Error D.76

Safety precautions:

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

- Do not open the boiler casing or attempt gas or ignition-related repairs unless you are a Gas Safe registered engineer.

- Turn off electrical power to the boiler at the isolator switch before touching external wiring or pipework. Be careful with hot surfaces.

Initial checks a homeowner can do:

1. Confirm what the display shows: note D.76 and any egg-timer or status codes. Record a short video of the display while the heating is calling for heat, including room thermostat, programmer settings and any other symbols.

2. Check the room thermostat/programmer and confirm CH is calling for heat. If the thermostat is satisfied the boiler will not fire regardless of anti-cycle.

3. Check boiler pressure on the gauge. It should normally be around 1–2 bar. Low pressure can cause the system to behave oddly; top up only if you know how and the filling loop is accessible.

4. Look for a flashing egg-timer symbol. If present and the boiler is not providing heat, check condensate discharge for blockages (especially in cold weather) and ensure radiators/valves are open. Bleed a radiator if necessary to remove trapped air.

5. Note whether hot water operation is working. Anti-cycling applies to heating only; DHW should still run unless another fault is present.

Simple diagnostic and fixes you can try:

1. Reset the boiler correctly: use the boiler main switch or the reset button (hold ~10 seconds). The anti-cycle timer can be cleared by switching the appliance main switch off and on. Do not repeatedly power-cycle the unit as a long-term fix.

2. If the boiler repeatedly micro-fires (short on/off cycles) or attempts to restart immediately despite a D.76 reading, check that TRVs and radiator valves are open, and that the circulation pump is running (you should hear/feel it). If the pump is not running or is noisy, record this for the engineer.

3. If the boiler appears to be locked in anti-cycle (S.28/S.8 shown) beyond the expected time: note d.67 (remaining burner anti-cycle time) if you can access diagnostics, then try a single reset. If d.67 reads 0 but the boiler remains in anti-cycle, record that behavior and call an engineer.

4. Check for other symptoms that point to system issues: frequent egg-timer, low pressure, cold radiators despite demand, unusual noises, or the presence of other error codes. These suggest circulation, sensor or control issues rather than a routine anti-cycle delay.

When to call a professional and what to tell them:

- Call a Gas Safe registered engineer if the boiler remains in anti-cycle and will not fire when heating is clearly demanded, if anti-cycling appears excessive or recurring, if you suspect pump failure, blocked condensate you cannot clear, or if other error/fault codes appear.

- Tell the engineer: the displayed diagnostic D.76 (remaining anti-cycling time), what d.67 shows if you can read it, whether the egg-timer symbol is on or flashing, any status codes seen (S.7, S.8, S.28), recent behavior (micro-firing, stuck in anti-cycle after DHW/CH change), boiler pressure, and include your recorded video of the display and symptoms.

- The engineer will check system hydraulics and controls, pump operation, flow/return NTC sensors and wiring, the 3-port valve and settings (d.2, d.1, d.70 etc.), and the PCB/controls if necessary. Adjustment of anti-cycle parameters and any replacement of sensors or gas components must only be done by a qualified engineer.

Important notes:

- Do not attempt to change advanced diagnostic parameters (d.2, d.67, etc.) yourself unless you are competent and qualified; incorrect changes can affect safe operation.

- D.76 itself is informational; prolonged or inappropriate anti-cycling behavior is the issue to investigate. If in doubt, get a Gas Safe engineer to inspect and fix the system.