Error D.65

Safety precautions:

1) If you smell gas (rotten egg/sulphur smell), do not operate any electrical switches, open windows and doors, leave the building and call the National Gas Emergency number immediately. Do not attempt repairs.

2) If you are unsure or uncomfortable at any point, stop and call a Gas Safe engineer. Working on boiler internals or gas components is hazardous.

Initial homeowner checks you can safely do:

1) Record the exact error code (D.65) and any other codes or behaviour (e.g. flames seen then lost, repeated lockouts, noise). Note when it happens (heating or hot water demand, after reset, after frost, etc.).

2) Check other gas appliances to confirm gas supply to the property. If other appliances are out too, contact your gas supplier.

3) Check the gas meter isolation (service) valve is open (if you know where it is and can safely confirm).

4) Check the boiler’s power supply and display; ensure the boiler has mains power and the programmer/thermostat is calling for heat.

5) Check the boiler pressure gauge — it should normally read about 1.0–1.5 bar when cold. If pressure is very low, top up using the filling loop following the boiler manual, then try a single reset.

6) Try a single reset of the boiler: press and hold the reset button as the manual specifies (commonly up to 10 seconds). Only attempt one reset; repeated resets can flood the appliance with gas and are not advised.

7) Visually check outside the property for obvious flue blockage (nests, leaves) at the flue terminal. If you see a blockage you can safely remove it if obvious and external; otherwise call an engineer.

8) In winter check the condensate pipe (external plastic pipe from boiler) for freezing — thaw with warm (not boiling) water or run warm tap water over it. A frozen condensate pipe can stop ignition and cause lockout.

Specific diagnostic steps and what a Gas Safe engineer will do (do not attempt these yourself unless you are qualified):

1) If the basic checks above don’t clear the fault, contact a Gas Safe engineer and report D.65 and the checks you completed.

2) The engineer will check gas supply pressure at the appliance and the integrity of the gas valve and its wiring. Low inlet pressure, a faulty gas valve or incorrect valve regulation will prevent ignition.

3) The engineer will inspect ignition components: ignition electrode, electrode lead, spark generator/ignition transformer and connections. They will test electrode gap and condition and replace parts if corroded or faulty.

4) They will test flame detection circuits (ionisation or flame sensing) and the PCB if required. Intermittent wiring, poor connectors or a PCB fault can cause the boiler to time out on ignition.

5) They will check the flue and for flue gas recirculation or blockages, clean and test the flue gas temperature limiter (STB) if fitted, inspect condensate discharge and clean or replace condensate trap if blocked.

6) They will inspect and test other sensors and safety interlocks (flow/return sensors, pump operation, earthing) because related faults can prevent normal ignition or create unsafe conditions.

When to call a professional:

- If the fault remains after the basic homeowner checks and a single reset.

- Immediately if you detect a gas smell or any leak, or if you are unsure about any inspection.

- If the error returns repeatedly: this indicates a component is failing and needs proper diagnostic tests and replacement by a Gas Safe engineer.

Additional advice for the engineer visit:

- Provide the engineer with the exact error code (D.65), any secondary codes, how often it happens and what checks you have already done. That speeds diagnosis.

- Do not attempt to alter or replace ignition electrodes, gas valves, wiring or PCBs yourself. Those tasks require a qualified Gas Safe engineer.

Summary: D.65 is an ignition timeout and a safety lockout. Perform the safe, simple checks listed above (gas supply, pressure, reset, flue/condensate visible checks). If the fault persists, contact a Gas Safe registered engineer to diagnose and repair the ignition, gas supply, electrode, valve, sensor or electronics faults that commonly cause this code.