My gas boiler supplies both heating and hot water independently. Recently the pump only switches off if the hot water side is switched off (either on the timer or by manual over-ride) before the heating side. Switch off the heating before the hotwater and the pump keeps running (and the pump noise increases) and the gas burner may also reignite (if the thermostats demand). Both valve actuators appear to operate normally. I have replaced the timer/control unit with a new one but the unusual behaviour persists. Any ideas anyone?