Potterton E133 fault codewhat it means and how to fix it
Ignition failed and the appliance has locked out. On a Promax the condensate run is the first thing to check in cold weather.
Take care
When did it stop working?
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.
First thing in the morning, and it is freezing outside
This is the classic frozen condensate signature on a Promax. It is genuinely likely you can fix it yourself in twenty minutes with a kettle and some patience.
Thaw the external condensate run, reset, and arrange for the pipe to be lagged before the next cold spell.
The weather is mild and it has just stopped
Freezing is ruled out. That leaves the gas supply, a worn electrode, or a silted condensate trap inside the appliance — and only the first is something you can check.
Confirm other gas appliances work. Reset once, and if it locks out again book a Gas Safe engineer rather than continuing.
It has been intermittent for weeks and is getting worse
A gradual decline is the signature of a wearing part rather than a sudden failure, and on an appliance of this age that usually means the ignition electrode.
Book a service rather than a repair. An electrode is a modest cost and having it done alongside a proper service is better value than an emergency call-out in the middle of a cold snap.
What E133 means
E133 is an ignition fault: the appliance ran its sequence and never confirmed a flame. There is a specific reason this code dominates Potterton call-outs every January. A great many Promax appliances were fitted in flats and terraced properties where the condensate could not be run to an internal drain, so it goes out through the wall and down the outside — often a long horizontal run with very little fall on it, sometimes in 21mm pipe that should have been upsized. That arrangement freezes readily. The appliance then produces condensate it cannot discharge, the trap floods back towards the combustion chamber, and ignition fails within a minute or two of the first attempt of the morning. The pattern is characteristic: it worked fine last night, it will not light at seven in the morning, and by mid-afternoon when the sun has been on the pipe it works again. If that describes your appliance, you almost certainly have a condensate problem rather than an ignition one.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| Condensate pipe frozen | Dominant on Promax installations because of the long external runs typical of the era. Classic signature is failing first thing in the morning and recovering later in the day. | Common |
| No gas at the appliance | Prepayment meter out of credit is very common in the rented properties where these appliances concentrate. Check whether the hob lights before anything else. | Common |
| Ignition electrode worn out | A consumable part with a service life of roughly a decade. On a fifteen-year-old appliance that has never had one fitted, it is overdue rather than unlucky. | Common |
| Condensate trap silted internally | Separate from the pipe freezing. The trap inside the appliance fills with debris over years and stops draining, producing the same symptom in any weather. | Occasional |
| Gas valve failing | The dearest possibility. Suspect it last, once the supply, the condensate and the electrode have all been eliminated. | Rare |
What to try yourself
Try a gas hob ring first. If it will not light, the problem is the gas supply and nothing you do to the boiler will help.
Check the prepayment meter if you have one, including whether emergency credit ran out overnight.
Go outside and follow the condensate pipe. On a Promax this is often a long run along the wall before it drops — walk its whole length feeling for a solid, ice-cold section, not just the bit near the boiler.
Pour hand-hot water slowly along the frozen part, working from the open end back towards the appliance so the melt has somewhere to escape.
Never boiling water, never a heat gun, never a naked flame. Cold plastic cracks readily, and a split condensate pipe in January is a much worse position than a locked-out boiler.Open the front flap, hold reset for five seconds, and call for heat. If it fires and stays running, the condensate was the cause — get the pipe lagged and, if it is a long horizontal run, ask about upsizing it.
Get a Gas Safe registered engineer to look at your Potterton E133
Gas Safe Register engineers only. No obligation.
What it costs to fix
Typical repair cost
£0–£320
Time on site
30 minutes
Free if it is a frozen pipe you thaw. Lagging and upsizing an external condensate run is £120 to £280. An ignition electrode is £110 to £190 fitted, and a gas valve £240 to £320.
Typical UK prices including parts and labour, updated August 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 5 August 2026
What other owners found
Nobody has shared what worked for them on this code yet. If you have had it, you would be the first — and it genuinely helps the next person.
Related Potterton fault codes
- E128Get it checkedThe flame was established and then repeatedly lost. That is a different fault from failing to light and it points somewhere else.Related: ignition and gas supply
- EA 227Stop — call an engineerThe boiler tried to light and never detected a flame, so it has shut the gas off and locked out. This is the most common Worcester fault code.Related: ignition and gas supply
- E01Get it checkedThe appliance tried to light and could not confirm a flame, so it has locked out. In winter a frozen condensate pipe is the most likely reason.Related: ignition and gas supply
- F.28Stop — call an engineerThe boiler tried to light and failed three times in a row, so it has shut the gas off and locked out. Do not keep resetting it.Related: ignition and gas supply
- 501Get it checkedNo flame was detected during ignition and the appliance has locked out. Check the gas supply and the condensate pipe before booking anyone.Related: ignition and gas supply
- A01Get it checkedThe burner failed to light and the appliance has locked out. Check the gas supply and, in cold weather, the condensate pipe before calling anyone.Related: ignition and gas supply
Related guides
Common questions about Potterton E133
I am a tenant. Can I thaw the condensate pipe myself?
Yes. The condensate pipe is outside the appliance and pouring warm water on it involves no gas work at all, so it is entirely safe for you to do. Anything requiring the boiler casing to come off is gas work and your landlord must arrange a Gas Safe engineer.
It keeps freezing every winter. Is that just how it is?
No, and it is worth pushing back on. A condensate pipe that freezes annually is either undersized, poorly fallen, or unlagged, and all three are correctable. Building regulations guidance has tightened considerably since most Promax appliances were installed.
How many times can I reset it?
Twice. If two resets have not held, the fault is real. Repeated resetting just cycles gas into a chamber that is not lighting it, and Baxi group appliances will eventually latch out and require a power cycle anyway.
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
- Trade body guidance
- Interviews with working engineers
Checked by Technical reviewer (Gas Safe registration to be displayed on appointment) on 5 August 2026.