Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
DHW circuit of appliance drained and discharged

Observation:

Remove and inspect the DHW filter.
Note: Located in the cold water inlet immediately after the cold water service valve, access can be gained by removing the threaded bush when the blanking cap has been removed. Care should be taken as some water may remain in the appliance although it has been discharged and drained.