boiler operation

[amishron]

I have a residential boiler that keeps building more than the 30psi. that the relief valve is set at. I know that it is developing more pressure than it should, but don't know why. Need to know what is going on with the boiler & what to do.

[beso]

Sounds like a problem with the thremostat.

[buildersmate]

These things are usually set to 1 bar, which is about 14psi. The pressure relief valve is then set to 3 bar, or around 40psi. If the pressure goes above this, the excess water comes out of the relief and vents, usually to the outside where it drips.
First things first. Are you sure that the cold water filling loop is not allowing a little more water into the sealed system?

[webdude]

Maybe the expansion vessel is faulty, is the outside of the casing hot to the touch?

[gucciman]

nine times out of ten this is caused by the expansion vessel being flat of air, best call out an engineer to re-pressurise it.
check that the filling loop is definately closed first as buildersmate suggests.