So i fitted new combi cylinder last year and replaced ballcock in tiny cold water storage tank at same time. Bank holiday weekend went over and changed both ballcocks both tanks share 1 overflow. Both shut off happy days. Phone call day to say water is ****ing out of overflow... Been over tested both ballCocks all seem fine bent them a tiny bit more just to make sure they shut off hard. Just had another call to say dripping again outside. Also noticed today top tank in combi was warm water to touch... think this is just conduction or thermostat failed? Any ideas?