Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4

Observation:

Visually inspect the 4 sensors on the appliance, flow / return, DHW and either heat exchanger or flue thermistor (refer to numbers on boiler / sensors).
Ensure they are correctly fitted to the pipes and flue collector as shown (they should be flush to the pipe or collector and firmly attached).
Are all sensors correctly attached?