Baxi 200 and 400 series fault codes
Look up what your Baxi's display is telling you, find the part most likely at fault, and see whether the fix is one you can do yourself or one for a Gas Safe registered engineer.
Which Baxi model do you actually have?
Baxi has sold the 200, 400, 600 and 800 ranges alongside each other for years, and the casings can look near-identical from across the kitchen. The badge on the front fascia usually tells you the range, but not always the generation within it, and that gap is where the wrong part gets ordered.
Why the exact model matters
A fault code that means one thing on a Baxi 200 can point to a different component on a Baxi 400, even though the display and the wording look the same. Boilers within the same range have also been updated over time, with the control board, the gas valve or the sensor changed between production runs while the outer casing stayed put. The part number and the fault code table that apply to your boiler depend on which version you actually have in front of you.
Where to find the details you need
The rating plate carries the information that settles the question. It's usually fixed inside the casing, behind the front panel or lower access door.
- The full model name as printed by Baxi
- The serial number, which usually encodes the build date and helps place your boiler within a generation
- The GC number, if you need to cross-check the model against manufacturer documentation
Have this information to hand before you order a part or look up a fault code. A part that fits a Baxi 400 from one production run will not always fit a Baxi 400 from another, and a supplier working from the range name alone is guessing.
When the model is genuinely unclear
If the rating plate is missing, worn away, or was replaced during an earlier repair, a Gas Safe registered engineer working on the boiler will be able to confirm the model from the boiler's internal layout and components during a service visit. Ordering a part against a guessed model risks a mismatch on connectors or fittings that only becomes obvious once the casing is open.
Baxi 200 and 400 fault codes grouped by likely cause
Baxi's 200 and 400 series share a numbering pattern, but the exact code, the part it points to and the firmware it applies to can shift between model years. Use the groupings below to work out which system is likely at fault, then check the precise code against your boiler's rating plate before ordering anything.
| Fault type | Likely component | Gas Safe requirement |
|---|---|---|
| Ignition lockoutThe boiler tries to light and fails, then locks out after repeated attempts. Worth checking gas supply and electrode condition before assuming a PCB fault. | Gas valve, ignition electrode, or PCB | Gas Safe registered engineer required |
| No flame detectedDifferent from a lockout code in that the boiler may attempt ignition repeatedly without ever confirming flame. Flue condition is worth ruling out early. | Ignition electrode, gas valve, or blocked flue | Gas Safe registered engineer required |
| Low or high system pressureShows on the display as a pressure warning. Check the filling loop and pressure gauge reading before ordering a replacement part. | Pressure relief valve (PRV), expansion vessel, or pressure sensor | Repressurising is usually DIY-permissible; replacing the valve or vessel may need a qualified engineer |
| Fan or air pressure faultOften triggered by a blocked flue terminal or a failing fan. Worth checking the outside terminal first. | Fan, air pressure switch, or flue obstruction | Gas Safe registered engineer required where the flue is involved |
| Sensor or thermistor faultShows as an erratic or fixed temperature reading on some models. Confirm which sensor the code refers to before ordering. | NTC thermistor (flow or return) | DIY-permissible on many models, but check the manufacturer guidance for your specific range |
| PCB or electronics faultA catch-all category for codes that don't point to a mechanical part. Worth ruling out simpler causes first, since a PCB is one of the costlier replacements. | Printed circuit board (PCB) | Gas Safe registered engineer required if the fault affects gas-carrying components |
These are common fault categories for the Baxi 200 and 400 series, not a full code-by-code list. The exact code, the OEM part number, and whether Gas Safe registration applies all depend on the model range and firmware version printed on the boiler's rating plate.
Baxi 200 and 400 E133: ignition lockout diagnostic sequence
What E133 means
E133 appears when the boiler has attempted ignition and failed to detect a flame within its allowed number of tries, so the control board locks the boiler out. Ignition on the 200 and 400 series depends on several parts acting together: gas supply, the ignition electrode, the gas valve, and the printed circuit board (PCB) that reads the flame signal back.
Likely causes
The most common cause is a fouled or misaligned ignition electrode, followed by a gas valve that isn't opening fully and a PCB no longer reading the flame signal correctly. Low gas pressure at the appliance and a partially blocked flue can also stop ignition completing, particularly after recent work on the gas supply or flue run.
