Over Pressure valve dripping

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Old 02-04-12, 08:22 AM
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Over Pressure valve dripping

Hello,
My heating system, has been dripping water out the over pressure valve lately. The bucket under the valve seems to always have water in it. The boiler pressure is at 27 when running yet the valve drips very slowly. How do I change this valve out? After turning off the boiler, what is the best way to reduce pressure to be able to remove the valve? I have on occasion see the boiler pressure higher than 30 psi. It is not at that pressure today. Looking at it before it was 27, and has a slight drip from the valve.

On another note, we here the sound of water running into our upstairs baseboard when the zone valve opens. Is it normal to hear the water entering the baseboard? I don't recall hearing it before. I just remember hearing the metal making heat expansion noises.

Thanks in advance,
Ken



 
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Old 02-04-12, 08:33 AM
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I believe the recommended replacement interval for that pressure relief valves is every five years.

Allow the boiler too cool off to about 100 degrees. Close the valve to the make up water. If you have them, close the valves to the supply and return pipes for all your zones. You will have to drain the water out of the boiler through the boiler drain. You need to get the water level below at least below the level of the valve.

This is a perfect time to check the air charge in your expansion tank. It should be 12 psi. If water comes out of the schrader valve, then you know it is toast and needs to be replaced.

The sloshing of water is an indication that there isn't enough pressure in your system. You said your gauge indicates 27 psi and higher. I have a feeling the gauge may be bad. Your system should be a minimum of 12 psi when cool. It will increase in pressure when the water is hot, but typically not higher than 20 psi.
 
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Old 02-04-12, 08:33 AM
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Your pressure is too high. Changing the relief valve won't help.

Excessive pressure can be caused by a water-logged expansion tank or the automatic fill valve leaking past the seat. Post some more wide-angle photos so we can see how the whole thing is piped.
 
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Old 02-04-12, 08:47 AM
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Old 02-04-12, 09:04 AM
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Ken, while it may actually be advisable to change out the relief valve, it is NOT the root cause of the trouble.

As Gilmorrie has stated, there are two possible problems, the tank, or the fill valve. The first thing to do is to check the tank.

[there is actually one more possible cause, but it is remote, so we'll only get to that if the first two things don't help. 99% the problem is your expansion tank]

Here are step by step instructions for checking/servicing the expansion tank.

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.
The air sloshing sounds that you hear are a result of the pressure problem, and we'll get to that after we diagnose what's causing the pressure to fluctuate. So check the tank first.

HD and Lowes sell the tanks, about $35 or so. Make sure to get the type for HEATING SYSTEMS, not the ones for domestic water heater!
 
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Old 02-04-12, 09:16 AM
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By the way, in case you are ever tempted to service the pressure tank on your well system, this procedure does NOT apply to that one as well... similar, but not the same.

This type of pressure tank, both the heating and domestic water do normally lose a PSI or two of pressure per year. They should be checked at least every two years. If your well pressure tank has not been checked in more than two years, you probably ought to do that...

With either of these types of tanks, you can NOT properly check the air pressure in the tank if there is ANY pressure on the water side. This is the reason for dropping the boiler pressure to ZERO in the previous instructions, and for your well system the same rule applies. You must turn off your well pump, open a tap and let the system de-pressurize. Leave the tap OPEN and set the air charge in your well tank to TWO TO THREE PSI BELOW THE LOW PRESSURE CUT-IN of your well pump.

I know the well tank bit is off-topic, but it's wise to check it. If you wish to discuss the well tank further, we can continue that over in the water well topic, let me know.
 
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Old 02-04-12, 09:22 AM
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In the second picture you posted, on top of the boiler, next to where the circulator pump is bolted on, there is a small brass can with a cap on top. That thing is an 'automatic float type air vent'.

I see what appears to be mineral deposits on top of it indicating that it has been leaking.

Is that cap screwed down tight? If it is tight, does it leak water when you loosen it?

If it leaks water when the cap is loose, then it is defective and should be replaced.

In normal operation that cap should be left loose. As air accumulates in the can, it is vented to the atmosphere automatically.
 
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Old 02-04-12, 12:10 PM
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Thanks ie relief valve

Thanks for reply. I will check this out and post back. also why is the valve leaking at 27 psi when it is designed to open at 30?
 
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Old 02-04-12, 12:42 PM
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There is a certain 'tolerance' to the accuracy... of the valve, AND your gauge. Your pressure gauge may not be that accurate, and the valve could be a little off too...
 
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Old 02-04-12, 04:45 PM
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why is the valve leaking at 27 psi when it is designed to open at 30?
As Trooper indicated, we don't really know the precise system pressure when your gauge reads 27 psi. But, if the relief valve snaps totally open at exactly 30 psi, don't you think it might start simmering a bit below that pressure?
 
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