Grant combi CHP not running

[IrishTaff]

Grant combi boiler, Light on CHP not on and no electrical supply to pump, programmer switch set to constant. DHW pump light on and running but programmer switch is off. Check one way valve on CHP seems to be free and working.

 

[exedon2]

Which model Grant combi there are several.
CH will not work if there is a DHW demand which DHW pump running suggest there is .
If you have a multimeter and are competent to use it check if there is a live feed back from flow switch.