DIY Doctor UK DIY Forums

Hello All,

I have a traditional vented system, Honeywell Sundial setup with Glowworm 50FF boiler.
CH works fine, Diverter valve appears to work ok (B is hot when HW on, A is hot when heating on). When call for HW, pump fires, boiler lights then goes out after a few minutes. Pump continues to run.

Cylinder thermostat measures 240v and seems to trigger a simple on/off when I vary the temperature. When "at heat" the pump stops. When calling for heat, the pump restarts, so does the boiler.

Boiler registers no fault on LED panel. CH works fine and boiler doesnt cutout.

Thank you in advance if you have any ideas or need more info.
Justin

I know this may seem daft, but is the boiler temperature below the DHW temperature by any chance?

The tank thermostat turns on boiler when DHW is required and when DHW plus CH is required, so if you are getting it working when both are called for, then that is OK.

But the boiler is designed with two temperature sensors, one out going water, and one return water, it out going water is too hot boiler turns off, and if return water too hot boiler turns down, or starts to cycle.