Pressure relief valve leaking

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  #1  
Old 02-21-12, 03:29 PM
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Pressure relief valve leaking

I'm new to these forums and am in need of some help.


I have a leaking pressure relief valve on my furnace. I thought it was the valve itself because it was almost 10 years old and a bit corroded. But after trying 2 different ones the results are the same.

The system pressure is 12 psi cold and rises to 20 psi when hot. The furnace shuts off at 180 degrees so its not getting too hot. but the problem still persists.

Is it possible the auto feed valve is bad? I turned off the valve feeding it and the leak was almost gone. BUT it still dripped a little bit. I thought that if these valves went bad the pressure would be too high.

Anyone have ideas? I'm getting a little tired of emptying buckets.
 
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Old 02-21-12, 03:34 PM
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The system pressure is too high. Probably the gauge is in error? Possibly, the expansion tank is water-logged, too? Yes, if the auto feed valve is leaking past it's seat, that can cause excess pressure.
 
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Old 02-21-12, 03:38 PM
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By the way, when a relief valve discharges, 9 times out of 10 the problem is not with the relief valve itself - it is discharging because the system pressure it too high. Don't replace that relief valve again.
 
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Old 02-21-12, 04:01 PM
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The pressure is not too high. When I shut everything down the pressure drops to zero. When I open the supply valve the pressure rises to 12 psi and moves to 20psi when the furnace heats up. So I'm pretty sure the gauge is working. Thats what has me confused. Also is it possible that if the autofeed valve is bad it can "over fill" the system causing this problem without causing too much pressure?
 
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Old 02-21-12, 04:42 PM
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Its probably going higher then 20psi but the gauge is faulty and its getting stuck there.

Does it ever go past 20psi?

Your best bet is to make a gauge to verify that one is accurate.

Once you determine that then you can take steps toward the cause and repair. ( which would be expansion tank or fill valve)

Get something like this that attaches to the boiler drain.





Next time you get the pressure to 0 in the boiler check the air charge in the expansion tank.

Also next time you fill the boilerfrom 0 psi put 12 psi in then shut the feed off.

Make sure boiler is cool.






Mike NJ
 
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Old 02-21-12, 04:44 PM
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It is very possible for a gauge to be 'non-linear', or get STUCK at the high end. Relief valves are robust little gadgets, and if it is opening, you can be fairly confident that the pressure is very close to 30 PSI.

VERIFY YOUR GAUGE, or spend time and money CHASING GHOSTS! ( I just looked at your nickname... I believe you are in a good location to chase ghosts! OH! the HORROR!)

There's a 'sticky' message at the top of the list that tells how to make a gauge. The one that Mike showed has too high a range gauge to be useful down at 10-15 PSI.

Click and read:

http://www.doityourself.com/forum/bo...ure-gauge.html
 
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Old 02-21-12, 04:46 PM
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The pressure is not too high. When I shut everything down the pressure drops to zero. When I open the supply valve the pressure rises to 12 psi and moves to 20psi when the furnace heats up. So I'm pretty sure the gauge is working.
OK, then why is the relief valve lifting? If, when you "shut everything down," whatever that means, the pressure goes to zero - that indicates something is wrong. Please go back and read the previous posts.
 
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Old 02-21-12, 04:51 PM
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Absolutely do NOT ASSUME that gauge is good! Time and time again we have seen this problem...

When you find that the gauge is wrong, you will next be servicing your expansion tank. That is a given.

What type of tank do you have?

Does it look like a propane tank from a gas grill hanging on a pipe? Or is it a large steel tank strapped into the joists above the boiler?
 
  #9  
Old 02-21-12, 05:41 PM
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The expansion tank is an Extrol Model 30. I'm going to get the parts together ASAP and make a gauge. At least I can verify if the gauge is working.
 
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Old 02-21-12, 07:04 PM
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Ray, how old is the tank, and how long has it been since the air charge was last checked?

Those tanks are about $35 or so... if you do buy a new one, be sure to get one made for heating systems, not for potable water... they do make both kinds, and HD or Lowes will probably have both on the shelf.

Is the tank HANGING from the pipe? ( not standing on it's head, or sideways? )
Is it mounted to an 'AIR SCOOP' ? (big cast iron part)
Is there a brass 'can' on top of the air scoop? with a 'tire valve' on the top?

