I have a client with the above boiler who complains that it keeps locking in hot water mode. Boiler resets ok. This is an intermittant (groan) fault and every time I visit it works fine despite my best efforts to make it overheat. Diverter valve was changed a couple of years ago. Am I right in thinking that when the thermistors play up they cause the boiler to cut out rather than overheat? Anybody else had this as an intermittant problem?