- Electrode: soot build-up or an electrode sitting too far from the burner to spark reliably
- Gas valve: not opening fully, or not holding open long enough for a flame to establish
- PCB: ignition is happening but the flame signal isn't being registered
- Gas supply: pressure at the appliance below what the burner needs
- Flue: a partial blockage disturbing the burn
Diagnostic sequence
- Reset the boiler once and watch the ignition attempt if a viewing window is fitted.
- Note any other fault codes appearing alongside E133, such as a low pressure or flame loss code, before resetting again.
- Isolate the electrical supply to the boiler before removing any panel.
- Inspect the ignition electrode for soot and confirm its position against the burner.
- Check gas supply pressure at the appliance against the boiler's data plate.
Isolating the electrical supply carries its own risk if you're not used to working around mains wiring, and a qualified electrician is the right person to call if you're unsure.
When to stop and call an engineer
Checking or adjusting the ignition electrode, gas valve or gas supply pressure is gas work. This work must be carried out by a Gas Safe registered engineer.
Before ordering a replacement gas valve or PCB, check the part number on the label of the failed component against your boiler's model and serial range, since the correct part can differ between firmware versions even within the 200 and 400 series.
Common questions about Baxi 200 and 400 faults
Can I reset my Baxi 200 or 400 boiler myself after a fault code appears?
Most Baxi 200 and 400 series boilers reset with the button on the front panel, and a single reset is normally safe to try once. If the fault code returns straight after resetting, that points to a real component failure, and repeated resetting without diagnosing the cause can mask a gas or electrical fault. Where the code relates to ignition, flame loss, or a gas valve, stop resetting and get the underlying cause checked.
Why does the same fault code keep coming back after I reset the boiler?
A fault code that returns after every reset usually means the component behind it is still failing. Boilers are built to lock out again as soon as the same condition is detected, so a repeat code is the boiler telling you the part needs attention. Checking the fault against the specific code is the next step, since the likely component differs by code and by whether you have a 200 or 400 series model.
Are Baxi 200 and 400 series fault codes the same, or do they differ by model?
The 200 and 400 series share some fault logic but not all of it, and part numbers in particular can differ between the two ranges and between model years within each range. A code that means a failed pressure sensor on one model can point to a different component on another, which is why checking the fault code against your specific model and, where shown, the serial or firmware range matters before ordering a part.
Can I fit a replacement part on my Baxi boiler myself?
Whether you can fit a part yourself depends entirely on what the part is and what it connects to. Components that only touch the water side of the system, such as a pump or an expansion vessel in some cases, are more often DIY-permissible, while anything connecting to the gas valve, burner, or flue is not. This work must be carried out by a Gas Safe registered engineer wherever the component is gas-carrying, and that applies regardless of how confident you feel fitting it.
How do I know which part number to order for my boiler?
The part number depends on the exact model range and, for some components, the serial or firmware range of your particular boiler. The same failure mode can call for a different OEM part across model years, so checking the label on your existing component against the part reference before ordering avoids fitting something that looks right but does not connect properly.
What should I do if I'm not sure whether a repair needs a Gas Safe registered engineer?
If the component you are replacing connects to the gas supply, the burner, the flue, or the gas valve assembly, the work needs a Gas Safe registered engineer regardless of how the fault code is described elsewhere. Where a component sits only on the water or electrical side, such as a circulating pump, restrictions can differ, but electrical isolation still carries its own risk and should be treated with the same care as any mains-connected work.
Is it worth calling an engineer even if I've identified the faulty part myself?
Identifying the likely component narrows down what a fault code means, but it does not replace a physical check of the boiler. A part that looks like the obvious cause from the fault code can turn out to be a symptom of something else, such as a wiring fault feeding a false reading to a sensor, and an engineer working on the appliance directly can confirm that before a part is bought and fitted unnecessarily.
Find a verified supplier for your Baxi 200 or 400 series part
Once you know the part number you need, the supplier directory shows who stocks it, filtered by dispatch speed and returns policy, with each listing carrying the date it was last checked.