Baxi E135 Fault Code: Causes, Fixes & Repair Costs
What does the Baxi E135 fault code mean?
The E135 fault code on Baxi boilers indicates an internal gas supply interruption, placing the boiler into a safety lockout. Rather than pointing to a problem with your home's gas supply itself, this code signals that something within the boiler's own gas handling or control system has failed — the boiler has detected it cannot safely process gas and has shut itself down as a precaution. On some Baxi models, particularly the GA range, E135 is more specifically associated with a PCB-level error, while on others it may present alongside an ignition lockout. In all cases, the boiler will stop producing heat and hot water until the underlying fault is identified and resolved.
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
- Internal gas valve fault Common
The gas valve controls the flow of gas into the burner. If it develops an electrical or mechanical fault — such as a failed solenoid coil, a wiring break, or a stuck mechanism — the boiler's control system will detect the anomaly and trigger E135. This is one of the most common root causes engineers find when investigating this code.
- PCB (printed circuit board) failure Common
The PCB acts as the boiler's central control unit, coordinating all components including the gas valve and ignition system. A fault on the PCB — whether due to a component failure, moisture ingress, or a power surge — can cause it to incorrectly report an internal gas interruption and lock the boiler out with E135.
- Ignition system failure Sometimes
If the ignition electrode, lead, or spark generator fails, the boiler may attempt to fire, detect no flame, and interpret this as a gas supply issue internally. Repeated ignition failures can result in an E135 lockout rather than a more specific ignition fault code, depending on the model.
- Empty prepayment meter or external gas interruption Sometimes
Although E135 is classed as an internal error, it can occasionally be triggered if the boiler fires up and finds no gas at all — for example, if a prepayment meter has run out of credit or there is a temporary interruption from the gas network. This is worth ruling out first as it requires no engineer.
- System sludge or contamination Rare
A build-up of magnetite sludge or debris in the heating system can restrict flow and cause the boiler to behave erratically, potentially contributing to intermittent faults including E135. This is more likely in older systems that have never been power-flushed or had inhibitor added.
How to fix it
- Check your gas supply DIY safe
Before anything else, confirm that other gas appliances in your home — such as a gas hob or gas fire — are working normally. If they are not, contact your gas supplier or call the National Gas Emergency Line on 0800 111 999. If you are on a prepayment meter, check that it has sufficient credit. This simple check can save you an unnecessary call-out fee.
- Reset the boiler DIY safe
If your gas supply is confirmed to be fine, try resetting the boiler. On most Baxi models, turn the selector dial to the 'R' (Reset) position and hold it there for approximately 5 seconds, then release. The boiler will attempt to restart. If it fires up successfully, monitor it over the next few hours. Limit resets to two or three attempts — repeatedly resetting without resolution will not fix the underlying fault and could mask a safety issue.
- Call a Gas Safe registered engineer Gas Safe engineer
If the E135 code returns after resetting, or if the boiler fails to restart at all, you need a Gas Safe registered engineer. They will carry out a full diagnostic — checking the gas valve, its wiring and electrical connections, the PCB, and the ignition components — to pinpoint the exact cause. Do not attempt to open or repair any internal gas components yourself. You can verify an engineer's Gas Safe registration at gassaferegister.co.uk.
Parts you may need
- Gas valve · from £95
- PCB (printed circuit board) · from £220
- Ignition electrode · from £18
- Ignition lead · from £15
- Gas valve wiring harness · from £25
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–£380, depending on the underlying cause.
Frequently asked questions
Can I fix the Baxi E135 fault myself?
The only safe DIY steps are checking that your gas supply is active (including your prepayment meter if you have one) and performing a boiler reset as described above. Everything beyond that — inspecting or replacing the gas valve, PCB, or ignition components — must be carried out by a Gas Safe registered engineer. Working on internal gas components without the correct qualifications is illegal and dangerous.
How much will it cost to fix a Baxi E135 fault?
For the most common causes, expect to pay roughly £150–£380 including parts, labour, and any diagnostic fee. A gas valve replacement typically falls in the £150–£300 range, while ignition system components are usually £100–£250. If the fault turns out to be the PCB, costs are higher — PCB replacement on a Baxi boiler typically runs £450–£700 depending on the model and your location in the UK. If the PCB quote seems steep, it is worth comparing the cost against a new boiler, particularly if your boiler is over 10 years old.
Why does my Baxi boiler keep showing E135 and then clearing itself?
An intermittent E135 — where the fault disappears after a reset but keeps coming back — is a strong sign of an underlying component fault rather than a one-off glitch. Common culprits include a gas valve that is starting to fail, a PCB with a developing fault, or a loose wiring connection. These faults rarely resolve on their own and tend to worsen over time, often cutting off heating or hot water at inconvenient moments. Book an engineer sooner rather than later to avoid a full breakdown in cold weather.
Is my Baxi boiler still under warranty?
Baxi offers a minimum 2-year warranty on new boilers, which can extend to up to 10 years if installed by a Baxi-accredited installer. To keep the warranty valid, the boiler must have been serviced annually by a Gas Safe registered engineer. If your boiler is within its warranty period and has been serviced correctly, contact Baxi directly before arranging an independent repair, as the cost of parts or labour may be covered.