Oil Fired Boiler Exceeds 30 PSI Pressure

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baldy54

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Weil-Mclain Boiler 10 years old no problems til now. Burner comes on Pressure goes to about 32psi, very shortly. Have never had to bleed for air as it seemed to do very well with the Spirovent. Checked the Expansion tank tapped the valve and air came out, the top of the expansion tank gets slightly warm as though no hot water had entered the tank. The only thing that was done is the service people replaced the oil filter and replaced the burner nozzle just within the last 30 days. Any ideas why the 30psi is being tripped? Thanks for any help.
 

Reach4

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Checked the Expansion tank tapped the valve and air came out, the top of the expansion tank gets slightly warm as though no hot water had entered the tank.
You might set the precharge in the pressure tank. With the water pressure at zero, the precharge air should be at or a little above the pressure where water gets added.

Also, when the water pressure is zero, knock on the tank to check that it sounds empty.
 

baldy54

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You might set the precharge in the pressure tank. With the water pressure at zero, the precharge air should be at or a little above the pressure where water gets added.

Also, when the water pressure is zero, knock on the tank to check that it sounds empty.
I am waiting until next week when the weather is supposed to get up in the 70's just incase I do something to screw it up. Shouldn't the expansion tank get warm so that you know water is going in there when the PSI is up at 30? Overnight I get about one and a half gallons in the bucket I use to catch the overflow. If it turns out to not be a expansion tank problem, what else could be causing me grief? Wrong Nozzle, Circulator Impellors worn out, that is all I can think of. The Spirovent has worked very well over the 10 years no crackling or signs of air in system maybe an expansion creak some time that I hear.
 

Jadnashua

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IF the precharge on the ET is way too high, the pressure will rise until it equals that in the ET before the bladder can compress. While there shouldn't be, is there a valve on the inlet to the ET? If so, are you sure it is wide open? If the system has been leaking, and fresh water has been added on a regular basis, and (that's lots of IF's!) you have a steel nipple or fitting to the ET, it could be internally clogged with rust, preventing the ET from functioning.
 

baldy54

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There is a small steel nipple just before the ET. I don't understand how the pressure in the ET could have increased. Of course that does
not mean that it did no increase. Will start by turning off the water, pop the safety valve to release any pressure and then I guess I will
check the pressure in the ET, don't have an accurate gauge for that. May try a tire gauge. The clogged inlet to the ET is a good candidate for being the problem.

Better thing to do is drain the system check the steel nipple and buy a new ET, I guess. If the weather stays as nice as they say I should be
able to figure out what is going on. Turned power off and shut off the water to the house, the water pressure to the furnace is approx. 9-10 psi, will wait to see if the pressure drops and to prove if there is a leak somewhere in the system. If the pressure holds, my next step will be to drop pressure to zero and take a reading of the ET.

UPDATE: I did a reading of the ET and it was almost up to 28PSI. How did that happen? Reduced pressure to about 12PSI and am now turning the Boiler on to see what happens.
Boiler turned on pressure went up to about 21-22 psi it held there and it turned off at temp.
set. It had been about a 1/2 hour and the pressure is still at 21 psi should it slowly bleed back down to 10-12 psi??
 
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Dana

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As the water in the system cools off, it will shrink in volume and the pressure will drop. A half-hour of standby loss on a boiler isn't going to be enough of a temperature difference to change much, if a large fraction of the system water is in the boiler (as is often the case with fin-tube baseboard coupled with cast iron boilers.)
 

baldy54

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As the water in the system cools off, it will shrink in volume and the pressure will drop. A half-hour of standby loss on a boiler isn't going to be enough of a temperature difference to change much, if a large fraction of the system water is in the boiler (as is often the case with fin-tube baseboard coupled with cast iron boilers.)

