ideal Classic 18 SE FF electrics?

My central heating system is fired by an Ideal Classic 18SE FFboiler.
The system has an intermittent fault. It is programmed to come on twice a day, but on shutdown the circulating water pump sometimes continues to run, also the boiler will fire up whilst the system is switched off. A plumber informed me that the hot water motorised zone valve (Drayton ZA5) was faulty (sticking). This valve actuator was replaced with a new one, but the problem persists. Has anyone had a similar problem And resolved it ?

Allan
December 2009