Furnace pressure valve leaking.


The pressure overflow valve on my furnace is leaking. It's a gas fired hot water radiator system. I recently replaced the corroded original, thinking that that was the problem, but it is persisting. Here are the symptoms: The pressure gauge on the unit shows 30psi which is the burst point for the pressure valve, hence the leak. If I trigger the valve and fill up a bucket with water, I can get the pressure gauge down to around zero, but within an hour it's back up to 30psi. I think the problem may be that the water supply valve to the furnace has failed, allowing water to get by and raise the pressure. Does that sound right? It feels like there's water flowing in the supply line after I trigger the pressure relief valve, but the supply has a ball valve, and I thought those things never failed...Could there be some grit or corrosion in it? I want to make sure I eliminate other possibilities before I cut the valve out and replace it.
Thanks, Andrew
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Andrew wrote:

You could be on the right track.
A HWH Hydronic boiler may have an automatic feed water valve, like: http://www.cashacme.com/a41ab40.php
Or, it may be manually controlled with a valve.
Either way, there could be a leak which is over- pressuring the boiler.
Trace the city water supply line to the boiler and identify all the components. If you are going to replace anything, you'll need a way to shut the supply off. You'll also need to drain the *entire* heating system unless there is some isolation avlve present.
If it can wait, this job is better suited for Spring.
Jim
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I've never seen a furnace with a pressure relief valve. All boilers have them though. Furnaces heat air, boilers heat water or make steam.
Yes, it sounds like your regulator and fill valve are shot. I know of some that are 50 years old and still working, but on my boiler, 7 years is a stretch.
You say the ball vale is in line, but that is probably open for water to self fill if needed. Temporarily, you may get buy turning it off. Unless, or course, that is leaking by also. That can happen
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Thanks for clearing up the furnace/boiler distinction. The ball valve is in-line, and it is definitely closed. It always has been except when I've re-filled the system after draining it. The cold water from the city comes in through this ball valve to a tee that goes *down* into the circulator pump and *up* to supply the radiators. Is this ball valve different from the "regulator" and "fill valve"? Are those two different things or the same thing? Here's the manual for my unit. Figure 5 shows the plumbing configuration:
http://www.crownboiler.com/manuals/content/Residential_Boilers/Gas/Aruba%20 (ABF-SPD,%20ABF-EID).pdf
Thanks, Andrew
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http://www.crownboiler.com/manuals/content/Residential_Boilers/Gas/Aruba%20 (ABF-SPD,%20ABF-EID).pdf
Your system is a little different than mine. I looked at page 5 of the instructions and it looks as though the water supply line is going into a fitting at the expansion tank, or Filtrol tank. If it is typical of most, there is a bladder inside that will absorb the water as it expands when heated. When they go bad they fill up and the bladder no longer moves and you get over pressure.
This shows some of the common parts of a filling system, including the Watts regulator often used. http://www.ccallis.com/expansion_tanks.htm
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Sounds very much as if your expansion tank is full of water. What to do about it depends on the type of expansion tank you have. For mine, I shut a valve leading to the tank, and then there is a valve on the tank that I open to drain out the water. I have a short length of garden hose that I attach to that valve so I can direct the water into a bucket.
CWM
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Okay, I hadn't considered a failure in the expansion tank. Mine is not isolated by a control valve, and there's no way to drain the water from it without taking it off the system, and that would require draining the whole thing. It DOES have a schraeder valve, however. When I activated that valve with my fingernail, air came out and lowered the pressure in the system (as registered on the pressure gauge). And now the leak seems to have stopped and that lower pressure has been maintained. Could this have been my problem all along? Would excess air in the system find its way into the expansion tank and stay there? I guess I'm not sure how that would happen. Any idea what this symptom would suggest? The tank is clearly not full of water, since some air at least came out, but is this a sign of failure nevertheless?
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