Error 3 green flashes

Safety first:

- If you smell gas (rotten egg odour) do not touch the boiler or electrical switches. Turn off the gas at the meter if it is safe to do so, ventilate the area, leave the property and call the national gas emergency number immediately.

- Do not open the boiler casing or attempt internal repairs. Only a Gas Safe registered engineer should work on gas or internal combustion components.

- If you need to thaw a frozen condensate pipe, switch the boiler off at the control and isolate electrical supply at the wall before attempting to warm the pipe. Do not use boiling water.

Initial checks a homeowner can do:

1. Look at the boiler display and confirm it is showing three green flashes and then whether it clears or moves to three red flashes.

2. Check that the boiler has power (display lit) and that the thermostat/timers are calling for heat. Make sure any external controls (room stat, programmer) are set correctly.

3. Check other gas appliances (hob, gas fire) to confirm there is gas supply to the property. If they don’t work, check a prepayment meter credit or contact your gas supplier.

4. Check system pressure on the boiler gauge. Baxi boilers typically need roughly 1–1.5 bar when cold. If pressure is low (below ~1.0 bar) top up using the filling loop following the manufacturer instructions.

5. Inspect the external flue terminal for obvious blockages (nests, debris) and check any visible condensate discharge pipe for freezing in cold weather.

Step-by-step diagnostic and simple fixes to try:

1. Clear external obstructions: remove any obvious blockage from the flue terminal and make sure vents are not blocked. If you clear something, reset the boiler and observe.

2. Check condensate pipe (if present and external): in freezing weather a blocked/ frozen condensate pipe can cause ignition issues. With the boiler and mains power off, carefully thaw the pipe with warm (not boiling) water or a hot water bottle, then restore power and reset.

3. Top up system pressure if low: follow the boiler manual to use the filling loop until pressure is within the recommended range (usually around 1–1.5 bar cold), then reset the boiler. Do not over-pressurise.

4. Reset the boiler: press and hold the reset button (or follow your model’s reset procedure) for 5–10 seconds. The boiler will attempt to relight. Watch the sequence: a single, isolated 3-green-flash event that clears after reset can be left under observation.

5. Observe behaviour: allow the boiler to attempt normal operation. If the green flash repeats occasionally but clears, make a note of conditions (time, weather, whether DHW or CH was running). If the boiler fails to light repeatedly or the indication changes to three red flashes (ignition lockout), stop attempting resets.

When to call a professional:

- If the boiler shows three red flashes or repeatedly resets and returns to the same fault. Three red flashes indicate persistent ignition failure and requires a Gas Safe engineer.

- If topping up pressure, clearing the flue or thawing the condensate pipe does not resolve the issue.

- If you detect gas smells, any water leaks, electrical faults, loud unusual noises from the boiler, or if the boiler is otherwise unstable.

What the engineer may check or replace (for information only):

- Gas supply pressure and continuity, ignition electrodes and leads, flame sensor/ionisation probe cleaning or replacement, gas valve condition, fan/flue components, PCB/combustion module issues and chamber seals. These are specialist tasks for a qualified engineer.

Additional advice:

- Do not keep resetting the boiler repeatedly; repeated resets can cause further issues and will not replace a proper diagnosis.

- Keep a short log of when the fault happened, what you tried, and whether other gas appliances were affected—this speeds up diagnosis for the engineer.

- If in any doubt or if the problem persists, arrange a visit from a Gas Safe registered engineer to inspect and repair the boiler safely.