Boiler keeps locking out: what to record and quick checks
Quick summary
Don’t keep resetting. Record the fault code and when it happens — that information often solves it faster.
Safety first
- Smell gas or suspect a leak: ventilate, leave the area, and call 0800 111 999.
- CO alarm sounding or anyone unwell: get fresh air and get urgent help.
- Do not remove boiler covers or attempt internal repairs.
- If there’s repeated overheating or scorching smells: switch off and get help.
Full checklist: Safety guidance
What to check (in order)
- Take a photo of the boiler display (fault code/symbol).
- Note when it happens: hot water only, heating only, or both.
- Check system pressure (sealed systems) and note cold reading.
- Check basic controls: thermostat/programmer calling for heat when expected.
- Reset once only, then see what happens immediately (does it fire? does it fail after a minute?).
What the result means
- Immediate re-lockout: hard fault likely (sensor, ignition/flame, fan/air, flow issues depending on code).
- Locks out after running: could be overheating/flow restriction, condensate issues, or intermittent components.
- Only on one mode (CH or DHW): helps narrow to that circuit/controls.
What you can safely do
- Take a photo of the fault code or display.
- Note whether the problem happens on heating, hot water, or both.
- Check system pressure and basic controls.
- Reset once only, then record what happens next.
When to call a professional
- Any gas smell/CO alarm/unsafe signs.
- Repeated lockouts (more than once) or recurring fault codes.
- Pressure issues alongside lockouts.
Engineer notes
Treat as evidence-first: code, mode, runtime-to-fault, and environmental conditions. Confirm supply voltage stability, gas rate (qualified), combustion parameters (qualified), and circulation (pump, bypass, filter, ΔT). If ignition/flame-related, check electrode/lead, gas valve control, and condensate trap condition (model dependent).
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