Boiler electr. system fault
Remedy
Unexpected feedback from the modulating/current controlled gas valve.
Check the voltage to the gas valve.
Check the continuity of harness and replace if required.
Check the resistance on the gas valve coils pins 1–2 (SIT; 55...66.8...85 / Resideo; 110...114.5...120 ).
The gas valve or the appliance electronics (control unit) may have a fault.