BoilerFaultCodesTechnical description
Demand lamp does not illuminate when central heating is set to ON / 230V at pin 4 of terminal X12
What causes this fault?
This fault occurs when the boiler receives an electrical signal from your thermostat telling it to provide heat, but the internal control board fails to acknowledge or process that command. The most common reason is a failure within the boiler's main brain or the internal wiring, meaning the system cannot bridge the gap between receiving your instruction and physically firing up the burner.
This fault often becomes apparent during the first cold spell of autumn when the heating system is switched on for the first time after being dormant all summer.
Engineer required
This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.