Auto fill valve left closed after repair?

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rural_engineer

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I had a pump go out on my boiler a few weeks back. My oil company came out and replaced it. Just recently, I noticed that my attic office was getting cold. I tried to bleed the radiators, figuring that there was some trapped air that worked its way into the attic after the repair.

The bleeder hissed for a moment, then stopped with nothing coming out. I went down to the basement, poked around, and found that the ball valve leading to the auto filler was closed. I opened it, and the system pressure popped up to 25 PSI. I bled the attic radiator, and everything seems to be working now.

Here's my question: Is there any reason that ball valve would have been left closed? Do I need to check anything after doing this?
 

Fitter30

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There are two schools of thought. One if there a leak only the system water will come out. The other with open fill it would be a flood. After replacing a pump or a major repair where the system would be drained my preference would leave the fill on for a few days let the bleeders do their thing then turn it off. But all depends what type of air removal devises your system has. Some are more prone to stick and leak. System pressure and the expansion tank. Most systems run at around 12 lbs with pumps and boiler off. With boiler and pumps on boiler up to temp pressure may rise 3 - 4 lbs just depends on type of expansion tank and size. Most systems use a bladder tank looks similar to a lp bottle for bbq. It will have a plastic cap on the opposite side of the pipe connection that has a what looks like a tire valve to measure air pressure in the bladder. If system pressure gets to 25+ lbs ex tank needs to be checked out.
 

rural_engineer

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My conclusion is that the people who came out for the repair were only interested in getting the pump swapped and didn't care that the boiler was one glitch away from venting.

1. When the boiler got hot, it was nearing 30psi
2. The auto-fill valve was set for 25psi
3. The expansion tank was at 4psi after I drained it. (I even asked whether the expansion tank was properly charged while they were here.)

I upped the expansion tank precharge to 14psi.
I dropped the auto-fill pressure to around 16psi (The house is 3 stories + basement)
The boiler is sitting around 20psi when its hot.

I'll leave the auto fill on for a few days, bleed the attic again, and see how things go. Does that all seem okay?
 

Reach4

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Here's my question: Is there any reason that ball valve would have been left closed? Do I need to check anything after doing this?
Yes, I have read people suggest that. It prevents a small leak in the fill valve from overfilling, and making the pressure relief dump water. I have no relevant experience. Fitter30 has a lot of good experience.

If your water drops with that valve closed, check your thermal expansion tank. It may have failed. It will normally be empty of water. When you knock on it, it will sound hollow. The air precharge should match the cold water pressure, where the autofill valve would have charged you to. That maximizes the ability of the tank to absorb expanded water, preventing the pressure from rising so high that water is lost from the pressure relief.

If the autofill valve can fill, a bad expansion tank will cause loss of water thru the pressure relief. That brings in new water, which will contain oxygen. Oxygen is a given for the initial fill, but you don't want to keep adding more.
 
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