Baxi E128 Fault Code: Causes, Fixes & Repair Costs
What does the Baxi E128 fault code mean?
The E128 code appears on Baxi boilers when the appliance has tried to light the burner multiple times — up to 12 ignition attempts — but has been unable to sustain a stable flame. Rather than continuing to try indefinitely, the boiler locks out as a precaution, stopping the gas supply until the underlying problem is identified and resolved. You may have noticed the boiler firing up briefly before cutting out, or it may simply display E128 without lighting at all. Common triggers include a frozen condensate pipe in cold weather, a disrupted gas supply, or a worn ignition or flame-sensing electrode — but internal faults with the burner, gas valve, or PCB can also be responsible.
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
- Frozen condensate pipe Common
During cold snaps the plastic condensate pipe that runs outside (or through an unheated space) can freeze solid, causing a blockage that forces the boiler to shut down. Baxi themselves list this as a key trigger for E128, particularly in winter. The boiler may attempt to ignite, sense something is wrong, and lock out with this code.
- Gas supply interruption Common
If the gas pressure at the boiler falls below what the burner needs, the flame will either fail to light or will extinguish shortly after ignition. This can be caused by the gas meter isolation valve being partially closed, a problem with the local gas network, or other high-demand appliances drawing down pressure simultaneously.
- Faulty or dirty flame-sensing electrode Common
The flame rectification electrode sits inside the combustion chamber and confirms to the PCB that a flame is present. If it becomes coated in deposits, corroded, or develops a hairline crack, it may send a false 'no flame' signal even when the burner has lit — causing the boiler to cut the gas and lock out with E128.
- Worn or misaligned ignition electrodes Sometimes
The spark electrodes initiate combustion by generating a high-voltage spark across a precise gap. If the tip is eroded, the ceramic insulator is cracked, or the electrode has shifted out of position, the spark may be too weak or misplaced to ignite the gas reliably, leading to repeated failed attempts and lockout.
- Blocked burner or injectors Sometimes
Debris, scale, or corrosion within the burner assembly or the small gas injector jets can restrict the gas-air mixture reaching the flame. Because the jets are very narrow, even a small particle can be enough to cause unstable combustion or prevent the flame from establishing properly.
- Flue or air intake obstruction Sometimes
The boiler needs a clear path to draw in fresh air and expel combustion gases. A bird's nest, leaf debris, ice, or a kinked flue terminal can starve the burner of oxygen, causing the flame to extinguish during operation and triggering repeated lockouts.
- Faulty gas valve Rare
The gas valve controls the precise flow of gas to the burner. If it sticks, fails to open fully, or develops an internal fault, it can deliver insufficient gas to maintain combustion. This is a less common cause but should be considered if all other checks prove inconclusive.
- PCB or wiring fault Rare
The printed circuit board orchestrates ignition sequencing, flame sensing, and gas valve operation. Damaged wiring connections or a failing PCB can disrupt any part of this sequence, producing an E128 even when the physical components are in good order.
How to fix it
- Check that other gas appliances are working DIY safe
Try a gas hob ring or gas fire. If nothing is working, the issue is likely with your gas supply rather than the boiler itself. Check that the meter isolation valve handle is inline with the pipe (open), then contact your gas supplier if there is no supply to any appliance.
- Thaw a frozen condensate pipe (winter months) DIY safe
Locate the white or grey plastic condensate pipe — it usually exits through an external wall and terminates near a drain. If the weather is below freezing and the pipe feels solid, warm it gently along its exposed length using warm (not boiling) water from a watering can, a hot water bottle, or a microwaveable heat pack. Work from the boiler end towards the outlet. Once thawed, reset the boiler.
- Reset the boiler DIY safe
On most Baxi models, turn the central selector dial to the 'R' (Reset) position, hold for at least five seconds, then release. The display should revert to the current temperature. If the boiler lights and runs normally, monitor it over the next 24 hours. If E128 returns after two or three resets without improvement, stop resetting and move to the next steps — repeated lockouts indicate a fault that needs diagnosis.
