Baxi E131 Fault Code: Causes, Fixes & Repair Costs
What does the Baxi E131 fault code mean?
The E131 code means your Baxi boiler has detected that the flue gas temperature has climbed above its safe operating limit — specifically, the flue gas exceeding 85°C or the flow temperature sensor reading above 90°C will trigger this shutdown. The boiler locks out completely as a built-in safety measure to prevent damage and protect your home. It will not fire again until the fault has been acknowledged and, where necessary, resolved. Do not attempt to defeat or bypass the safety lockout — it exists for good reason.
General guidance only — not a substitute for professional advice. Any gas work must be carried out by a Gas Safe registered engineer. If you smell gas or suspect carbon monoxide, leave the property and call the National Gas Emergency line on 0800 111 999.
Common causes
- Blocked or obstructed flue terminal Common
The most frequent trigger. Leaves, debris, a bird's nest, or even compacted snow around the flue outlet on the outside wall can restrict exhaust gases from escaping. This causes heat to build up rapidly inside the flue, pushing temperatures past the safety threshold and locking the boiler out.
- Faulty or failing combustion fan Common
The fan is responsible for drawing combustion air in and pushing flue gases out. If it is running slowly, intermittently, or not at all due to worn bearings or a failing motor, flue gases linger and overheat. This is one of the more common component failures on Baxi boilers and typically requires a Gas Safe engineer to replace.
- Flue NTC temperature sensor fault Sometimes
A dedicated NTC thermistor monitors the flue gas temperature. If the sensor has drifted out of calibration, has a loose connection, or has failed entirely, it can report falsely high temperatures and trigger a lockout even when flue temperatures are within normal limits — or, conversely, fail to warn until genuine overheating occurs.
- Poor system circulation — trapped air or faulty pump Sometimes
If air is trapped in the radiators or the circulating pump is sluggish or seized, water cannot flow around the heating circuit efficiently. Heat builds up in the heat exchanger and flue rather than being distributed around the system, which can raise flue temperatures enough to trigger E131.
- Incorrect or poorly maintained flue installation Sometimes
A flue that was fitted incorrectly — wrong length, wrong angle, inadequate clearances, or joints that have worked loose over time — can create back-pressure or allow hot gases to recirculate, causing localised overheating. This is more common on older installations or after building work near the flue.
- Transient power cut or voltage disturbance Sometimes
A brief power interruption can confuse the boiler's control board, causing it to latch into a fault state even though no genuine overheat event occurred. A single reset usually clears this, but if the fault returns after a reset, a deeper cause should be investigated.
- Smart thermostat or wiring communication error Rare
Incorrectly wired or misconfigured smart thermostats can send erratic signals to the boiler's PCB, occasionally resulting in a spurious lockout. This is relatively uncommon but worth considering if the fault appeared shortly after a new thermostat or control was installed.
How to fix it
- Check the gas supply is working DIY safe
Before anything else, confirm that other gas appliances in your home — hob, gas fire — are working normally. If there is no gas supply to the property, contact your gas supplier rather than resetting the boiler.
- Inspect the external flue terminal for obvious blockages DIY safe
Go outside and look at the flue outlet on the wall or roof. Remove any visible debris, leaves, or bird-nesting material from around the terminal grille. Do not attempt to dismantle the flue pipe itself — simply clear external obstructions you can safely reach.
- Bleed the radiators to remove trapped air DIY safe
Use a radiator bleed key to open the bleed valve on each radiator, starting with the ones furthest from the boiler. Hold a cloth under the valve and release air until water flows steadily, then close the valve. Repeat for all radiators. When finished, check the boiler pressure gauge — it should read between 1.0 and 1.5 bar when the system is cold. If it has dropped below 1 bar, top it up using the filling loop.
- Top up system pressure if it has dropped DIY safe
Find the filling loop (usually a braided hose with one or two valves beneath the boiler). Slowly open the valve(s) and watch the pressure gauge climb to around 1.2–1.5 bar, then close the valve(s) firmly. Never pressurise above 1.5 bar when cold.
- Reset the boiler once DIY safe
On most Baxi models, reset by turning the temperature control knob fully anticlockwise until the lockout light extinguishes, then returning it to your desired setting. On models with a dedicated reset button, press and hold for three seconds. Allow the boiler to complete a full start-up cycle and monitor it for the next hour. Only reset once — if the E131 code returns, stop resetting and move to the next step.
- If the fault persists, call a Gas Safe registered engineer Gas Safe engineer
A recurring E131 code almost always points to a component that needs professional diagnosis — most commonly a failing fan, a faulty flue NTC sensor, or a flue installation issue. A Gas Safe engineer will carry out combustion and flue temperature checks, test the fan speed and current draw, inspect sensor readings on the PCB, and advise on repair or replacement. Do not remove the boiler casing, interfere with the flue pipework, or attempt any internal repairs yourself.
Parts you may need
- Combustion fan assembly (Baxi) · from £95
- Flue NTC temperature sensor · from £25
- Circulating pump · from £75
- PCB (printed circuit board) · from £180
The exact spare depends on your boiler's GC number (on the data badge). Check this against the part before buying.
Typical repair cost
Expect to pay roughly £150–£400, depending on the underlying cause.
Frequently asked questions
Can I just keep resetting my Baxi boiler to clear the E131 code?
One reset is fine — it clears a transient fault such as a momentary power blip. However, if the boiler locks out again with E131 shortly after the reset, you should stop. Repeated resets will not fix the underlying problem and could mask a genuine flue overheating issue, which is a safety concern. At that point, call a Gas Safe registered engineer to investigate properly.
How much does it typically cost to repair a Baxi E131 fault in the UK?
Most people with this fault end up paying somewhere between £150 and £400, which usually covers the call-out, diagnosis, and either a fan replacement or a sensor replacement with labour. If both the fan and PCB need replacing together, costs can rise to £500–£650. Heat exchanger replacement is rare but can push costs higher still — worth factoring in on an older boiler when deciding whether to repair or replace.
Why has my flue overheated — is it dangerous?
The E131 lockout is the boiler protecting itself and your home. An overheating flue can indicate that combustion gases are not being expelled efficiently, which in a worst-case scenario could relate to carbon monoxide risk. Ensure your CO alarm is working. Do not run the boiler in a locked-out state, and do not tamper with the flue. Get a Gas Safe engineer to confirm the flue is sound before returning the boiler to normal use.
Will an annual boiler service help prevent the E131 code coming back?
Yes, significantly. A yearly service includes checking fan performance, inspecting the flue for partial blockages or joint deterioration, verifying sensor readings, and cleaning components that affect combustion. This is the single most effective way to catch the conditions that lead to E131 before they cause a breakdown. Baxi's own service starts from around £96; independent Gas Safe engineers are often comparable in price.