I have an NV heater and the main fan is turning on & off on its own when the burner is firing

Fan command module

In heating mode, the main fan on the NV heater model is controlled by the fan command module.  This is a small black box with a small adjustment screw in the corner and found on the heater's control panel.  If the fan is not operating as it should, the fan command module is faulty and needs replacing.  To test this further, run the heater in summer (fan only) mode.  If the fan performs as it should in this mode, the fan command module is faulty.  Nb. in summer mode, the fan command module is bypassed.

The replacement part number is 142403605/KIT and is available by contacting our spares team (spares@powrmatic.co.uk)