What the E133 code means
On most current Baxi combis, E133 means an ignition failure or an interruption of the gas supply. When the boiler needs to heat water, it opens the gas valve and sparks the ignition electrode. A flame sensor then confirms that the burner has lit. If no flame is detected, or the flame is lost because gas stops arriving, the boiler makes further attempts. When those fail it locks out and shows E133.
You may also see a flame symbol with a line through it on some models. The code is a safety shutdown. It stops gas flowing when the boiler cannot confirm it is burning safely.
E133 is one of the most common Baxi codes, and in many cases the cause is outside the boiler. A frozen condensate pipe, a switched-off gas valve or a prepayment meter out of credit will all trigger it.
Common causes of E133
| Cause | What you might notice | Who fixes it |
|---|---|---|
| Gas supply off or interrupted | Hob or other gas appliances not working | You (check meter), or the gas network |
| Prepayment meter out of credit | Meter shows no credit or emergency credit used | You |
| Gas isolation valve closed | Handle under the boiler sits across the pipe | You |
| Frozen or blocked condensate pipe | Freezing weather, gurgling from the boiler | You (thaw with warm water) |
| Worn or poorly placed ignition electrode | Repeated clicking, fault getting more frequent | Gas Safe engineer |
| Faulty gas valve | Gas works elsewhere but E133 returns each time | Gas Safe engineer |
| Flue, fan or circuit board problem | Code persists after every other check | Gas Safe engineer |
Why the condensate pipe matters
Baxi combis are condensing boilers, which means they produce acidic water as they run. This drains away through a plastic pipe, often to an outside drain. In freezing weather that pipe can ice up. The water then backs up into the boiler and the burner cannot light or stay lit, which is why E133 appears so often on cold mornings.
When the fault comes and goes
If E133 appears now and then but the boiler works normally after a reset, keep a note of when it happens. A fault that only shows in freezing weather points to the condensate pipe. One that happens at random, or more often as the weeks go by, is more likely to be a worn electrode or a gas valve that is starting to fail.
Safe checks you can do yourself
Work through these in order. Never remove the boiler casing.
- Check other gas appliances. If your hob will not light either, the boiler is not the problem. Check the meter or contact your supplier.
- Check the meter and credit. If you have a prepayment meter, make sure there is credit. After topping up, follow the instructions on the meter to restore the supply.
- Check the gas isolation valve under the boiler. It should be open, with the handle in line with the pipe.
- Look at the condensate pipe. In freezing weather, thaw it with warm (not boiling) water or a hot water bottle. Our frozen condensate pipe guide explains how to find it and thaw it safely.
- Check power and controls. Make sure the fused spur is switched on and the thermostat and timer are asking for heat.
- Reset the boiler. Press the reset button, or press and hold it on some models, as your manual describes. Stop after 2 or 3 attempts.
If you smell gas, do not reset the boiler. Turn off the gas at the meter if it is safe to do so, open doors and windows, and call the National Gas Emergency Service on 0800 111 999. Avoid electrical switches and naked flames. Call the same number if you suspect the gas supply to your area has failed.
When to call a Gas Safe engineer
If gas is reaching your other appliances, the isolation valve is open, the condensate pipe is clear and E133 still comes back after 2 or 3 resets, you need a Gas Safe registered engineer. The cause is then almost certainly inside the boiler.
An engineer will typically measure the gas pressure at the boiler, check the ignition electrode and its gap, test the gas valve, and inspect the fan, flue and condensate trap. These parts carry gas and mains electricity, so they must never be touched by a homeowner.
If your Baxi is still under its manufacturer warranty, contact Baxi first. Warranty work is usually free, and using another engineer may affect the cover.
Typical repair costs in the UK
These are typical ranges only. Prices vary by region, boiler model and whether parts are in stock.
| Repair | Typical cost |
|---|---|
| Engineer call-out and diagnosis | Typically £80 to £150 |
| Ignition electrode replacement | Typically £100 to £180 |
| Gas valve replacement | Typically £250 to £450 |
| Thawing a frozen condensate pipe yourself | Free |
A supply problem or frozen pipe may cost nothing to fix. If the engineer finds more than one worn part, ask for a combined quote, as it usually works out cheaper than separate visits.
How to stop E133 coming back
- Book an annual service. The engineer cleans and checks the electrode, burner and condensate trap. See our guide to what a boiler service includes and costs.
- Protect the condensate pipe. Insulation, rerouting indoors or a wider pipe can all reduce the chance of freezing. Ask your engineer what suits your home.
- Keep the meter topped up, especially in winter when gas use rises.
- Use a low background heat overnight in very cold weather to keep the pipe from freezing.
- Keep an eye on the pressure. A separate code, E119, shows when the pressure is too low.
If E133 only appears on frosty mornings, the condensate pipe is the most likely cause. Tell your engineer, as it can save time on diagnosis.