Thanks for responding. The inlet pressure is about 10psi and since I took the 28psi out of the ET down to about 10psi, when the burner comes on the
psi goes up to 21psi and yes it drops back to about 10 before the burner comes back on. I can tell that the hot water is going into the ET and keeping the pressure below the 30psi valve. I still can't understand why and how the ET pressure got up to approx. 28psi ? When it is supposed to be 12psi.
 

Jadnashua

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It sounds like your ET may be undersized for the volume and temperature range of your system. For maximum longevity, you don't really want the bladder to have to move all that much. While the pressure may go up some, with an ET optimized for your system, it should not rise from 10-21psi unless it is too small, or your fill valve is leaking and letting more water into the system.
 

baldy54

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It sounds like your ET may be undersized for the volume and temperature range of your system. For maximum longevity, you don't really want the bladder to have to move all that much. While the pressure may go up some, with an ET optimized for your system, it should not rise from 10-21psi unless it is too small, or your fill valve is leaking and letting more water into the system.

It has worked okay for 10 years. The max temp is set at 180 and the lift is from the basement to the first floor. The fin baseboard is heating about 1400 sq feet. When you say the fill valve is leaking, do you mean that it is allowing more than the set value into the boiler? What about the hot water
coil in the boiler could it have any affect on the pressure increase? Like if it had a pin hole etc?
 

Leon82

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He means the regulator is letting water in even though it should not. It could be worn or corroded.
 

baldy54

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He means the regulator is letting water in even though it should not. It could be worn or corroded.

Thanks Leon

Just did a little thought on the subject. If the valve is leaking wouldn't the pressure show more than the 10 pound static value? Maybe I am not correct in my thinking but I am not standing in front of the boiler. Might change my thought as I look at the boiler and the valve.
 
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Jadnashua

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If the autofill valve is defective, just sitting there, the pressure could rise. An ET can last a long time, they'll last longer if they are sized properly. There are at least a few sizing calculators out there, but you need to know or calculate some entries to get a good result (water volume, temperature deltas, etc.).
 

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What would be the normal operation of a boiler that shows 10psi cold. What would be a normal PSI for the boiler after it shuts down after a burn cycle?
 

Jadnashua

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I have a mod-con, and the pressure only varies a few tenths of a pound from cold (room temp) to its max, which is a bout 194 when heating the indirect. Normally, it runs about 130. These tend to only have a fairly small volume of water in the system, so my ET is fairly small, but sized properly. So, given typical room temp, I can see temperature swings of 120-degrees, which is probably more than many boiler out there, and my pressure is essentially stable.
 

baldy54

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I am still searching, how come the ET pressure supposing to be 12 psi was up at 28 psi? Checked it with the boiler pressure at 0 psi.
 

baldy54

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I am still searching, how come the ET pressure supposing to be 12 psi was up at 28 psi? Checked it with the boiler pressure at 0 psi.

I think I will do this: Since the winter is over and I only use the boiler for hot water, I am going to shut it off. Drop the pressure to zero and see
what the pressure builds up to. If the pressure goes above the 10 psi that will be an indication that the fill valve is leaking. What do you think?
 

CappA

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Strange, the 28 psi in the expansion tank if the boiler pressure reads 10-12 psi. But I suppose that pressure wouldn't really affect the system pressure when idle.

I'm following this thread whereas I have some major pressure fluxuations as well, with blowoffs that release more as nuisances with little water but needing a pail to catch it.
It's always under pressure, have replaced 2 faulty expansion tanks, and I have an external domestic Boilermate. Never a domestic coil in the boiler itself.
Also have an add-on wood boiler (the reason for 'expansion tanks', plural) that overheated a few times before understanding how to better control the nature of the beast. A couple of overheatings cooked the expansion tanks at the rated 230*F. Everything else seems functioning normally.
I think I'll try purging the system again on the next warm day, whereas it was recently that I replaced the ETs and maybe it's air remaining in the system.
 

baldy54

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I have not done the test that I eluded to above. Want to be sure I can turn off the boiler and make repairs if needed. The pressure stays at about 20 psi and it does not seem to come down to the 10 psi it should.
 
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