Pressure relief valve dribble

_big_

Hydronic floor heat system with DHW sidearm. About 20 years old.

In the 20 years, I've replaced the pressure relief valve in the primary loop twice, I'm on my third valve and its leaking again. It had a pretty good stream, but I diddled with it and now its just dripping.

Last time I replaced it, I got smart and installed a union to make it easier the next time. But... I don't think I should have to replace this thing... ever.

Any advice from the pros?

pecmsg

What's the pressure in the system?

_big_

Good question. About 28 psi. Which I think is quite reasonable.

pecmsg

The relief is set for 30#'s. Sounds like the relief is doing it's job, Why is the pressure that high?

_big_

>> Why is the pressure that high?

Dunno?? That's the way the original plumber set it up.

_big_

Went here: https://www.watts.com/products/plumbing-flow-control-solutions/relief-valves/asme-safety-valves/335/335m2-030-34

Maximum Working Pressure-PSI 20

I think that answers my question. Thanks.

EBEBRATT-Ed

@_big_ you should only be running 15 psi cold unless your in a multiple story building over 2 floors.

If you have pressure issues it is usually the water MU prv or the expansion tank.

_big_

I've got it adjusted down to about 16 psi, warm. Fiddled with the pressure relief valve. Its much better now, but it still drips a little.

Should I expect the pressure relief valve to be absolutely dry under proper/normal conditions?

EdTheHeaterMan

_big_ said:

I've got it adjusted down to about 16 psi, warm. Fiddled with the pressure relief valve. Its much better now, but it still drips a little.

Should I expect the pressure relief valve to be absolutely dry under proper/normal conditions?

Yes. But since it has been passing water over the valve surface for some time, there may be some debris or erosion on the valve mating surface that is preventing complete closure.

When water is heated, it expands. The expansion tank is supposed to accept that "EXTRA" volume of water and put that extra water back into the system when the water cools off. By operating at 28 PSI, there is very little margin for the water expansion before the pressure reaches 30# where the relief valve is supposed to do its job and release that pressure.

Now that you have the operating pressure at a reasonable level, you can replace the relief valve and expect it to last much longer.

Intplm.

At your set working pressure of 28 psi your 30 psi relief valve tolerances are being tickled to that trickle.
(odd sentence) but that is much to close to the set point of the relief valve.
Also, there is very good chance that the pressure gauge could be reading just a bit off and the relief valve could be a tad off too.
Lower your pressure to the systems recommended pressure and and if the relief valve is shot, replace it with a higher quality relief valve.

_big_

Following an extended detour through an intermittent pilot problem, I finally got back to this.

Figured out the expansion tank was bad. You can figure this out by tapping on the side of the tank. You should be able to hear where the water line is. Replacing the expansion tank was somewhat challenging because it hangs from the air eliminator and there was not nearly enough room for a wrench. Had to find a thinner wrench.

Pressure still too high. Decided the make up water valve was shot. Valve had an amazing amount of gunk in it:

I live in Northern Colorado. Our water is basically snowmelt and quite good. Surprised by the gunk.

Was forced to loosen a fitting on the backflow preventer to replace the makeup water valve. Didn't want to do this. Sure enough it leaked when retightened. The joint on the backflow preventer is some kind of flat flanged union. There was no way I was going to clean up the flanges, plus I needed a new washer that I don't know where to get. Decided to replace the backflow preventer as well. Its probably as gunked as the makeup water valve, and a non functioning backflow preventer is a health hazard.

So finally, it took an expansion tank, makeup water valve and a backflow preventer and I finally have proper pressure in my heating system and no dribbling from the pressure relief valve.

hot_rod

That looks like an iron body fill valve? Brass versions are less prone to gunking up from within.

_big_

Huh. Fill valve is brown in color, just assumed it was brass. A bit of filing shows the brown to be paint over a metal that appears to be some sort of iron.

Since I'm an amateur, I intentionally replaced the existing valve with an identical unit. Not smart enough to change to a different part number.

pedmec

Keep an eye on the pressure. Doubt your plumber would set it that high. You might have a bad sidearm dhw and it could be causing the increase in pressure in the boiler. Unless he really knows nothing about heat which i doubt.