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
You could be on the right track.
A HWH Hydronic boiler may have an automatic
feed water valve, like:
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.
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
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
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:
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.
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.
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
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