Water pressure problem - WSHP closed loop with boilers and cooling tower

[adwood75]

We recently drained the system to repair a leak. After refilling the system, the boilers started leaking from the pop off valves. The pressure at the boilers is 45 psi and sometimes goes up to 65 psi when they are heating causing the pop off to drip. The part that I don't understand is that I have 12 psi on several parts of the loop. I read 45 psi at both boilers, at the cooling tower, and outlet of the pump. I read 12 psi at all of the WSHP units, and on the return side of the pump. I believe all the air is out of the system and the expansion tank is okay. I figured the problem was in the 3-way mixing valve but after disassembling it and checking everything, it seems to work properly. Can anyone tell me what I'm missing? I don't have a lot of experience on this type of system. Thanks!

[lwarren]

Sounds like an expansion tank issue.

[terpfan_]

valve off make up and bypass and see if you still have problem. B&G says to close outlet of prv when system is filled. could it also be just a leaking relief? not much else going to cause this problem besides what has already been stated.

[atmosphere]

The expansion tank is okay..... meaning??

[adwood75]

I drained the expansion tank and checked the pressure. It was 12 psi and no water was on the air side so I think the bladder is good.

[atmosphere]

Are the boilers tempering this loop directly, or do they do it thru a heat exchanger?

[adwood75]

Directly

[atmosphere]

Are your boilers on the same level as your pumps, are are they lower? Your loop psi may be too high.

[terpfan_]

A few things to check. Is expansion tank supposed to be set at 12 psi (normally sent from factory at 12 psi). Is the Bypass valve and prv inlet shut after filling system. Boilers are not over firing? I also recently had the bypass valve on system leak by over period of days to build system pressure.

[atmosphere]

Where your boiler is located in reference to your pumps is important to know. Also if you have a multi storey bldg. where are the pumps.

[james mo]

sounds like your pump is pumping to the boilers and the compression tank is piped to the pump return. 12psig fill pressure + pump pressure is what you are seeing at the boiler. If you pump away from the boilers, then they will be at fill pressure.

[fitzyfitta]

What is your "pop off" relief valve rated for? Did the system run last winter without the relief leaking? If the exspansion tank is set to the correct pressure, I'd be checking the make up water valve. I've seen them leak bye or not set correctly causing the pressure to build.

[atmosphere]

Where your boilers are located in reference to your pump package will make a difference.
Think about column weight in your risers.

Ground control to Major Atwood...