Pressure relief valve opening / pressure gauge continuously climbing Fault Fix undersized expansion vessel upgrade vessel size valve faulty or seat contaminated with sludge replace valve plate to plate heat exchanger faulty (fractured) replace plate exchanger filling loop faulty / passing pressure replace / cap off expansion vessel diaphragm has perished replace vessel expansion vessel has lost air charge re charge vessel Pump head failing (not at full capacity) replace pump head Boiler control thermostat faulty (causing overheat stat to trip) replace thermostat faulty gas valve (over gassing) check burner pressures…