Grant Combi Max oil-fired boiler overtemperature problem

[petes7457]

The above boiler randomly exhibits an over-temperature lock out.

Happens when in CH mode or HW delivery mode or just after periods (overnight) when it is topping up its hot water store.

Any suggestions as to what to suspect - over-temp sensor, thermostat sensor or pump? (The pump certainly sounds fine and the system seems as responsive as ever so I do not particularly suspect the pump).

Thanks in advance,

Pete

 

[oilhead]

Check that the heat store is venting properly. If you have an airlock in the heatstore, the thermostat may not be sensing quickly enough. ( Also happens on Worcester Heatslaves if AAV is blocked or turned off)

 

[Boilerman2]

Combi Max has an Electronic Stat fitted and the boiler is a Single tank design (no separate store) you will need to check the operating temperature of the Electronic stat with a digital thermometer is should stop the burner at about 75'c in heating mode and 85'c in Hot water mode, it could be that the microswitch assembly on the diverter valve has failed in the HW position and so is constantly running the boiler up to 85'c which is not too far of the overheat temperature pre set at 112'c