Baxi E133 Fault Code: Causes, Fixes & Repair Costs
What does the Baxi E133 fault code mean?
E133 on a Baxi boiler is a gas supply or ignition lockout: the boiler tried to light its burner, could not prove a flame within its ignition window, and shut down for safety. It is by far the most common Baxi fault code — and the same code, with the same meaning, appears on Potterton and Main boilers (which share Baxi's control platform), where it is sometimes displayed as 'E1' alternating with '33'. Nine times out of ten in winter the cause is outside the boiler altogether: a frozen condensate pipe, or a gas supply that has stopped (empty prepayment meter, a tripped gas meter valve, or a supply interruption). The homeowner checks take five minutes and often fix it; if E133 comes straight back after one reset, it needs a Gas Safe registered engineer.
General guidance only — not a substitute for professional advice, and not certified by a Gas Safe engineer. Always have your specific appliance assessed by a qualified professional. 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
- No gas reaching the boiler Common
The single most common E133 cause, and the cheapest. Prepayment meters run out of credit (or the emergency credit), the meter's emergency control valve gets knocked closed, a smart meter cuts supply after a missed top-up, or the gas network has a local interruption. Check whether your hob or gas fire lights — if not, it is the supply, not the boiler.
- Frozen condensate pipe Common
In freezing weather the plastic pipe carrying acidic condensate outside freezes solid, the condensate backs up inside the boiler, and the pressure switch or siphon stops the burner lighting — E133 is the result. Classic signs: cold snap, a gurgling noise before lockout, and an external white pipe with ice at the end. Thawing it is a safe homeowner job (see the steps).
- Worn or contaminated ignition electrode Common
The spark electrode erodes and its ceramic insulator cracks or gets coated with deposits; the spark weakens until it can no longer light the gas reliably, especially on cold starts. Usually the first internal component an engineer checks, and one of the cheapest to replace.
- Low gas pressure or undersized supply Sometimes
The boiler receives gas but not enough of it — a partially closed gas cock, a regulator problem at the meter, or a long/undersized gas run that starves the boiler when other appliances run. It lights intermittently, or lights then fails, and locks out on E133 after repeated attempts.
- Flue blockage or air-pressure fault Sometimes
A blocked or damaged flue, a nest in the terminal, or a failing air-pressure switch stops the boiler proving safe combustion airflow, so it refuses to ignite. Often accompanied by fan-related codes (E160) but can present as E133 alone.
- Faulty gas valve or PCB Rare
The gas valve's solenoid or the control board's ignition/flame-sensing circuit fails, so the boiler either never opens the valve or never sees the flame it has lit. This is the expensive end of the E133 spectrum and is diagnosed after everything cheaper has been ruled out.
How to fix it
- Check the gas supply first DIY safe
Try the hob or another gas appliance. If nothing lights, the problem is the supply: check a prepayment meter's credit, make sure the emergency control valve by the meter is fully open (handle in line with the pipe), and if the whole street is out, call the National Gas emergency line on 0800 111 999 to report it. If you smell gas at any point, leave the property and call that number before anything else.
- Check the condensate pipe for ice DIY safe
Find the white or grey plastic pipe (usually 22mm) running from the boiler to an outside drain. In freezing weather, pour warm — never boiling — water along the exposed section, or hold a hot-water bottle against it, until you hear a trickle. Then reset. If this fixes it, the pipe needs lagging or re-routing before the next cold snap; an engineer can also fit a trace-heating kit.
- Reset the boiler once DIY safe
Press and hold the reset button (or turn the selector to the reset position on older Duo-tec/Platinum fascias) for a few seconds. The boiler will run through its ignition sequence — you should hear the fan, a series of clicks, then the burner. One reset after the checks above is sensible. If E133 returns immediately, stop: each further reset is another failed gas admission, and the fault needs diagnosing.
- Note exactly what happens during the attempt DIY safe
Does the boiler click and fail to light at all (spark/gas valve/gas supply), or light briefly and go out (flame sensing, gas pressure, flue)? Does it happen only on cold mornings (condensate) or at any time? These observations are genuinely useful to the engineer and can shorten the visit.
- Call a Gas Safe registered engineer Gas Safe engineer
The engineer will check the working gas pressure at the boiler, inspect and test the ignition electrode and lead, check the flame-sensing circuit, verify the flue and air-pressure switch, and only then look at the gas valve and PCB. Never remove the boiler casing yourself — all work on the gas side is Gas Safe registered work by law.
