Baxi E128 fault codewhat it means and how to fix it
Flame failure while the burner was running, on the digital-display Baxis. The boiler relights itself unless it keeps happening; Baxi's manuals name gas supply, electrode and flue as the things to check.
Take care
Get a Gas Safe registered engineer to look at your Baxi E128
We do not pass enquiries to a repair firm, so there is no form here. Find a Gas Safe registered engineer through the Gas Safe Register, and ask to see their registration card when they arrive — it is the register, not the van, that tells you they are qualified.
When does the flame go out?
The right answer depends on what you can see. Pick the one that matches.
Choose the option on the left that matches what your appliance is doing, and the answer for that case appears here.
Only in freezing weather
Condensate is backing up because the outside pipe is partly iced. The flame dies when water reaches the combustion side.
Thaw the external pipe with warm water and reset once. Have the pipe insulated or re-routed if it recurs.
When a tap is running or the boiler is at full output
Gas pressure or the valve setting cannot hold the flame at high fire. Both are engineer checks with a manometer and analyser.
Book a service and mention when it happens.
At random, in any weather
Electrode or flue. Neither is visible from outside the case.
Engineer visit; ask for the electrode and the flue seals to be checked.
What E128 means
E128 is printed only on Baxi's digital-display generation — the Duo-tec 2, the Compact ranges, the 600 and 800, Assure, Megaflo System and EcoBlue — and the 600 and 800 manuals define it in one sentence: "128 is displayed if there has been a flame failure during normal operation." That distinguishes it from E133, which is a failure to light in the first place.
With E128 the burner was alight and the flame signal went. The EcoBlue Advance user guide labels the same number "Flame Failure (no lock-out)", which is the useful clue: on its own E128 is a report, and the boiler retries. It is also one of the codes the 600 and 800 manuals say can be relit from the panel: "By pressing the Reset button for 1 to 3 seconds when 09, 15, 110, 125, 128, 133, 134, 135, 384 are displayed it is possible to relight the boiler." Baxi's professional table adds two neighbours you may see instead. E129 is "Safety error for frequent loss of flame with max correction during ignition during Calibration Function" — the same problem caught while the board was calibrating the gas valve — and the EcoBlue Advance prints E151 as a straightforward "Flame Failure" alongside E128.
A flame that lights and then dies points at whatever is disturbing it: gas pressure sagging when other appliances run, a flue that is letting exhaust back to the air inlet, a condensate trap or pipe partly blocked so that water backs up into the combustion side, or a sensing electrode that is losing the signal as it heats. The 600 Combi fault-finding flow for a burner that "does not stay alight" checks the gas valve setting (CO2), then the sensing electrode and its lead and position, then the board.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| Condensate backing up | A partly frozen pipe or a trap full of debris lets water rise into the burner space and snuff the flame mid-cycle. It clears, the boiler relights, and it happens again an hour later. Baxi's 600 user guide lists "condensate drain blocked" among the things to check when the boiler stops. | Common |
| Flame-sensing electrode losing the signal | The electrode reads the flame through a small current. As it wears or coats with deposit the signal weakens, and the board decides the flame has gone while it is still burning. Baxi's flow checks the sensing electrode, its lead and its position. | Common |
| Gas pressure dropping under load | The 600 and 800 manuals want 19 mbar minimum at the meter. An undersized supply or a partly closed cock can hold a flame at low fire and lose it as the burner ramps up. | Occasional |
| Flue recirculation | A flue terminal in a sheltered corner, a damaged seal or a joint that has moved can feed exhaust back to the air inlet. The flame lights on clean air and dies as the recirculated gas builds. | Occasional |
| Gas valve setting drifted | Baxi's first check for a burner that goes out is the set of the gas valve against the CO2 values in the manual. It is a combustion-analyser adjustment, not a screwdriver one. | Rare |
Can you fix it yourself?
Stop — this needs an engineer
What it costs to fix
Typical repair cost
£0–£350
Time on site
45 minutes
Free if thawing the condensate pipe clears it. Electrode (Baxi 7686344) fitted £110–£180. Flue seal or terminal work £120–£250. Gas valve adjustment is part of a service; replacement £280–£450.
Typical UK prices including parts and labour, updated September 2026. Your quote may differ.
Parts you may need
We may earn a commission if you buy a part through one of these links. It does not change what you pay, and it does not affect which parts we list.
Condensate trap and siphon
COND-TRAP£15–£38Plumbing merchant
Price checked 28 September 2026
Baxi / Potterton / Main detection and spark ignition electrode
7686344£25–£60Authorised Baxi parts distributor
Price checked 28 September 2026
Baxi / Potterton / Main gas valve
7683968£120–£240Authorised Baxi parts distributor
Price checked 28 September 2026
Own this appliance and had this code? . Nothing is published until a person has read it.
Related Baxi fault codes
- E133Get it checkedBaxi's ignition lockout: "the gas supply has been interrupted, ignition has failed or the flame has not been detected". Check the gas is on, reset once. If it returns, stop.Related: ignition and gas supply
- E.04.10Get it checkedIgnition failure on the Baxi 200/400 Combi and every Combi 2: the burner would not light after its allowed attempts. Baxi's own quick guide names it the frozen-condensate code you can fix yourself.Related: ignition and gas supply
- E134Get it checkedBaxi's "elapsed time — gas valve open without gas": the valve opened, nothing arrived. Check the meter and credit before anything else; it resets from the panel.Related: ignition and gas supply
- E.01.04Stop — call an engineer"Flame loss detected five times in 24 hours": the burner keeps lighting and going out on a Baxi 200/400 Combi or Combi 2. Gas pressure, valve calibration, flue or electrode — an engineer's list.Related: ignition and gas supply
- E09Get it checkedGas valve connection cable fault on the 600, 800, Compact and Duo-tec 2. The board cannot talk to the valve. Baxi allow one reset; a repeat means the wiring or the PCB.Related: ignition and gas supply
- E135Get it checkedBaxi's "interruption of gas supply (internal error)". Same family as E133 and E134 but the manual calls it internal, so a reset that fails means the board or gas valve circuit.Related: ignition and gas supply
Own a Baxi boiler? Save it and its codes come first next time.
Related guides
Common questions about Baxi E128
Can I reset E128 myself?
Yes. It is in Baxi's list of codes that can be relit with the Reset button held for one to three seconds (two seconds on the EcoBlue Advance). If it comes back the same day, the cause needs finding rather than clearing.
What is the difference between E128 and E133?
E133 is a failure to light: three attempts, no flame, lockout. E128 is a flame that was burning and went out during normal operation. Baxi define both in the 600 and 800 manuals and they point at different things — supply and ignition for E133, flame stability for E128.
What are E129 and E151?
E129 is on Baxi's professional table as repeated flame loss caught during the gas valve calibration function; treat it as E128 with the calibration to be redone. E151 is printed only on the EcoBlue Advance as "Flame Failure", where E128 is the no-lockout version of the same event.
Technical review
Not reviewed by an engineer
No engineer has read this page. Severity follows what the manufacturer publishes, and we would rather tell you that than let a byline imply a sign-off.
Sources and how we verified this
We establish the facts from the sources below and then write the explanation ourselves. We do not copy manufacturer wording and we do not host their manuals.
- Manufacturer technical and service documentation
- Manufacturer support portal
This page has not been reviewed by an engineer, and we would rather tell you that than imply otherwise. The severity rating follows what the manufacturer publishes: where they say isolate the appliance and call someone, so do we.