Greenstar Heatslave Oil Boiler Overheating and Pump Running 24/7

[Johntheo5]

I can't actually put the CH on "normally" ie turning the external thermostat up, as firstly I'd have to turn the boiler on at the spur and secondly the boiler will always heat the water tank first but this is heated so much it trips the high level stat. Yet, it must only know the tank needs heating from the tank thermostat data.

If I'm reading the electrical schematic correctly then it should be possible to put the CH on normally without the boiler heating the heatslave (DHW) tank first as long as the DHW is switched off at the programmer as the DHW Thermostat Live is fed through the DHW programmer. This also seems the logical way of operation. It also then maybe looks that if a HW tap is opened (DHW still programmed Off) that only lukewarm then cold DHW is available, the boiler should still not fire?.

 

[scottwhittaker]

The programmer on the boiler was removed before we moved in. I presumed it was a simple timer/programmer that the room stat replaced. We have a nest smart thermostat but that only works the heating on off and from what I've read online it's not possible to have the boiler not heat the heatslave tank by default.

Even if we call for heat the diverter valve will stay on water until the heatslave tank is up to temp.

 

[Johntheo5]

Well, if turning the DHW stat down switched off the boiler before your problem and even though it's clicking when you do so, it's possible that the stat has failed on, if you remove one of the wires from the stats terminals then that should tell you something?. OR when when the stat is apparently off check for NO 230V on one of it's terminals with power on.