An E133 on your Baxi boiler means it tried to fire up but never detected ignition. Here's what's safe to check yourself, and when it becomes a job for a Gas Safe registered engineer.
The E133 fault code is one of the most common errors on Baxi combi, system and heat-only boilers. It is an ignition lockout: the boiler asked for heat, went through its start-up sequence, but the flame-sensing electrode never confirmed that a flame had lit. In plain terms, the boiler thinks it has no gas to burn — so it shuts down safely and locks out rather than keep trying.
Because the most common single cause is a problem with the gas reaching the burner, E133 is usually described as a gas supply or ignition fault. It does not always mean your boiler is broken. Sometimes the gas supply itself has been interrupted, and once that's restored a simple reset clears the code.
Older Baxi models show different codes for the same fault. On some Baxi Duo-tec, EcoBlue and Platinum boilers a gas/ignition lockout may appear as E133, while others use E28 or a flashing flame symbol. Check the fault on your boiler's display against the user manual for your exact model.
None of the steps below involve opening the boiler or touching anything gas-related inside it. If a check doesn't clear the fault, stop and book an engineer.
Because E133 is so often a gas-supply problem, start here:
If you smell gas at any point, do not touch any switches. Leave the property, open doors and windows, and call the National Gas Emergency line on 0800 111 999.
In cold weather, the external plastic condensate pipe (the white or grey pipe running outside to a drain) can freeze and block, which can stop the boiler and trigger a lockout. This is one of the few internal-ish issues you can safely tackle: thaw the outside section of pipe by pouring warm — not boiling — water over it, or holding a wrapped hot-water bottle against it. Never attempt to thaw or open any pipework inside the boiler casing.
If your gas supply is fine and there's no frozen pipe, press and hold the reset button on the front of the boiler for a few seconds (check your manual for the exact button). Give it a couple of minutes to attempt ignition again. If it fires up and stays running, the lockout was a one-off and you're done.
Only reset once. If the boiler locks out on E133 again straight away, do not keep resetting it. Repeated resets won't fix an underlying fault, and forcing a boiler that can't light is unsafe. The next step is a Gas Safe registered engineer.
If the E133 keeps coming back after you've confirmed the gas is on and reset once, the fault is inside the boiler's sealed combustion and gas circuit. This is gas work and must only be done by a Gas Safe registered engineer. You can check any engineer's credentials on the Gas Safe Register.
The kinds of things an engineer will investigate include:
These are not DIY repairs. Removing the casing or touching the gas valve, electrodes, flue or sealed circuit yourself is dangerous and illegal for an unregistered person.
If the fix turns out to be a component replacement, the cost depends on the part. As a rough 2026 guide for an out-of-warranty boiler:
| Typical job | Indicative cost |
|---|---|
| Engineer call-out / diagnosis | £70–£120 |
| Replace ignition / flame electrode | £100–£200 |
| Replace gas valve | £250–£450 |
| Clear / replace condensate trap | £90–£180 |
Figures are indicative and vary by region, model and parts availability. This is exactly the kind of unexpected bill that boiler cover is designed to absorb: most policies include parts, labour and an annual service for a fixed monthly price, so a gas valve failure doesn't land as a one-off lump sum.
Compare boiler cover plans from a selected panel of UK providers and see what's included before your next breakdown.
Compare boiler coverA single E133 caused by a frozen pipe or a topped-up prepayment meter costs you nothing. But when the cause is a failed gas valve or worn electrodes, you're looking at a repair that can run into the hundreds — and ignition components tend to fail on older boilers, often in winter when engineers are busiest. If you'd rather pay a predictable monthly amount than risk a surprise bill, it's worth weighing up whether boiler cover is worth it for your situation. You can also browse the best boiler cover options or cheaper entry-level plans if you want basic protection.
You can safely check your gas supply is on, top up a prepayment meter, thaw an external condensate pipe and press the reset button once. If the fault returns, it's internal gas or ignition work that legally requires a Gas Safe registered engineer.
If your gas is confirmed on and the code still returns after one reset, the boiler is failing to detect a flame for an internal reason — commonly a faulty gas valve, worn ignition or flame electrodes, a flue issue or low gas pressure. These need an engineer to diagnose.
No. Reset once. Repeatedly resetting a boiler that can't ignite won't fix the underlying fault and can be unsafe. If it locks out again, switch off the heating demand and book an engineer.
Not necessarily. Many E133 lockouts are caused by a temporary gas-supply interruption or a single component that can be replaced. An engineer's diagnosis will tell you whether it's a cheap part or a sign the boiler is near end of life.
Most boiler cover policies include parts and labour for breakdowns like an ignition or gas valve fault, plus an annual service. Always check the policy's exclusions, excess and any limits before you buy, and remember a selected panel doesn't cover the whole market.
This article is general information, not advice. It reflects a selected panel of providers, not the whole market. Always have gas faults inspected by a Gas Safe registered engineer.