Boiler does not respond to room thermostat or programmer, but power light is on.

Safety: Isolate power before accessing any wiring terminals.

User checks:

• Replace batteries in wireless or battery-powered thermostats.
• Confirm the programmer is set to ON and not in holiday or OFF mode.
• Increase the thermostat setting above current room temperature.

Engineer checks:

• Verify correct wiring of the thermostat and programmer to the EHC boiler control terminals.
• Test continuity of control cables and repair any breaks.
• Temporarily link the boiler’s call-for-heat terminals; if the boiler fires, replace the faulty external control.

After restoring control signals, test both heating and hot water schedules for correct operation.