Weil McLain Gold pressure valve issue (video)

Sounds like a bad expansion tank. System pressure should not rise above 12 to 18 psi if tank setup and operating properly.
Take pressure off the expansion tanks and check the psi.

post a couple pictures of the boiler and the expansion tank, please.

The PRV is from 1995. I don't see a tankless coil. That's a Series 1 WGO. Is there an indirect water heater? You can set cold pressure, then shut off the feed valve and wait a day to see if pressure rises. A relief valve not seating properly needs to be replaced.

If the problem is the PRV, have fun spinning it off. The knucklehead installers piped it so close to the boiler. Maybe Watts makes the same model and you can rebuild it.

Good air is coming out a valve, but you need to test with no pressure on boiler. Since there’s no way to isolate that expansion tank to take pressure off, I think you’ll have to drain down the system before checking psi on the tank.

once you’ve got it drained down, do yourself a favor and add a isolation valve with drain above the tank.

edit: once the boiler is drained down that will be an excellent time to replace the PRV

Is there a shut off before the fill valve?

This yellow handle looks to be a bypass around the prv for fast fill/ purge?

If there is another valve before the fill, turn it off, bleed down pressure. Then you can run the system.

Plenty of systems run with the fill valve turned off. All the time.

If pressure continues to rise and the expansion tank is not waterlogged, it may be the indirect leaking into the coil.

Provide pictures of indirect hot water tank and the valves you mentioned above. Try taking picture from a few feet further back.

did you replace the “GoodAir” that came out of the x-tank?

I see isolation valves (yellow handle 1/4 turn) on the three zones returns directly above the expansion tank.

I don’t see isolation valves on the supply side other than the zone valves.
Assuming those are normally closed you should be able to close the valves on the return lines and drain down boiler without drain draining rest of the house.

What’s your comfort level working on mechanical systems and plumbing?

the boiler looks ok. whoever replaced the water heater was a hack.

Checked expansion tank psi again and it was 30

that’s cause it’s reading the boiler pressure.
you only check the tank pressure when the boiler is at zero

can you provide pictures of new prv piping and TPRV?

1. ”For the additional isolation valve you suggested adding, this would be just for the expansion tank?”

Yes, for ease of maintenance.

2. “With the boiler drained and at zero the expansion tank reads 10psi.”

The expansion tank pressure should be set to 15psi for 2 story house; 12psi for 1 story.

3. Did you have the isolation valves for the indirect tank closed? (Valves above tank, shown closed in photos)

4. Did you replace the complete PRV? The body in the new looks old like the internals were swapped.

ok, since the HTP is isolated, the PRV must be the problem.
Drain down the boiler

Refill boiler and close supply valve to PRV when boiler PSI hit 15 psi.

if boiler pressure stabilizes at 15 psi, there is a problem with PRV body and you need to change entire valve.
(honestly, I’ve never heard of anybody swapping the internals of a PRV)

Good luck, should be a straightforward replacement.
PS: I think the HTP is fine.
🙏

there are rebuild kits for most PRVs. finding someone that knows how to order one can be harder.

with all that corrosion in the valve body you probably have something that isn't sealing.

does the pressure increase if you turn it off?