water loss from external overflow pipe on ariston micro combi 23 when heating is switched off water leaks until pressure drops to zero,if you top boiler up using flexi pipe it will run fine until switch off again then leak until pressure drops to zero.have tried replacing thermostat (overheat)any sggestions most appreciated

bill d, November 2009

the PRV need changing and the expansion vessel needs
to be checked at the same time

b, November 2009