This fault can involve incomplete combustion and carbon monoxide.
If anyone in the property feels sick, dizzy or drowsy, or you can smell gas: open the windows, leave the building, and do not switch anything on or off. Then call the National Gas Emergency Service.
0800 111 999Potterton E135 fault codewhat it means and how to fix it
The Assure and Promax Ultra's internal-error ignition code: the control blames its own side of the gas valve rather than the supply for the flame that never came. One reset; then an engineer.
Take care
Did the gas supply change at the same time?
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.
Yes — meter work, credit ran out, other appliances were off
The boiler caught the interruption. One reset should be the end of it.
Reset once after the gas is back.
No, everything else was fine
Valve or board.
Engineer; expect the gas valve or PCB to be tested.
What E135 means
Potterton's digital-display manuals introduce 133, 134 and 135 with one sentence that covers all three — gas not reaching the burner, an ignition that did not take, or a flame the electrode never saw — and then tell them apart in the table. The row for 135 names an interruption of the gas supply and marks it as an internal error: the control has decided the reason no flame appeared lies on its own side of the gas valve rather than in the supply. It is on both manuals' reset list — a one-to-three-second press — and the Assure Combi user guide shows it with the R symbol.
The Promax and Titanium tables do not have it. The Assure System install manual's fault-finding chart reaches these codes together, at the box for 133, 134, 135 or 384 flashing, and sends the engineer to sections F and G, which is the gas valve supply (230 V across PCB connector X3 terminals 1 and 2, then replace PCB or valve) and the ignition electrode.
A note at the top of the same chart deals with 09, 15, 110 and 384 when they flash or keep coming back: the engineer goes over every connection on the board first, and changes the board only if that does not cure it. In practice 135 belongs in that company: an internal-error code that keeps returning after the gas supply has been confirmed is a valve or board fault, not something a householder can help.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| Valve not answering the board's drive | The valve (part 7683968 on the Assure) is driven by the board; a coil or connector fault means the board opens it and nothing happens. | Common |
| Gas actually off at the moment of ignition | Supply interrupted mid-sequence — a meter that cut off, a prepayment credit ending, air in a newly reconnected supply. The control has no way of separating this from a fault of its own. | Occasional |
| PCB | The Assure System installer manual's standing instruction for recurring internal codes: connections on the board first, then the board. | Occasional |
What to try yourself
Confirm the gas is on at another appliance and the meter has credit.
Press Reset for about one second. If the boiler lights and stays lit, watch it over the next day.
If 135 returns, or the boiler will not reset, contact your installer or Baxi Customer Support with the code. Do not repeat the reset.
Get a Gas Safe registered engineer to look at your Potterton E135
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.
What it costs to fix
Typical repair cost
£0–£320
Time on site
5 minutes
Nothing to pay when the supply was at fault. Gas valve £190–£300 fitted. PCB £220–£320.
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.
Baxi / Potterton / Main gas valve
7683968£120–£240Authorised Baxi parts distributor
Price checked 28 September 2026
Baxi / Potterton / Main main PCB
£150–£320Authorised Baxi parts distributor
Price checked 28 September 2026
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Related Potterton fault codes
- E133Get it checkedGas supply interrupted, ignition failed or no flame detected — every Potterton generation. Confirm the gas supply, one reset (5 s on the knob, 1–3 s on the button), and call if it returns.Related: ignition and gas supply
- E128Get it checkedFlame failure during normal operation on the Potterton Assure and Promax Ultra: the burner was lit and went out. Resettable; recurring E128 wants an engineer.Related: ignition and gas supply
- E09Get it checkedThe Assure and Promax Ultra's gas valve connection cable fault: the board has lost its wiring link to the valve. Resettable once; recurring 09 is a wiring or PCB job.Related: ignition and gas supply
- Red light flashingGet it checkedPotterton Assure Heat, Titanium Heat and Ultra Heat have no display: the illuminated button flashes red a number of times when the boiler has locked out. The count is the code.Related: ignition and gas supply
- E15Get it checkedThe Assure and Promax Ultra's own-valve code: the board has detected a fault in the gas valve itself, not its cable. One reset allowed; then an engineer with a meter.Related: ignition and gas supply
- E384Get it checkedThe Assure and Promax Ultra report a flame signal while the gas valve is shut. An electrode or PCB fault, and the Assure manual's answer is to go over the board.Related: ignition and gas supply
Own a Potterton boiler? Save it and its codes come first next time.
Related guides
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
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.