Leaking Pressure Relief Valve

[Gary in NJ]

I've seen the Pressure Relief Valve on my boiler blow-off in the past due to to excess air in the system (failed automatic air bleed) or a failed expansion tank, but over the last week the BOV/PRV has been leaking for no reason that I can detect. It's a 30 psi valve and I run my system at 12 psi. Any ideas on what I might check.

 

[Dana]

Checking the pre-charge level on the tank is the first order of business. If the schrader valve is leaking air slowly it may be losing charge, even though the tank is still good. Tightening or replaceing the schrader valve usually fixes that.

 

[Sponsor]

 

[Gary in NJ]

Ah...I always leave it open so air can escape. I'll tighten it and see if things improve. When should the valve be opened? Is it only when purging air from a loop?

 

[Dana]

The schrader valve is the same as an automotive tire valve, where you pump up the expansion tank to the desired system pressure (or a very few psi higher) prior to pressurizing the system. Any valves that can isolate the tank from the system need to be open when the system is operating.

 

[Gary in NJ]

I can say with certainty that I've never checked that. The expansion tank rings, so I know the bladder isn't compromised. The tank is a Watts EX-30 that has an install pressure of 12 psi and a max working pressure of 75 psi. The problem is, it's installed and in service? How would I check the pressure to get a usable reading? What psi should I fill to?

I did check that the valve was tight. The current psi is at 10.5. Since I run this system at 12psi, should I see 24 psi at the tank?

 

[Dana]

There is hopefully a valve isolating the tank from the system.

Turn off the power to the boiler.

Turn off the isolating valve, then unscrew the tank until you see water begin to dribble. If the system is going to be operated at a nominal 12 psi, pump up the air side of the tank to 12 psi minimum , 15 psi maximum. That should force more water to dribble as the air pressure pushes diaphram into the water side of the tank.

Give it a few minutes for the pressure to stabilize as the water is pushed out, or unscrew it another 1/4 turn to speed things up. Recheck the charge pressure and adjust as-needed. Then screw the tank back on tight, and open the valve to the system before re-starting the boiler.

 

[Jadnashua]

The pressure (from the water side) needs to be relieved before you can test and charge the ET. Once it's back in service, the air pressure will equal the water pressure once the water starts to expand.

When done, if you don't have a good cap for the valve, go buy one and install it. The Schrader valve itself doesn't always seal perfectly, and a good cap will have a rubber seal in it to help ensure the valve doesn't leak.

 

[Gary in NJ]

Problem solved. Something new to add to my annual maintenance. Thanks.