I am having problems with a worcester 350 rsf combi which works perfectly on heating mode also on hot water (when also on heating mode ) but when on a water demand when the heating is off it will supply any amounts of hot water at good temperature and flow but after demand finishes burner shuts down and the fan starts up as it should to cool the heat exchanger but within a few seconds the boiler locks out . Both water sensors have been replaced and a new o/heat stat fitted but the problem persists. Funny thing is if you immediately push in the o/heat stat reset button it resets without problem ie no resistance felt . British gas engineer at a loss as to what is wrong . Any ideas appreciated!