- Inspect the flue terminal for obvious blockages DIY safe
Go outside and visually check the flue outlet (the white pipe terminating on an external wall or through the roof). Look for any obvious obstruction such as a bird's nest, ice build-up, or debris. Do not insert anything into the flue. If you can safely see and remove an obvious external blockage without touching any boiler components, do so, then reset.
- Have a Gas Safe engineer inspect the ignition and flame-sensing electrodes Gas Safe engineer
A registered engineer will remove the combustion chamber cover, check the spark electrode gap and condition, test the flame rectification electrode for continuity, and clean or replace either component as needed. This is not a DIY task — it involves working inside the sealed combustion chamber.
- Have the burner and injectors professionally cleaned or replaced Gas Safe engineer
An engineer can remove the burner, check the injector jets for blockage or corrosion, and clean or replace them. Correct reassembly and gas-tightness testing must follow, which requires Gas Safe registration and specialist tools.
- Have the gas valve tested and replaced if necessary Gas Safe engineer
An engineer will measure gas pressure and test valve operation. If the valve is sticking or not opening to the correct degree, it must be replaced by a Gas Safe registered professional — this is a regulated gas-fitting task.
- Have the PCB and wiring loom inspected Gas Safe engineer
If all physical components check out, the engineer will test the control board and associated wiring for faults. PCB replacement is a specialist task and should only be undertaken after eliminating all other causes, as the board is one of the more expensive parts on the boiler.
- Call a Gas Safe registered engineer if the fault persists Gas Safe engineer
If your own checks (gas supply, condensate, flue, reset) have not resolved E128, book a Gas Safe registered heating engineer to carry out a full diagnostic. You can verify an engineer's registration at gassaferegister.co.uk. Do not continue attempting to reset a boiler that repeatedly locks out, as this can mask a worsening fault.
Parts you may need
- Flame rectification (ionisation) electrode · from £25
- Ignition electrode · from £20
- Ignition lead set · from £18
- Burner assembly · from £85
- Gas injector / jet · from £15
- Gas valve · from £120
- PCB (printed circuit board) · from £220
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 £120–£350, depending on the underlying cause.
Frequently asked questions
Can I fix the Baxi E128 fault myself?
A few initial checks are safe to carry out yourself: confirming your gas supply is active, thawing a frozen condensate pipe, checking for obvious flue blockages, and resetting the boiler up to two or three times. However, if E128 persists after those steps, the cause almost certainly involves a component inside the boiler — such as the electrodes, burner, or gas valve — that must be inspected and repaired by a Gas Safe registered engineer.
How much does it typically cost to fix a Baxi E128 fault?
For the most common repairs — electrode replacement, burner cleaning, or a gas valve swap — most homeowners pay somewhere between £120 and £350 including labour and parts. A straightforward electrode or flame sensor replacement is usually at the lower end of that range. A gas valve or PCB replacement will push towards the higher end. In rare cases where the PCB has failed on an older boiler, costs can exceed £400; at that point it is worth getting a quote for a new boiler as a comparison.
Why does my Baxi boiler keep showing E128 every winter?
If E128 returns reliably in cold weather, the most likely cause is a frozen condensate pipe. The condensate pipe carries acidic water from the boiler to a drain; if any section runs outside or through an unheated space, it can ice up when temperatures drop below zero. The permanent fix is to insulate that exposed section with lagging. A Gas Safe engineer can do this during your annual service, or you can wrap the pipe yourself with pre-formed pipe lagging from a DIY store.
Is it safe to keep resetting the boiler when E128 appears?
Resetting once or twice to see whether a transient fault (such as a brief gas pressure dip) clears itself is reasonable. However, if the boiler relights and then locks out again shortly afterwards, or if E128 appears repeatedly over several days, you should stop resetting and call an engineer. Continually forcing restarts on a boiler that cannot maintain a flame can mask a deteriorating component and in some fault scenarios puts unnecessary wear on the ignition system.