Climbing system PSI when boiler is off

Jimbo_5

I have a TT 110, with indirect tank, installed about 12 years ago. It's been running fine. Today I noticed the PSI in the system that normally sits at 13PSI when off/cold was reading just above 15 PSI. It was a warm day out, upper 60s, so other than making hot water the system has been off. The makeup water is shut off. Any ideas why the pressure would suddenly rise? Thanks.

A few years ago the expansion tank crapped out on it though. No idea why.

Solid_Fuel_Man

Valve out your indirect tank and see what happens. The coil may have a pinhole allowing domestic water into the lower pressure boiler coil. 

Jimbo_5

Thanks, I tried that. I don't think it would continue to sit steady at 15 psi if it were leaking through though. It's driving me crazy. It's still warm out, 50s, so I'll wait till tonight when it drops into the 20s and the boiler fires up and see what the pressure does. It does rise a pound or two when the water tank calls for heat.

Months ago, the pressure dropped to 0 one day for no obvious reason. I opened the makeup water valve for a few seconds ....and all of a sudden it was back to 13 psi. I'm using a good gauge, not depending on the tiny one mounted on the boiler so I don't think that is an issue. Weirdly possessed....

Solid_Fuel_Man

Your expansion tank is likely at 12 psi and thr diaphram was at the top. With just a cup of water to bring pressure back up to normal operating pressure of 13 psi.

I'd say aa long as it stays at 13 to 15 its completely fine. If anything open the fill and have it at 14 or 15 cold. Then there is a bit of cushion with your makeup shut off. That's how I operate my own system. I leave the makeup on for customers.