Furnace always building pressure

Hi,
I put a new pressure relief valve on my furnace and re bleed the system. Ever since then, my furnace is building pressure. I drain a little water and it goes back down. I did this about 5 times in 2 days Last year I put a new expansion tank on and a new boiler feedvalve. .
Any ideas on what my problem may be.
Thanks
Dennis

DID YOU correctly drain the exp. tank?





R

No I did not drain the expansion tank. How do I do that?

ODDSNENDS4U wrote:No I did not drain the expansion tank. How do I do that?

Depends, what type of exp. tank do you have?





R

I am assuming that you have the older style expansion tank up between the joists, and not the newer rubber ballast type tanks that usually mount to the air scoop. If that is true, you shut off the expansion tank feed valve, and usually there is a bleeder valve hooked up to drain the tank. Sometimes it is a plug, sometimes a valve. There is pressure within, so don't do anything stupid.....hot or cold water comin' your way.

My pet peeve: You DO NOT have a furnace. You have a BOILER! Furnaces distribute warmed air, boiler distribute steam or heated water. I don't understand how the h..l folks get this confused, but many do. I'll stop ranting, all I really want to do is get you back operational.

Another thought is that you might have a pinhole leak in the HW coil. How high is the pressure going up to?
Obviously it isn't above 30 psi or the PRV would blow off.
If you can drain the pressure down to 15 psi, and have it stay there unless it rises when heated up, the problem sure seems like an expansion tank issue. Good luck, Mr BOILER man.

It is a Honeywell welded exp tank model tk300 60 butyl diaphram 7.4 cap precharge 12 psi
Thanks
den

LOL My boiler water water heater 520 efm has an expansion tank with a valve stem on the end

Well, it doesn't sound like it is the expansion tank since it is a diaphram model. It could be what whistle nut said, a pin hole in the domestic coil. Is it a new boiler or an old boiler? You have to start troubleshooting somewhere. That new feeder valve you put on could be bad. Tonight, when everyone is done using domestic hot water, drain some water out of the boiler to a set point, say 15 pounds, and shut the valve off that supplies the domestic coil. If the pressure remains the same, the coil is the problem. If it goes up, it is probably a fill valve. Only two things put water in the boiler, the coil if it is bad or the fill valve if it is bad. Don't forget, the fill valves are adjustable.

R

My PRV is letting off also and last I checked the pressure was at about 38 psi. So I drained a little water to bring it back down to 20 psi
Den

OK I drained it down to about 15 psi and I shut the valve that feeds the domestic hot water. Now I wait and see if the pressure stays the same or goes up?
Thanks
Den

Is it ok to leave that cold water valve closed all night?
Den

Hi,
With the cold water domestic feed valve closed, The pressure still went up!! Now is it the taco fill Valve?
Den

Looking like the fill/backflow valves are not working correctly, or have some crap stuck under a seat allowing water to bypass the fill valve. If you are sure that the domestic water is off and a valve is not leaking by, then it has to be the fill valve area. Are the domestic hot water valves ball valves or stop and waste valves? (We hate stop and waste valves, you need full port valves or you compromise the flow dynamics). Glad you found that boiler, too!

Hi,
It is a ball valve on the domestic feed. Do you think I should take the taco valve off and see if I can clean it?
Or just replace it? Are they expensive?
Den

I'd try to clean it first. The fill valve alone is about 28.00. The fill and backflow is about 60. It could be just a piece of sand or rust.