What's causing high pressure in HW Boiler

Kyle Kubs

Ok, I need to defer to the real pro's here... Inspected a house last month. Older oil fired weil HW boiler. Pressure cold was around 20psi. A bit high, especially for a two story on a slab, 12 would have been fine, but ok... Crank er up and the pressure starts climbing right away. I'm watching and it hits 30... 31...32... Still no discharge from the PRV. I shut it down and check the expansion tank - the first few inches near the tapping is good and hot but the rest is cold so I assume the bladder isn't ruptured and the tank isn't water logged. So my question is, barring a bad expansion tank, what else would cause a high pressure condition like that. I did turn off the fill valve to isolate a pressure reducer that was being somehow affected by the heat even though that is unlikely. Of course I recommended the client bring in a hydronics pro for an evaluation but they never get back to me to let me know what it was...

Weezbo

You Told us the water pressure is 20 psi.

Theres the answer.reduce the start up pressure ,reduce the temperature, not everyone uses a 30 psi pop off...the domestic coil has a leak that gets particulairily bad with heat,the gage is lying to you,the high limit is fried and the gage is lying there by pumping X psi cold water to<Temps than normal.. theres a few ideas on what may be happening.

tim smith

rising pressure

It would have to be either a blocked line to expansion tank or a bad or depressurized expansion tank. Also check setting on prv, if 30 and gauge is accurate, replace it. Also agree that the pressure only needs to be around 14-15psi. Good luck, PS it could be what Weezbo say's also but I would be surprised.