Error 4 flashes, 5 second gap, 2 long flashes

Safety precautions:

1. If the boiler is displaying this fault, stop calling for heating or hot water from the programmer/room thermostat and turn the boiler off at the on/off switch or the mains isolator. Do not attempt internal electrical or gas repairs. Allow the appliance to cool before touching pipework — flow and return pipes may be very hot.

2. Do not remove the boiler casing or attempt to access gas / combustion components. Any work inside the boiler must be done by a Gas Safe registered engineer.

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

Initial homeowner checks (safe, non-invasive):

1. Attempt one controlled reset: follow the manual for your model — either press and hold the reset button for about 3 seconds or turn the control knob to the reset position and hold for 3 seconds. Turn the boiler back on and observe. Do not keep resetting repeatedly; only try once or twice to prevent masking a real fault.

2. Check the system pressure on the boiler gauge. Normal cold system pressure is usually around 1–1.5 bar (check your manual). If the pressure is very low (<0.5 bar) or very high, note that and report to the engineer. Do not repressurise unless you are familiar with the boiler filling loop procedure and your manual instructs you how.

3. Check that heating system controls, thermostats, timers and TRVs are set correctly and have not been accidentally turned to maximum or set to an abnormal program.

4. Listen for pump noise: when the boiler tries to run you should hear the pump. If you hear nothing or a loud grinding/struggling noise this can indicate a seized or failing pump or airlock.

5. Check radiators to see whether they are hot or cold. If the flow pipe from the boiler is hot but radiators are cold it suggests a circulation issue (pump, closed valve, valve stuck closed, or airlock).

6. Bleed one or two radiators (starting with the highest ones in the house) if you suspect air in the system, but only if you are comfortable doing so and have a container and cloth. Beware hot water.

7. Confirm any external isolation valves to the boiler or on the heating return/flow pipework are open (if accessible and clearly marked). Do not force valves.

Specific diagnostic and next steps to tell an engineer / prepare for visit:

1. If the fault does not clear after a single reset or returns immediately, turn the boiler off and leave it off. Note the exact flash pattern and any other lights or displayed text, the date/time the fault started and any recent events (power cut, recent servicing, freezing temperatures, noisy pump or blocked pipework).

2. Do not keep using the boiler. Repeated firing with a safety over-temperature condition can damage the heat exchanger and components.

3. When you contact a Gas Safe engineer, describe: the 4 quick flashes, 5 second gap, then 2 long flashes message (safety temperature too high), what you have checked (pressure, reset, radiators, pump noise), and whether the boiler has been serviced recently.

What the engineer will typically check (do not attempt yourself):

1. Measure actual flow and return temperatures and compare to expected values to confirm real overheating or false reading.

2. Inspect and test the safety/sensor NTCs (flow/safety sensor and wiring) and connectors for faults, short or open circuits.

3. Check circulation: pump operation, motor current, pump speed settings, jammed impeller or airlocks, and verify motor and pump head performance.

4. Check the three-way/diverter valve (on combi units) for correct operation and any mechanical seizure.

5. Inspect heat exchanger and condensate paths for blockages, scale or restrictions that could cause poor heat transfer and rapid temperature rise.

6. Check control board error logs and PCB operation; replace safety/sensor or control components if proven faulty.

7. Test and, if necessary, replace the high limit thermostat or safety limiter if it has tripped or failed.

Final notes and warnings:

- This error can be caused by either an actual overheat (circulation or heat-exchanger issue) or a faulty sensor/wiring. Because it involves safety temperature controls and potential gas/combustion components, professional diagnosis and repair by a Gas Safe registered engineer is required if the simple homeowner checks and a single reset do not clear it.

- Do not open the boiler casing, attempt to replace sensors, or perform gas/electrical repairs yourself. Call a qualified engineer and provide them with the exact fault flash pattern and the checks you have already completed.