Overview
This fault (3 red flashes on Baxi 816/825/830 Heat models) is an ignition fault or flame failure. It means the boiler tried to light or was running and the burner flame was not detected or was lost, so the boiler has shut down for safety. Common reasons include no or interrupted gas supply, low gas pressure, faulty ignition electrodes or flame sensor, a failing gas valve, flue or ventilation problems, a blocked condensate drain or a false flame signal from a faulty sensor. Severity is moderate to high in the sense that the boiler will not provide heating or hot water while the fault persists and the boiler is intentionally locked out to prevent unsafe operation. If you smell gas or suspect a gas leak, that is an immediate emergency and you must act accordingly. Some basic checks are safe for a homeowner, but most diagnostic and repair work on ignition, gas valves, electrodes, flues and internal components must be carried out by a Gas Safe registered engineer.
Possible Cause: No ignition. No flame detected following ignition. False flame signal detected. Repeated loss of flame detected.
Troubleshooting Steps
Safety precautions:
- If you smell gas: leave the property immediately, do not operate electrical switches, do not use phones inside, call the gas emergency number from a safe location. Treat any gas smell as an emergency.
- Do not attempt internal repairs to gas pipes, valves, burner, electrodes or the PCB. These must be done by a Gas Safe engineer.
- Do not keep repeatedly resetting the boiler; repeated lockouts can indicate a dangerous fault and can damage components.
Initial checks a homeowner can do (safe, simple):
1) Check gas supply: confirm other gas appliances (hob) are working. If you are on a prepayment meter, check credit. If other appliances do not work, contact your gas supplier.
2) Check boiler power and controls: ensure the boiler is powered, programmer/thermostat calling for heat, and any external isolation switches are on.
3) Reset once: find the reset button (often a flame symbol or marked reset). Press and hold for 5–10 seconds, allow the boiler to attempt ignition. If it restarts and runs normally, monitor it. If the same fault returns, do not keep resetting.
4) Check condensate pipe/drain (common in cold weather): an external condensate pipe can freeze or internal condensate drains can block. If frozen, thaw the external pipe with warm (not boiling) water or a warm cloth. If you can see and safely access an external trap and it appears blocked, you can try to clear superficial debris; for internal condensate blockages, call an engineer.
5) Check external flue and air vents: ensure the flue terminal and any air vents are not blocked by debris, bird nests, snow or vegetation.
6) Note boiler pressure: while not the primary cause of flame failure, very low system pressure can prevent normal operation. Check the pressure gauge (aim normally for about 1–1.5 bar). Do not over-pressurise.
7) Visual earthing/power connection check: a loose earth or poor electrical connection can cause false flame signals. Visually check that the boiler is plugged in (if applicable) and that any external earth connections look intact. Do not open the casing to trace wiring.
Specific diagnostic/fix steps (if initial checks do not clear the fault):
1) If gas supply is confirmed but fault persists, stop further DIY checks. Contact a Gas Safe registered engineer. Provide the engineer with the boiler model, fault code (3 red flashes / ignition fault), when it occurs (on ignition, during running, intermittently), and whether you tried a reset.
2) The engineer will check: gas pressure at the appliance, gas valve operation, ignition electrode condition and gap, flame sensor performance, flue integrity and ventilation, condensate drain route, PCB fault codes and earthing/grounding. They may clean or replace electrodes, adjust combustion settings, replace a faulty flame sensor or gas valve, or repair flue/venting problems.
3) If the boiler returned to service after you thawed a condensate pipe or cleared an obvious external blockage, still have the system checked if the fault happens again; recurring flame failure often indicates a component starting to fail.
When to call a professional now:
- If you smell gas, call the gas emergency service immediately.
- If the fault returns after one reset, or the boiler locks out repeatedly.
- If you cannot identify a simple external cause (gas supply, frozen condensate, blocked flue) or if any internal components are suspected.
What to tell the engineer when you call:
- Boiler model and serial if available (Baxi 816/825/830 Heat), the fault code (3 red flashes / ignition fault), what you observed, any recent events (power cuts, very cold weather, loss of other gas appliances), and what you have already tried (reset, checked gas, thawed condensate, cleared flue). This helps the engineer diagnose and prioritise checks.
Summary: perform the safe basic checks listed above (gas supply, reset once, check condensate and flue) but do not attempt internal repairs. For persistent or repeated ignition faults, or any sign of gas smell, arrange an inspection and repair by a Gas Safe registered engineer.
Helpful Resources
Boiler Manual
Download the official PDF manual for the Baxi 816 Heat, 825 Heat, 830 Heat.