E133 vs 'E1 33' — same code, two ways of displaying it
Older Baxi, Potterton and Main boilers have a two-character display, so they show a three-digit code in two halves: the screen alternates between E1 and 33. That is why so many people search for 'E1 33' — it is exactly the same fault as E133 on the newer full displays, and everything on this page applies. The same applies to E1 19 (E119, low pressure) and E1 10 (E110, overheat).
On the current Baxi 800 and 600 ranges, which use a newer two-part format (for example E.02-.07), the ignition-failure family is reported differently — if your boiler shows a dotted two-part code, use the Baxi code list to find it.
E133 in cold weather: the condensate pipe, explained
Every condensing boiler produces a steady trickle of acidic water that drains through a plastic pipe. When that pipe runs outside — very common on installations where the boiler is on an external wall — a hard frost freezes it, the water backs up into the boiler's siphon, and the boiler's safety logic stops the burner lighting. On Baxi-platform boilers that presents as E133, occasionally as E28 or E168.
The tell-tale pattern is a boiler that worked yesterday, locked out overnight during a cold snap, and gurgles or bubbles before it fails. Thawing the pipe with warm water and resetting fixes it immediately. The permanent fix is to lag the pipe, increase its fall, shorten its external run, or fit a trace-heating cable — a small job that prevents the most common winter breakdown in the country.
E133 on Potterton and Main boilers
Potterton (Promax, Gold, Titanium, Assure) and Main (Eco Compact, Eco Elite) boilers are built on the same Baxi Heating platform and use the identical E133 code with the identical meaning. The homeowner checks and the engineer diagnosis on this page apply to them too. If you own one of those brands, the dedicated pages are here: Potterton E133, Main E133, and you can compare E133 across every brand.
What the engineer will check, in order
A methodical E133 diagnosis runs cheapest-first. First the gas: is there a supply, and is the working pressure at the boiler's test point within specification under load? Second the ignition: the electrode gap, the condition of the ceramic and lead, and whether a healthy spark is present. Third, flame detection: the ionisation signal once the burner lights (a boiler that lights then drops out on E133 is usually here). Fourth the airflow: flue integrity, terminal, and air-pressure switch. Only then the gas valve and PCB.
A good engineer will also carry out a combustion check with a flue-gas analyser after any ignition repair, because a boiler that has been struggling to light may have been running with poor combustion for weeks.
Parts you may need
- Ignition electrode · from £20
- Ignition lead · from £15
- Gas valve · from £120
- Condensate pipe lagging / trace heater · from £15
- Control PCB · from £180
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 £0–£450, depending on the underlying cause.
Frequently asked questions
What does E133 mean on a Baxi boiler?
E133 is a gas supply or ignition lockout: the boiler tried to light, could not detect a flame, and shut down. The most common causes are no gas reaching the boiler (empty prepayment meter, closed valve, supply outage) and a frozen condensate pipe in cold weather. Check those, reset once, and call a Gas Safe engineer if it returns.
Is E1 33 the same as E133?
Yes. Boilers with a two-character display show E133 as 'E1' alternating with '33'. It is exactly the same ignition/gas-supply fault, and the same checks and fixes apply.
Can I fix a Baxi E133 fault myself?
Often, yes — if the cause is the gas supply (top up the meter, open the emergency control valve) or a frozen condensate pipe (thaw with warm water), you can resolve it and reset the boiler yourself. Anything inside the boiler — electrode, gas valve, PCB, flue — must be done by a Gas Safe registered engineer.
Why does my Baxi show E133 every cold morning?
That pattern is the frozen condensate pipe almost every time. The pipe freezes overnight, the boiler locks out, and it clears once the day warms up or you thaw it. Lagging or re-routing the pipe, or fitting a trace heater, stops it recurring.
How many times can I reset a Baxi E133?
Reset once after checking the gas supply and condensate pipe. If E133 comes back straight away, stop — each reset is another attempt to admit and ignite gas against a fault that has not gone away, and repeated attempts can flood the combustion chamber and make things worse.
How much does an E133 repair cost?
Anywhere from nothing (a meter top-up or thawed pipe) to roughly £80–£150 for a call-out and new ignition electrode, up to £300–£450 if the gas valve or PCB has failed. Prices vary by region and by whether it is an emergency call-out; get a written quote.
Does E133 mean my boiler is dangerous?
The lockout itself is the safety system working — the boiler has stopped because it could not prove a flame, which is exactly what it should do. What you must never ignore is a smell of gas: if you can smell gas, leave the property and call 0800 111 999.
My Potterton / Main boiler shows E133 — is it the same fault?
Yes. Potterton and Main boilers share Baxi's control platform, so E133 has the same meaning and the same fixes. See the Potterton E133 and Main E133 pages, or the cross-brand E133 comparison.