Trying to see if I can figure out your problem here so please bear with me while I ask some questions that may apear to be silly but they need to be answered first to identify your problem.
1. You tell the thermostat to turn on heat and the heating unit lights up the main burners and after approximately one minute the fan switches on but does not run??
2. Does the pilot light remain alight when the heater fan fails to run – if it goes out then there is a control fault we need to identify.
Let me know the answeres to the above and we will wrok from there.
Selgas Services Ltd
Craftsman Gasfitters, Plumbers, Electrical Service Technicians