High Boiler Pressure


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Old 12-02-08, 04:43 PM
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High Boiler Pressure

I have a standard Burnham oil fired hot water heating system with 5 zones plus a hot water heater zone. It is 20 years old with no recent changes. The PRV started popping off a few weeks ago and I replaced it but still having high pressure issues. When running, the boiler pressure hangs around 15 to 20 psi but after running for a while the boiler temp and pressures typically raise together to round 185 -190 F and 30 - 32 psi (although some times the pressure raised to 30+, with temps at 140. The auqastat setting is around 195 F. Does not appear to be any excessive air in systems and the bladder tank appears to be ok with warm on top cold on bottom. The tank pressures track with the boiler pressures at about 10 – 12 psi when cold to 30+ when hot…. although I could not get a reading from the tank at last check – nothing came out with the boiler hot. To rule out the pressure reducing fill valve I shut the water feed line off and ran the system for a while but the temp and pressure still rose with drips from the PRV. I even tried popping the PRV while the fill was closed and the pressure rose back instantly. I have also tried isolating the domestic hot water tank and still have same issues with rising pressure. What am I missing?
 
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Old 12-02-08, 04:53 PM
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Tank Pressure

The tank pressure needs to be checked with the system pressure at zero, otherwise you are simply checking the higher of the system pressure or tank pressure. If you find the tank pressure to be low (normally +/- 12#) add air with a hand pump or small compressor.
 
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Old 12-03-08, 02:52 AM
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Thanks, I did check the tank when cold, drained some water off boiler to 0 psi and checked tank – it was low (I think because I checked it so many times). The isolation valve to the tank is frozen so could not shut off. I added some pressure to bring it back to12psi. The boiler pressure is still rising to higher than 30 psi.
 
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Old 12-03-08, 03:59 AM
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I just looked up the Amtrol Extrol web site and it suggested not installing the tank on a dead-end line as air can collect and cause corrosion.. Mine is, but has been this way for 20 years so assume that is not a factor....although the tank does look much newer than the boiler – I have only lived here for 6 years.
 
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Old 12-03-08, 07:35 PM
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I recently had a similar issue - the high pressure was caused by a bad expansion tank.

If you open up a drain below the tank, what color is the water?
 
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Old 12-03-08, 07:55 PM
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Expansion Tank

With the isolating of the domestic & shutting off the feed water, the only thing left which would cause a pressure rise is the tank. When you pumped it back up, the boiler pressure increased as well. Did you let the pressure off the boiler & re-check the tank? If you didn't you could be missing a tank problem. Another thing you can try is using soapy water on the air valve of the tank to check for an air leak there.
 
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Old 12-04-08, 08:38 AM
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Tank

How do I check the air pressure in the expansion tank? I don't see anyplace to check it?
 
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Old 12-04-08, 02:37 PM
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Mkdsk

Bladder type tanks have a "tire valve" for checking/adjusting the air pressure. If you have a conventional tank (long, large, & usually strapped to the floor joists) you probably won't have any way to check the air pressure.
 
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Old 12-07-08, 12:40 PM
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Yep, it was the tank. I guess I made a few assumptions to quick and too early about the old tank. Tank was only 25$ at Home Depot, valve to isolate tank so next time I don’t have to drain entire system $6, help from this forum priceless.
 
 

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