gas boiler wont fire up.water pressure at 3.5 bar .when switched on pressure goes to 4bar and shuts down.how do i get water pressure down to 1.5 bar.make of boiler is ariston microcombi23/27 mffi type c
by letting water out of the bleed valve on any of the radiators. the real isssue is why pressure is rising query expansion vessel. make sure the water inlet pipe to top up pressure is not leaking.