading the feet hight on the tridicator not the psi I say the pressure was just ove 30 , the numbers are confussing on residental boilers and sometime not in a readable position . I agree with Joe you should not have to pay for a technitions inexperence .


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## BrownianHeatingTech (Dec 15, 2007)

north of 60 said:
			
		

> Way to go Joe couldnt agree with you more.  She spoke of high temp readings. Bad DHW Coil would only influence pressure.



Most likely.  But a 30-year-old thermaltimeter may not be reading right, so it's still a possibility.



			
				north of 60 said:
			
		

> If her boiler is to code, other than a main temp ctrl, she should have a high limit manual reset that should have tripped to knock the boiler out.  If this was the case, then she has a weeping gas valve on the odd cycle with an improperly sized relief valve.  With the main operator and the manual reset high limit, these high temps that she has been experiencing - could not happen as the chances of two controllers failing is one in a million (unless they are wired wrong  series/parallel).



Depends on code, there.  Our code here in NH only requires manual reset on commercial boilers, not residential.

Joe


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## webbie (Dec 15, 2007)

As brown says, the first thing to do is not to change parts....

The telltale sign here is that fact that it is intermittent. 

My guess with someone who really knew what was going on - two hours and a part or two - maybe $300 - $400 total. $100 an hour is just about right in most places, but for that money you should expect a brain. I do have to "feel" for the technicians when a problem cannot be reproduced though (only happens once in a long while?) - If you can't make something malfunction when you are there, it is very hard to know......what would you do, Brown? (I mean first)....after checking that the expansion works, etc.


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## mikeyny (Dec 15, 2007)

I honestly think someone simply made a mistake. A pressure problem probably occurred, the situation was misdiagnosed, maybe an aquastat was replaced and wired wrong. Happens all the time. It is very rare that a gas valve remains open or slightly open. I would have a confident tech (or some one who can read a schematic) UN-wire the entire unit and re-wire it to original specs. Quite often a simple thing gets overloooked. Start from scratch and fix it.


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## BrownianHeatingTech (Dec 16, 2007)

Testing the expansion tank is first.  And that's _testing_, not just "replace it because you can bill that."

Check the fill valve, too.  Shut off the fill valve and make a note of the boiler pressure.

Check the aquastat versus the thermaltimeter.  If they don't agree, clamp my digital thermometer onto the pipe and find out which one is right and which one is wrong.

If it's piloted, then there's a possibility of a sticking gas valve - I would run it through a lot of cycles.
If it's spark ignited, that can't be the issue because a sticking valve would cause a gas leak, not a normal flame (since there is no pilot to light it).

Check the boiler pressure again.  If it's gone up, then there is definitely a leak into the system.

What was found in the previous tests, and the exact layout of the system, would detail how things went...

I'd definitely put a discharge pipe on that relief valve, too, as that should be piped down to the floor, not aimed across the room.

Joe


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## Gooserider (Dec 17, 2007)

FWIW, and this may not be relevant, we had a Natural Gas hot water heater replaced a few years back, and got symptoms EXACTLY matching the description - minus the non-existent guage readings - Intermittent failure of the pressure releif valve, and also occasional instances of WAY hotter than normal water.

Turned out the brand new heater had a defective gas valve that would intermittently stick on until the relief valve let go - that usually caused enough steam and splash into the area where the burner was to put everything out.  I'd re-light the burner, and the cycle would repeat a few hours later.  

I would suggest checking out the gas valve real closely, and make sure it is RELIABLY shutting off when told to...

Gooserider


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## webbie (Dec 17, 2007)

It does sound like the gas valve from afar. I remember there being recalls of some of these way back - there were some that, when they got wet, they malfunctioned...

Actually, there are numerous such recalls, although yours is probably too old to be affected ......but it simply can be worn out...and therefore not operating correctly.


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## Bartman (Dec 17, 2007)

It is definitely an erratic aquastat, the only way a boiler can reach that kind of temperature is by a sticking control. Once the temp is that high, the pressure follows.


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## Bartman (Dec 17, 2007)

Oh yeah, you have gas, you didn't say what type of burner that you have. An old Peerless may have a fan forced gas burner that functions like an oil unit, or is it built into the boiler?


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