Error D.67

Safety first

1) If you smell gas, turn off the gas at the supply and call the gas emergency number immediately. Do not attempt anything further.

2) If the boiler is displaying other fault codes, repeated lockouts, or is completely dead, call a Gas Safe engineer rather than attempting repairs.

3) Before any checks, switch the boiler to standby and allow it to cool if you need to touch pipework.

Initial homeowner checks (safe, simple)

1) Confirm the egg-timer (radiator) symbol is being shown and note the D.67 value if you can read diagnostics. This number is how many minutes remain before the controller will allow re-firing.

2) Check system water pressure on the gauge; it should normally be about 1.0–2.0 bar. If pressure is low, follow your boiler manual to top up the system. Low pressure can cause problems and should be corrected.

3) Bleed radiators to remove trapped air; air can reduce flow and increase temperature swings at the boiler.

4) Make sure thermostatic radiator valves (TRVs) or any zone valves are open so the system can circulate. Closed valves can starve the boiler of flow.

5) Check that the circulating pump is running when there is a heat demand. With the boiler calling for heat, carefully feel the pipes either side of the pump (after allowing to cool a little if recently fired) or listen for pump noise. If the pump does not run, the boiler may overheat and enter anti-cycle or other protective modes.

6) Check condensate pipe for blockages only if you have freezing weather and the condensate is routed outside; a blocked condensate causes other faults but is easy to spot if water is frozen or blocked.

Diagnostic steps to gather useful information (for you and the engineer)

1) Record a short video showing the boiler display and pipe temperatures if possible while the issue is happening. Include the D.67 readout, any status symbols (egg-timer/radiator, burner, gas valve), and timing of messages. Note outside temperature and heating curve setting on any weather compensator (VRC430). Engineers find this very helpful.

2) Note the target flow temperature from the controller/room stat/heat curve when the issue occurs. The anti-cycle effective time is derived from that target and the D.02 maximum setting.

3) If you can access boiler diagnostics safely, note D.02 (max anti-cycle), D.01 (pump overrun), and D.70 (bypass position) values. Do not change these yourself unless you are trained.

Practical troubleshooting and temporary fixes you can try

1) Improve hydraulic flow: open more TRVs, fully open the lockshield valves, and ensure no zone valves are stuck closed. This often reduces rapid overshoot of flow temperature.

2) Bleed radiators and ensure no large airlocks exist. Air reduces system flow and can cause the boiler to heat the flow quickly and then cut out.

3) Increase pump speed setting (if you have a multi-speed pump and can change it safely at the pump head) by one step to improve flow through the heat exchanger. If you are unsure, call an engineer.

4) On weather compensators (VRC430) check if Pump Delay Time is set (some users reported pump delay causing short firing patterns). If Pump Delay is set to a long time, it can change how the boiler behaves; changing this requires knowledge of the system and is best done by an engineer.

5) Temporary workaround: a full mains switch off/on resets the anti-cycle timer (manual reset cancels it). This is only a temporary measure and not a fix for the underlying issue.

When to call a professional (and what to ask them to check)

1) Call a Gas Safe registered engineer if the problem persists after basic checks, if you are not confident performing the above checks, or if the boiler shows other fault codes. Mention D.67 and provide the video/notes you collected.

2) Ask the engineer to investigate flow/return temperatures, delta-T behaviour, pump sizing and speed, automatic bypass valve setting, proper pump overrun/delay settings on any controller (VRC430), and whether Minimum Flow Temperature or heating curve needs adjusting. These items are commonly implicated in micro-firing and anti-cycling loops.

3) Do not ask anyone who is not Gas Safe registered to alter gas or sealed-system components, or to reconfigure advanced D-parameter settings unless they are qualified. Parameters like D.02 (max anti-cycle time) can be changed to influence behaviour but should only be done by a competent engineer after diagnosing the hydraulic cause.

Final advice

1) D.67 itself is an informational/operational value showing remaining anti-cycle time; it is rarely a direct component failure. The root cause is usually hydraulic (insufficient flow, bypass, pump, or radiator configuration) or control settings causing the boiler to reach target temperature too quickly and cut out.

2) Collect evidence (video, temperatures, times, settings) and give that to your Gas Safe engineer; it will speed diagnosis. If heating loss is significant or recurring, do not delay getting a professional inspection.