Overview
On a Baxi MainEco, 2 red flashes indicate an over-temperature or overheat trip. The boiler has detected that internal temperatures have exceeded safe limits and has shut down (locked out) to protect itself and your heating system. Common causes include poor water circulation (airlocks in radiators, closed valves, or a failed pump), high system pressure, a blocked or restricted heat exchanger or flue, or a frozen/blocked condensate/drain pipe in cold weather. Severity is moderate to high: the boiler is protecting itself so there is no immediate catastrophic risk from the fault itself, but the underlying cause can damage the boiler if ignored (e.g., pump failure or scale buildup) and you will be without heating/hot water until it is resolved. Simple user-level causes can sometimes be fixed safely at home, but failures involving gas, internal components, the pump, heat exchanger or PCB must be dealt with by a Gas Safe–registered engineer. If the fault clears after basic checks and a proper reset, monitor the boiler closely. If the error returns, occurs repeatedly, or you smell gas, do not attempt further repairs yourself — isolate the appliance and call a qualified engineer immediately.
Possible Cause: Boiler overheat tripped
Troubleshooting Steps
Safety precautions:
- If you smell gas, leave the property immediately and call your gas emergency number. Do not operate electrical switches or the boiler.
- Before any checks, switch the boiler off at the programmer/control and at the isolator or fuse spur. Allow the boiler to cool (30–60 minutes) before touching pipes or the casing.
- Do not remove the boiler casing or attempt internal repairs unless you are a Gas Safe–registered engineer.
Initial homeowner checks you can safely do:
1. Turn the boiler off and allow it to cool. Note any obvious signs: water leaks, unusual smells, or loud banging noises prior to lockout.
2. Check the system pressure on the boiler pressure gauge. Aim for roughly 1.0–1.5 bar when cold. If pressure is low (below about 1 bar), top up using the filling loop following the boiler manual, then reset the boiler. If pressure is too high (over 2.5–3 bar) you may need to bleed a radiator or call an engineer.
3. Bleed radiators to remove trapped air which can cause poor circulation and overheating. Start with the radiator closest to the boiler. After bleeding, recheck pressure and repressurise if needed.
4. Ensure all radiator valves (thermostatic and lockshield) and zone valves are open so water can circulate. Check that your programmer/thermostat is calling for heat appropriately.
5. Check the flue terminal outside the property for any visible blockage (birds’ nests, leaves, snow) and clear if it is safe to do so. Also inspect any visible condensate pipework for freezing or blockages (in cold weather thaw gently with warm water or lag the pipe). Do not pour boiling water on frozen pipes.
6. Listen for the circulation pump running when the boiler tries to fire (you may hear or feel a faint vibration on the pump housing). If the pump is silent and you have tried basic measures (bleeding radiators, checking valves) you will likely need an engineer.
Reset procedure (try once after the checks above):
- Use the boiler’s reset button (press and hold for 5–10 seconds) or follow your model’s reset method (turn selector to R for 5 seconds or turn the thermostat knob fully anticlockwise then back). Wait for the boiler to attempt to restart. Do not repeatedly reset more than 2–3 times if the fault persists.
What to watch for after reset:
- If the boiler restarts and runs normally, monitor for reoccurrence. If the error returns, note when it happens (after long run times, immediately on start, only when certain zones are on) and call an engineer.
- If the boiler will not reset, or resets and then immediately returns to 2 red flashes, stop attempting resets and arrange professional service.
When to call a professional:
- If bleeding radiators, topping up pressure, clearing flue/condensate and a single reset do not clear the fault.
- If the pump appears to have failed, there are signs of internal leakage, the pressure repeatedly drops, or the fault returns frequently.
- If you are uncomfortable performing any of the checks above or if the fault condition is unclear.
Important notes:
- Do not attempt internal electrical or gas repairs yourself. Working on gas appliances is dangerous and must be carried out by a Gas Safe–registered engineer.
- Repeatedly resetting the boiler without addressing the root cause can cause further damage. If the fault is not solved by basic user checks and one proper reset, book a Gas Safe service to diagnose pump, heat exchanger, sensor or PCB issues.
If you need help finding a qualified engineer, contact the manufacturer helpline or use the Gas Safe Register to locate a local professional.
Helpful Resources
Boiler Manual
Download the official PDF manual for the Baxi MainEco.