Set Appliance State:

CH Demand
Isolate Mains Power to appliance as per TOPs P4
Release the front facia by gently prising up the retaining
latches at the top of the facia
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Test 1:
Turn 'service potentiometer' fully clockwise to put boiler to MAX Output.
Measure the combustion readings.
Readings should be within the parameters outlined in ADAPT / TOPS.
Test 2:
Turn 'service potentiometer' fully anti-clockwise, hold it in this position for about 5 seconds before rotating the service potentiometer clockwise to the mid-point or 3 o'clock position. Fan speed will reduce and boiler will now be running at MINIMUM output.
Measure the combustion readings.
Readings should be within the parameters outlined in ADAPT / TOPS.