Boiler pressure issues


Old 01-10-14, 05:47 PM
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Boiler pressure issues

I have been having issues with the boiler pressure relief valve discharging water and boiler pressure over 30psi. I had a couple other issues and decided it was time to call a plumber.

Plumber came in and ended up replacing the expansion tank, the pressure relief valve, the air vent (system has only one which sits on top of the boiler) and the zone valve. He brought a fill valve but I opted not to replace that.......that was stupid.

In reading various threads on this forum, I am inclined to think that the fill valve was the problem. Anyway.....

After he left, unit was short cycling and I figured it had an air pocket so I ran water from the zones to try to clear the air and got some bubbles so figured that was the issue. System seemed to run fine for several hours, but then went above 30psi again and pushed water out the pressure relieve valve again.

I called him and he asked me to shut off the water at the backflow preventer and we would see if it keept the same pressue. I opened a valve by the circulator pumb and drained pressue back to 20psi. It kept that for a while and seemed all was fine. Went out for the evening and came back and pressure was at 0. No zones were running. I turned water back on and filled it, but it didn't take much. Started it up and ran it over night with water to fill valve shut off at the backflow preventer. No change in pressure over night.

Turned the water back on this morning and by noon, it was up over 30psi again. Turned water back off, came back a couple hours later and it showed 0psi again. Where is the pressure going?? I could hear what sounded like air or water going past the fill valve even with the water turned off to it. I shut off ball valve before the backflow preventer, the noise stopped.

So is the problem the fill valve or possibly the backflow preventer. The backflow preventer is expensive and I sure don't want to replace that unless it is absolutely necessary. Thanks for any advice!!
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Old 01-13-14, 06:07 AM
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The first thing you should is follow Trooper's directions in the link below.
Old 01-13-14, 07:58 AM
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Yeah, verify that the air charge in the expansion tank is correct and matches the COLD FILL pressure in the boiler.

The pressure may be dropping to zero because when it cools the water contracts, pressure drops... and may be exaggerated if there is TOO MUCH air in the tank.

So check that first, then when the boiler is COOL, like 100F or less, add water until you are at 12-15 PSI and close the manual fill valve. The one that actually works...

So is the problem the fill valve or possibly the backflow preventer
No, NOT the backflow preventer. That can not be responsible for over pressure in a boiler.
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