Replacing Furnace Press relief valve (Help!)

[timnels]

About a week to go before my house is closing and my pressure relief value went. I got a replacement value at Home Depot. I turned off the water supply that seems to come in to the furnace near the value. I started taking the old value off to replace it and I think the valve is under pressure still (I guess from the gas furnace itself) since once I almost all the way off water started coming out of the joint near the value. Can some one lead me through what else I have to shut off to replace the value? Thanks!

[Speedy Jim]

If this is a hot water (Hydronic) system, you'll probably have to drain the entire system.

Good luck. I think you're biting off a lot.

Jim

[timnels]

Jim, Thanks. It's gas hot water. I am probably in over my head. What do you think a reasonable price to pay someone to replace the value is? Thanks.

[Speedy Jim]

Call around and ask. Prices vary all over the country.

Also.....it's possible the valve is opening because the pressure in the system really *is* too high. This can happen when the water feed valve sticks open.

Jim

[Mike]

Jim, I also have a problem with my hotwater system. I went down to my basement and water was spewing out of the bottom of my pressure reducing valve. I notice that there seems to be a plug which is missing. Are these parts readily available or do I need to replace the whole unit.I am not sure of the model of the valve. Looks like 2 valves in tandem right after the water inlet.

[Speedy Jim]

That's a dual control. First, a pressure reducing valve which is set to maintain a specific "height" of water in the system.

Second is a pressure relief valve which opens when system pressure exceeds (usually) 30 psi.

The relief valve has a discharge port and that may be where water is escaping (as it should).

Typical style:

See what the boiler pressure gauge reads. Normal is 12-15psi (depending on building height, of course). If way over that, the valve may be relieving for good reason. If normal range, the relief valve may be defective.

Jim

[Edwin Pawlowski]

Furnaces heat air, boilers heat water.

Do you have a separate heater for hot water or is it integrated into one unit? If the heater does both, there are two valves, one feeding the hot water, the other feeding the heater portion. Close that valve. There will be some internal pressure that has to be relieved. Put a bucket under the pressure relief and pull up the handle. That takes care of most. When the valve is removed, gravity will still allow some water to flow out.

Not seeing exactly what you have, you probably need some Teflon pipe tape for the threads, a pipe wrench and a large adjustable wrench to open the coupling. Undo the old, put in the new, snug, not overtightened. Slowly open the valve to let water in.

[timnels]

The boiler and the hot water heater are separate gas powered units. I shut off the inlet value that's in front of the water feed pressure valve. I then put a bucket under the pressure relief valve and pulled up on the handle, about 1/2 gallon of water came out fast which leads me to believe the system is still under pressure, yes? That would imply that Jim is right that the whole system needs to be drained? Should I keep draining out the water till it slows, or should I just give up :-) Thanks guys for your help....

[HeatMan]

That's not the only reason.....

[Edwin Pawlowski]

Half gallon is not much. You have the potential to drain all the water sitting in pipes above the valve. If it was under pressure, it would be leaking out rather hard as soon as you cracked the valve or fitting open. Much like a faucet.

[timnels]

Thanks Edwin. Since it's in the basement all the water is above this. Should I try draining some more? It is coming out like a faucet turned on about 75%. _stupid_ question...should I turn the furnace off? The pilot light should stay on, yes? If drain the water out could I damage anything? Thanks again.

[Edwin Pawlowski]

Close the feed to the boiler, then drain

No reason to turn the pilot light off. Thee will still be some water in the boiler so it will not be harmed in any way.

One you refill the system, there will be air in the lines. Someplace there will be a drain, probably in the return line, that you can open to remove the air.

[Phil Yarbrough]

You should call a qualified service technician. Boilers can become dangerous if you don't know what your doing.

[Edwin Pawlowski]

He is working on a water valve, not a boiler. Service technician may not know any more about it that he does. If the OP is not qualified, a plumber would be a better option. I'd agree if he was fooling with ignition systems or flames and gas valves.

[Stormin Mormon]

Retail on the valve plus $50 an hour for labor.

[Edwin Pawlowski]

[Stretch]

You may have a waterlogged expansion tank or a diaphram tank with a ruptured diaphram. If that is the case, replacing the relief valve won't help. You may also have a bad water feeder. You may have a bad relief valve. Those are the most likely problems.

Stretch

[timnels]

Beating a dead horse here. The gauge on the side of the furnace says

21 PSI with a temp of 100. SInce I have the water intake shut off and water isn't spewing out the pressure relief valve can I assume the pressure relief valve is OK?

[Stretch]

In that case, it sounds like a bad water feeder or waterlogged expansion tank or ruptured diaphram in your expansion tank.

Stretch

[Bobby_M]

I'm going to agree. I've had the same issue with two previous heating systems and it was the expansion tank diaphram both times. Yes, the first time it happened I replaced a perfectly good over-pressure valve. The tank is cheap enough to replace and if you're lucky, there will be a shutoff valve right at the tank so you don't have to drain anything nor rebleed the air out after.

Bobby