Set Appliance State:

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

Observation:

Allow the appliance to complete its self-check.
If fault code is displayed, reset appliance.
Does the display show the appliance flow temperature?
Note.
1. If the appliance fault code changes from the original to a different fault code, then CLICK HERE
2. If fault code is a recurring issue, then choose "appliance does not reset - fault code remains the same" to investigate possible causes.