Potterton E133 Fault Code: Ignition Failure & Safety Lockout
The E133 code appears on Potterton boilers — often displayed as 'E1' alternating with '33' — when the boiler has attempted to ignite, failed to detect a stable flame, and shut itself down as a safety precaution. In plain terms, the boiler tried to light, couldn't confirm a flame was present, and locked out rather than continue operating unsafely. This code is also common on Baxi and Main boilers, which share closely related ignition and gas control systems.
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.
What does the Potterton E133 fault code mean?
The E133 code appears on Potterton boilers — often displayed as 'E1' alternating with '33' — when the boiler has attempted to ignite, failed to detect a stable flame, and shut itself down as a safety precaution. In plain terms, the boiler tried to light, couldn't confirm a flame was present, and locked out rather than continue operating unsafely. This code is also common on Baxi and Main boilers, which share closely related ignition and gas control systems.
Common causes
- Frozen condensate pipe Common
In cold weather the condensate pipe — which carries acidic waste water from the boiler to an outside drain — can freeze solid. The resulting blockage triggers a safety shutdown and is one of the most frequent winter causes of E133. If temperatures have recently dropped below 0°C, this should be your first suspicion.
- Interrupted or insufficient gas supply Common
If the gas supply to the boiler is restricted or completely absent, no flame can form. This might be because the gas isolation valve has been accidentally turned off, there is a wider supply interruption in your area, or — if you have a prepayment meter — you have run out of credit.
- Worn or misaligned ignition electrodes Sometimes
The ignition electrode creates the spark that lights the burner, while the flame-sensing electrode confirms the flame is present. If either is eroded, cracked, or has shifted out of position, the boiler may spark without successfully detecting a flame, causing repeated lockouts.
- Faulty gas valve Sometimes
The gas valve controls the flow of gas to the burner. If it has become stuck, worn, or is not opening correctly on demand, insufficient gas reaches the burner and ignition fails. This is an internal component that must be diagnosed and replaced by a Gas Safe engineer.
- Blocked or obstructed flue Sometimes
A blocked flue or air intake restricts the combustion air the burner needs to establish a flame. Bird nests, debris, or a damaged terminal can all cause this, particularly on boilers with externally accessible flue outlets.
- Faulty PCB (printed circuit board) Rare
The PCB governs the ignition sequence. If it is sending incorrect signals — or none at all — to the ignition or gas valve, the boiler will fail to light even when all other components are in good condition. PCB faults are less common but can be difficult to distinguish from other causes without specialist test equipment.
How to fix it
- Check that other gas appliances in your home are working DIY safe
Try a gas hob burner or another gas appliance. If nothing runs on gas, the problem is with your supply rather than the boiler itself. Contact your gas supplier or National Gas Emergency (0800 111 999) if you suspect a supply fault.
- Check your gas meter credit if you have a prepayment meter DIY safe
A meter that has run out of credit will cut the gas supply completely. Top up and allow a few minutes for the supply to restore before attempting to reset the boiler.
- Check whether a frozen condensate pipe is the culprit DIY safe
If it is cold outside (near or below 0°C), locate the condensate pipe — typically a white or grey plastic pipe (often 21.5 mm or 32 mm diameter) that exits the boiler and runs to an outside drain or soakaway. If it feels solid or you can see ice, it is likely frozen. Pour warm — not boiling — water along the pipe from the outside, working towards the boiler. Boiling water can crack the pipe due to thermal shock. Once thawed, proceed to reset the boiler.
- Check your boiler pressure DIY safe
Look at the pressure gauge on the boiler front. It should sit between 1 and 1.5 bar when the system is cold. If it reads below 1 bar, top it up using the filling loop (refer to your boiler manual for the location). Do not pressurise above 1.5 bar. Consistently low pressure that returns quickly may indicate a leak and warrants an engineer visit.
- Reset the boiler DIY safe
Once you have completed the checks above, press and hold the reset button (usually marked with a flame or 'R' symbol) for around 3 seconds. The boiler should attempt to re-ignite. If it fires up successfully, monitor it over the next hour. If E133 returns, attempt one further reset — but do not reset more than two or three times in total. Repeated reset attempts can accelerate wear on the ignition electrode.
- Call a Gas Safe registered engineer if the fault persists Gas Safe engineer
If E133 returns after resetting, or you were unable to identify an obvious cause such as frozen pipework or a supply interruption, a Gas Safe registered engineer should attend. They will carry out a full ignition system inspection, test the flame-sensing electrode and ignition lead, examine the gas valve operation, check the flue and air intake for blockages, and test PCB outputs. Do not continue resetting the boiler repeatedly while waiting — leave it in lockout.
Parts you may need
- Ignition electrode · from £25
- Flame sensing electrode · from £20
- Ignition lead / HT lead · from £15
- Gas valve · from £120
- PCB (printed circuit board) · from £180
- Condensate pipe insulation lagging · from £8
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 £150–£350, depending on the underlying cause.
Frequently asked questions
Can I fix Potterton E133 myself without calling an engineer?
Some causes of E133 are safe for a homeowner to address — thawing a frozen condensate pipe, checking the gas supply is on, topping up system pressure, and resetting the boiler are all reasonable DIY steps. However, if those checks do not resolve the fault, the cause is almost certainly internal — a faulty electrode, gas valve, or PCB — and all of that work must be carried out by a Gas Safe registered engineer. It is illegal and dangerous for an unqualified person to work on gas components.
Why does my Potterton boiler keep showing E133 after I reset it?
If E133 keeps returning after a reset, the underlying cause has not been fixed. A one-off reset after, say, a temporary gas supply blip is perfectly normal. Repeated lockouts point to a worn ignition electrode, a gas valve that is not opening reliably, or a PCB fault. Continuing to reset the boiler masks the problem and can accelerate wear — book an engineer rather than keep resetting.
How much does it cost to fix a Potterton E133 fault in the UK?
For the most common causes, most people pay somewhere between £150 and £350 including call-out, labour, and any parts. Thawing a frozen condensate pipe yourself costs nothing; having an engineer do it typically adds a call-out fee of £60–£100. Ignition electrode replacement usually comes in at £150–£250 all-in, and a gas valve replacement at around £180–£300. PCB replacement is significantly more expensive — typically £450–£700 in 2025 — and on an older boiler it is worth getting a boiler replacement quote at the same time to compare.
Is E133 the same fault code on Baxi and Main boilers?
Yes. Potterton, Baxi, and Main boilers are all part of the same manufacturing group and share very similar internal components and control systems. The E133 code carries the same meaning across all three brands — an ignition or flame-detection failure leading to a safety lockout — and the diagnostic and repair process is essentially identical.