Hi, I've had this back boiler installed and working for 5-6 years now without any problems (Pumped CH with Gravity HW incl.2 way Motorized valve and Cyl Stat) , the boiler is serviced annually (due april).
A couple of days ago at around 11.00pm (after being "on" all day) the system began banging and clattering due to over heating - Although the programmer (Horstmann C27) was set as usual on the 24H setting neither the HW or CH were asking for heat but the boiler was running! I switched the system off, let it cool down then re-started it.
Everything was fine until last night at around 9.00pm when the same thing happened. This time I was in the same room as the B/boiler and heard a "boinging" sound on a couple of occasions as the boiler fired up ( sounded like a relay was not operating correctly) I shut down the system before the water overheated, let it cool down and re-started - again everything is ok today.
My initial thoughts are that it could be either a relay on the PCB that is causing the problem or the thermostat - or both?
Any Ideas??
Kev