Set Appliance State:

Mains Power Off
Ensure NO demands are present
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Reset appliance (press reset button for 2 seconds and release).
Apply a demand, allow the boiler to run, does the fault code E33 reoccur?
Note:
1. It may take up to 25 seconds after a demand for fault code E33 to occur.
2. If after applying a demand the fault code changes to a different fault code, then CLICK HERE.
3. Reset is confirmed by the display returning to show ON when NO demands are present.