If you want to make it easier to service the tank in the future, you can add some optional valves when replacing in order to make it a simple 5 minute job to check the air charge. The procedure below need not be followed then:



What this will allow you to do is relieve the pressure on the tank in order to check and charge the air without having to drain anything from the boiler. It also allows tank change easily.

You can make up that part with black steel threaded fittings, no soldering needed. You will need :

2 short 1/2" steel nipples
1 1/2" threaded ball valve
1 1/2" tee fitting
1 1/2" boiler drain (1/4 turn type is best)

These tanks should have the air checked and charged at LEAST every two years as they normally lose 1-2 PSI per year, just like car tires do!

Here is a step by step procedure for checking/charging that tank with air.
If the tank is standing on it's head, the bit about the water coming out the valve may not happen, even if the bladder is broken!

-----------------------------------------------------------------------------

1. Shut off boiler and allow to cool to under 100F.

2. Shut off water supply line to boiler.

3. Drain only enough water from the boiler drain to drop the system pressure to ZERO. REPEAT: DO NOT COMPLETELY DRAIN THE BOILER! ONLY ENOUGH TO DROP THE PRESSURE TO ZERO!

4. With an ACCURATE tire pressure gauge, check the air charge in the tank on the air valve opposite the end of the tank that's connected to the system. If ANY water comes out of the air valve, the bladder inside the tank is shot and the tank needs replaced. If no water comes out the air valve, and the pressure is less than 12-15 PSI, continue to step 5. If the pressure is OK, turn the water supply to the boiler back on and repressurize the system, turn the power back on to the boiler, no service is necessary.

5. Using a bicycle pump, or a small air compressor, add air to the tank until you have 12 PSI air charge.

6. Check the boiler pressure gauge again, and if it has risen off ZERO, drain some more water from the boiler drain until it is again at ZERO.

7. Check the air charge on the tank again. If it is below 12 PSI, add air to the tank until it is at 12 PSI.

8. Repeat steps 6 and 7 until the boiler stays at ZERO and the tank stays at 12 PSI. At this point, the tank is properly recharged and the water supply can be turned on to re-pressurize the system, turn the power on to boiler and return to service.

----------------------------------------------------------------------------
 
  #11  
Old 02-22-12, 09:18 AM
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The tank is hanging down from the air scoop. Its about 10 years old and I've never checked the charge. I'm hopeful that its the cause. Im going to check the the system pressure with an external guage I just made. I'm starting to believe its the cause because it only leaks when the system is heating up and the water is expanding. But only after I'm sure of the pressure........ Thanks for the info. I'll let you know the results.
 
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Old 02-22-12, 09:54 AM
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I'm quite certain that you will be replacing that tank. Might not be a bad idea to just pick one up to have on hand when you start working... then if by some slim chance you don't need it (very slim chance!) you can return it.

If/When you do replace the tank, even though they are pre-charged from the factory, it's a good idea to check the pressure before you install it.

One more thing to know: If that tank has failed, it will be full of water when you remove it. It won't feel heavy as you spin it off the air scoop, but BE PREPARED! for the weight! It could weigh around 30 pounds. You don't want to break a toe (or worse!). Don't be deceived by the light weight of the new, empty tank.
 
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Old 02-22-12, 01:33 PM
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I checked the system with an external gauge that I made and sure enough the pressure rose to above 30 psi. I checked the charge in the expansion tank and there was 2-3 psi at the most and NO water came out. I followed your procedure on how to recharged the tank and everything is GREAT!!! When the furnace heats up the gauge now reads 18-19 psi and no more leak! I'm going to keep an eye on things over the next few days to see if the expansion tank loses its charge and the problem comes back, but I'm pretty sure that it just slowly lost its charge over the years.

I learned a couple of things here. First, I never realized that the expansion tanks can just lose its charge over time. Second, I can't believe how easy the problem was to fix...... And third and most of all NEVER ASSUME THE GAUGE IS CORRECT!! Thanks everyone. You saved me some money and one more headache is gone!
 
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Old 02-22-12, 02:47 PM
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My Mantra when I meditate... uhhh, I mean drink beer... is:
"never trust a boiler gauge... never trust a boiler gauge... never trust a boiler gauge... "

I'm pretty sure that it just slowly lost its charge over the years.
Probably so. There's a problem though when tanks are not serviced regularly that the rubber membrane inside gets stretched out into a 'non-design condition'. It may last, but it may not. Yep, keep an eye on it. If the problem returns, just replace the tank, and throw those optional valves at it.

Good Luck!
 
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