Error Light off

Safety first

- If you smell gas, leave the property immediately and call the gas emergency number. Do not operate electrical switches or the boiler. Call a Gas Safe engineer.

- Do not open the boiler case or attempt repairs to gas or high-voltage parts. Isolate mains power at the external switch before removing any covers for inspection and only if you are competent to do so.

- If in doubt, stop and call a qualified engineer.

Initial checks a homeowner can do

1. Check the controls: confirm the central heating programmer/timer is set to ON or that hot water is set to be available at the time you need it. If you have a smart thermostat or wireless controller, check the app/batteries and that it’s set to call for heat.

2. Check the room thermostat: turn it up well above room temperature to force a demand. If you have TRVs on radiators, open one fully for the test.

3. For hot water: open a hot tap fully and listen — the boiler should detect flow and try to fire. If nothing happens, note that down.

4. Check boiler power and display: ensure the boiler isolator switch is on and the display has power. Look for any other error codes on the display. If an EA or other flame-related code appears, do not repeatedly reset; call an engineer.

5. Check system pressure: the pressure gauge should normally be around 1–1.5 bar when cold. If pressure is very low (below about 0.7 bar) the boiler may not fire. If you are comfortable doing so, top up via the filling loop following the boiler manual, then re-check.

Simple diagnostic steps

1. Force a demand: set programmer to permanent CH or DHW ON and raise the room thermostat well above room temp. Open a hot tap fully for DHW test. Watch the boiler display and listen for pump/fan igniter noise.

2. Power cycle and reset: switch the boiler off at the isolator for 30 seconds and switch back on. If the boiler has a reset button you may press it once (check the manual for the correct reset procedure). If you see an EA error or any flame/fault codes, do not repeatedly reset — record the code and call an engineer.

3. Observe response: if the boiler now fires, monitor for normal operation. If it still shows "Light off" while you have the controls commanding heat/hot water, the boiler is not receiving the demand signal.

4. Check external controls and wiring (visual only): check the programmer/timer and thermostat wiring/connection points for obvious damage or loose plugs at the room thermostat or wireless receiver. Do not disconnect or work on live wiring unless competent. If you can safely isolate mains and are confident, you can check that the thermostat wires are connected to the correct call-for-heat terminals on the boiler; otherwise leave this to an engineer.

5. Bypass test (only if competent): briefly and safely short the thermostat call-for-heat terminals at the boiler to see if the boiler fires. If it does, the problem is upstream (thermostat, programmer, receiver). If it still does not fire, the problem is internal to the boiler (flow sensor, pump, PCB, diverter valve).

When to call a professional

- Call a Gas Safe registered engineer if: you are unsure at any point, the boiler still does not fire despite correct controls and the checks above, the boiler displays other fault codes (EA, E2, E9, etc.), there is a persistent low pressure issue you cannot resolve, you detect gas smells, or internal components (diverter valve, flow sensor, pump, PCB) are suspected.

- Tell the engineer the boiler model, the exact message shown ("Light off" / "No boiler demand") and the checks you have already carried out (programmer, thermostat, pressure, reset/power-cycle). This speeds diagnosis.

Notes and cautions

- Many causes are simple (controls set incorrectly, smart thermostat disconnected, low pressure). Those you can safely check yourself. Anything involving gas, internal electrical parts, replacing sensors, valves or the PCB must be done by a Gas Safe engineer.

- If you haven’t had a service in the last 12 months and the fault is intermittent or linked to performance, arrange a service to identify underlying issues and to prevent recurrence.