Overview
A 1 green flash on a Baxi MainEco means the boiler has reached its set temperature and is indicating a normal temperature-reached condition. This signal is informational rather than a fault indication; the boiler is modulating down or stopping because the thermostat or programmed set point has been satisfied. In normal operation you will often see this when heating or hot water reaches the target temperature and the burner is switching off or reducing output. Severity is low. No immediate repair is required if the heating and hot water are working as expected and no other fault lights are present. It is a DIY-friendly situation for basic checks and monitoring. However, if the green flash appears together with loss of heating/hot water, repeated rapid cycling, other error flashes (especially red ones), fluctuating system pressure, overheating symptoms, or unusual noises, that can point to a sensor, circulation or control issue and a Gas Safe registered engineer should be called to diagnose and repair the appliance.
Possible Cause: Boiler temperature reached – no action required
Troubleshooting Steps
Safety precautions:
- If you smell gas, evacuate the property and call the gas emergency number immediately. Do not operate electrical switches or the boiler.
- Do not remove the boiler casing or attempt internal repairs. Only qualified engineers should access internal components.
- Turn off power to the boiler at the isolator switch before touching external pipework or the filling loop if you are unsure about what to do.
Initial checks a homeowner can do:
- Check whether the central heating or hot water has actually reached the set temperature. The 1 green flash often simply means the set temperature is met.
- Check the boiler display for any other flashes or fault codes in addition to the single green flash.
- Check the system pressure gauge; it should normally be around 1 to 1.5 bar when cold. If it is below 1 bar or well above 2.5 bar, that needs attention.
- Look for visible leaks, water on or under the boiler, or cold radiators indicating circulation problems.
- Make sure room thermostat and programmer are set correctly and any timers are calling for heat when you expect.
- Ensure the external flue terminal is not blocked by debris, bird nests or snow.
Diagnostic and simple fix steps:
1) If the boiler has reached temperature and everything else works, do nothing and monitor. The green flash is normal.
2) If radiators or hot water are not working despite the green flash, check system pressure. If pressure is low (below about 1.0 bar), top up using the filling loop: locate the filling loop (usually under the boiler), open the valve(s) slowly until pressure rises to approximately 1.0–1.5 bar, then close valves and recheck. Only use the filling loop if you know how; if unsure, call an engineer.
3) Bleed radiators to remove trapped air which can stop circulation. After bleeding, recheck and top up pressure if it drops.
4) Reset the boiler if you suspect a temporary sensor or communication glitch. Use the boiler reset button or selector (press and hold the reset for 5 to 10 seconds, or set the selector to R for models with that control). Wait and observe whether the boiler restarts normally. Do not repeatedly reset if the problem returns.
5) If you see the 1 green flash accompanied by abnormal noises, the boiler getting excessively hot to the touch, frequent on/off cycling, or other fault lights appearing (especially red flashes), switch the boiler off and contact a Gas Safe registered engineer.
When to call a professional:
- If the 1 green flash is persistent and you are losing heating or hot water, or if other error codes appear.
- If system pressure keeps dropping or rising and you cannot find or stop a leak.
- If you experience repeated lockouts, red fault lights, ignition failures, or signs of overheating.
- For any internal sensor, PCB, fan or gas valve faults, or if you are uncomfortable performing the basic checks described above.
Do not attempt internal electrical or gas repairs. If in doubt, contact a Gas Safe registered engineer to inspect and diagnose the boiler.
Helpful Resources
Boiler Manual
Download the official PDF manual for the Baxi MainEco.