Boiler identification and PRV

You can try flushing the relief valve out by opening it a couple of times in hopes that it will flush out any debris that may be holding it open. If that doesn't work, then you either need to replace the PRV (they're not terribly expensive) or adjust your system pressure so that it runs at something like 15 psi instead of 30. If pressure is the problem (i.e., it gets up to 30 psi) What kind of expansion tank do you have? Do you know if it's working properly?

30 psi is standard in this country, as far as I know. That's what you should go with. Don't confuse it with a domestic hot water PRV, which looks similar and will fit, but the pressure is much too high. You should have a pressure gauge somewhere on your boiler that will show you what the pressure is at any given time. They're cheap and not hard to install, so if you don't have one where you can see it, by all means, have one installed. Any 1/2-tap into the boiler or its piping will work. As I said, your system pressure at the boiler should be around 15 psi--maybe slightly higher when it's hot.

The fact that your PRV starts to drip when you bring the system up to temp tells me that you have a problem with your expansion tank. If it's a more modern (read: small) tank, then it's probably a bladder tank and the bladder may be shot, which would allow the system pressure to rise as the temp increases. If you have an older (read: big, hanging from the rafters) expansion tank, then it's probably full of water and needs to be drained for it to work properly.

Either way, it doesn't sound like a serious problem, but you should get it fixed before the heating season begins in earnest.

Around here PRV is usually an acronym for Pressure Reducing Valve, relief valve is usually called just that. Around my parts anything over 30psi is considered high pressure and requires addition inspection. Any residential relief valve should be set at 30psi. Most systems should be running in the 10-20psi range. If you relief valve is dripping there are only a few things that could cause this. Relief is bad (should be changed every few years anyway) Expansion tank is bad (bladder gone), or waterlogged (common of the older galvanized/steel bladerless tanks usually hanging from the ceiling), your waterfeeder could be bad and overpressuring your systme (this is the valve that allows water into your heating system, and should be set at or around 12psi. I always turn mine off after filling, if your system needs water after the fact it has a leak, install a LWCO and close the waterfeeder after initial filling in my opinion) Other than that you could check your tankless coil or indirect water heater coils for leaks, its rare but it does happen.

Where are your circ pump(s) on the boiler supply or return?

Morgan said:

Around here PRV is usually an acronym for Pressure Reducing Valve, relief valve is usually called just that. Around my parts anything over 30psi is considered high pressure and requires addition inspection. Any residential relief valve should be set at 30psi. Most systems should be running in the 10-20psi range. If you relief valve is dripping there are only a few things that could cause this. Relief is bad (should be changed every few years anyway) Expansion tank is bad (bladder gone), or waterlogged (common of the older galvanized/steel bladerless tanks usually hanging from the ceiling), your waterfeeder could be bad and overpressuring your systme (this is the valve that allows water into your heating system, and should be set at or around 12psi. I always turn mine off after filling, if your system needs water after the fact it has a leak, install a LWCO and close the waterfeeder after initial filling in my opinion) Other than that you could check your tankless coil or indirect water heater coils for leaks, its rare but it does happen.

Where are your circ pump(s) on the boiler supply or return?

Click to expand...

+ Word

One other thing that just crossed my mind, I was on one of the few service calls that I do for a problem just like this one. Couldn't figure out what was causing the system to over pressure and weep at the relief valve. I was sure the indirect coil was leaking but after isolating it the problem was still there. Water feeder and relief had been replaced by an earlier plumber so I knew these were good. Turns out the bypass around the waterfeeder (used for fast-filling and purging) had a globe valve installed backwards. Whatever happened over time caused this globe valve to pretty much disintegrate on the inside and was leaking by. Yup turns out a 2 hour call could have been fixed in 15 mins...........sometimes I wish I did some more service work, although more times than not I am glad to stick with the commercial stuff

Expansion tank not big enough?

Is it a bladder tank? Pre-charged too high?

The valve between the tank & system is open - right?