Error Overheat lockout

Safety first:

- If you smell gas, do not touch the boiler. Open windows, leave the property and call the gas emergency number immediately.

- If there is a visible water leak that risks electrical contacts, turn the boiler off at the fused spur and isolate the water supply if safe to do so. Call an engineer.

- Never remove the boiler cover, disconnect gas pipework, or attempt internal electrical repairs unless you are a qualified Gas Safe engineer.

Initial checks you can safely do:

1) Note the exact fault message and the time it happened. This helps the engineer diagnose later.

2) Check the system pressure gauge on the boiler. For combi boilers aim for around 1.0–1.5 bar when cold (follow the pressure figure in your user manual). If the needle is below about 1.0 bar, the system may not be circulating properly.

3) Open radiator bleed valves (start at the highest floor) to remove air pockets. Re-check pressure and top up after bleeding.

4) Check that all radiator valves and the boiler heating flow and return isolation valves are fully open. Make sure the boiler mode and room thermostat (or programmer) are calling for heating when you test.

5) Listen and feel: with the boiler calling for heat, carefully feel the flow and return pipes (avoid burns). If the flow pipe is hot but the return stays cold, circulation may be poor or the pump may be blocked/seized.

Reset procedure:

- Reset the boiler using the reset button on the control panel or turn the boiler off at the fused spur for about 30 seconds and turn it back on. If the fault clears and the boiler runs normally, monitor pressure and operation over the next 24–48 hours.

If the fault continues after the above:

1) Re-pressurise the system using the filling loop to around 1.2–1.5 bar (follow your manual). If you cannot get pressure up or it won’t hold, there may be a leak or a faulty component—stop and call an engineer.

2) Check external condensate pipe (in freezing weather it can freeze) and clear any obvious external blockage if safe to do so. Do not dismantle internal condensate connections yourself.

3) If you still see the overheat lockout, or if you hear unusual noises (rumbling, banging), or the pump appears not to run, do not continue to reset repeatedly. Repeated restarts can cause further damage and will usually result in the boiler locking out again.

When to call a professional (and what to tell them):

- Call a Gas Safe registered engineer if the fault persists after bleeding radiators and repressurising, if pressure falls repeatedly, if the pump appears seized, if there are any leaks, if the boiler locks out repeatedly, or if there are electrical or gas supply concerns. Provide the engineer with the exact fault code/description, the steps you have already taken (bled radiators, pressure reached X bar, reset attempted), and any unusual noises or symptoms.

Final notes:

- Do not attempt internal repairs, sensor replacements, or electrical work yourself. These require a qualified engineer and may be dangerous or invalidate warranties.

- Keep a log of times and actions taken to help the engineer diagnose the root cause quickly.