Error Slow flash ( mostly on flashes off)

Safety first:

1) If you smell gas or suspect a gas leak: evacuate the property, do not operate electrical switches, and call the gas emergency immediately.

2) If you see soot, flames, or the boiler keeps running hot and will not shut down, turn off the boiler and isolate the mains electrics and gas supply if you can do so safely, then call a Gas Safe engineer.

3) Never remove the boiler cover or work on gas/electrical parts unless you are a Gas Safe qualified engineer.

Initial homeowner checks (safe, external, low-skill):

1) Note the exact flashing pattern and any displayed codes. If your model has a spanner/return button, press it to view any stored cause code and record it for the engineer.

2) Try a basic reset: press and hold the reset or ✔ button for about 8 seconds (or follow your manual). If the fault does not reoccur, monitor the boiler closely. One reset is acceptable; repeated lockouts indicate a persistent problem.

3) Inspect the flue terminal outside: look for leaves, nests, snow, or debris blocking the terminal. Do not insert objects into the flue; if you can safely remove superficial debris, do so. If you cannot reach or the terminal is obstructed internally, stop and call an engineer.

4) Check the condensate pipe (if visible): in freezing weather the condensate can ice up and restrict operation. Carefully pour warm (not boiling) water around the exposed condensate pipe to thaw it if you suspect freezing.

5) Check system pressure on the boiler gauge: combi boilers typically sit around 1–1.5 bar when cold. Very low pressure may indicate a leak or circulation problems. Do not over-pressurise the system.

6) Check radiators and heating circulation: with heating on, feel radiators for cold spots (especially at the bottom) which can indicate sludge or poor circulation. Listen for the pump running (a low hum) and for unusual noises.

If the fault persists — safe diagnostic steps to communicate to the engineer:

1) Record behaviour: when the boiler locks out (time, whether it was on DHW or CH, whether you were running multiple outlets), any noises, and the exact flash pattern/cause code. This speeds diagnosis.

2) Do not attempt to bypass safety thermostats, sensors, or the lockout. These are there to prevent damage and danger.

3) If you can safely switch the boiler off and leave it off, do so until a Gas Safe engineer arrives. Switching the boiler on and off repeatedly is not recommended.

Likely professional checks and fixes (for the engineer):

- Inspect and test the flue and flue gas temperature sensor; check for blockages or corrosion and that the flue path and termination are correct.

- Test the safety temperature limiter and flow/flue sensors for open/short or out-of-range readings and replace sensors if faulty.

- Check combustion fan operation and air supply; repair/replace fan or control module if required.

- Test circulation components: pump operation, diverter valve function, motorised valves, and check for sludge/scale in the heat exchanger causing restricted flow. Powerflush or descale/replace heat exchanger if required.

- Check PCB and control modules if intermittent/incorrect fault reporting is suspected.

When to call a professional immediately:

- Repeated lockouts after reset.

- Any sign of flue damage, soot, burning smell, or the boiler running hot without control.

- No gas flame, gas smell, or suspected leak.

- If you cannot safely access or clear an external flue obstruction.

Information to give the engineer when you call:

- Exact fault indication (slow flash mostly on), any cause code from the spanner menu, recent behaviour (when it happened), whether reset cleared it temporarily, visual checks you carried out (flue, condensate, pressure), and whether you smell gas.

Final note: this error is a safety lockout. Small external fixes (clearing visible flue debris, thawing condensate) are safe to attempt, but internal diagnosis and repairs must be done by a Gas Safe registered heating engineer. Arrange a prompt service call rather than continuing to reset and run the boiler.