Baxi E0 Fault Code: Causes, Fixes & Repair Costs
What does the Baxi E0 fault code mean?
The E0 code on a Baxi boiler indicates that the control board has detected a problem with one or more of the boiler's temperature sensors (NTC thermistors). These sensors continuously monitor water temperature at key points — typically the flow, return, and domestic hot water circuits — allowing the boiler to regulate output and trigger safety cutoffs. When the control board receives a reading that falls outside expected parameters, or no signal at all, it raises the E0 fault and locks the boiler out to prevent unsafe operation. Note: on newer Baxi models, this general sensor fault has been split into more specific codes — E20 (flow sensor), E28 (flue sensor), E40 (return sensor), and E50 (DHW sensor) — so if your display shows one of those, cross-reference your model accordingly. On older models that only display E0, any of those sensor circuits could be the source of the problem.
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.
Common causes
- Faulty or failed NTC thermistor Common
The NTC thermistor itself has degraded, burned out, or gone open-circuit. An open-circuit sensor produces infinite resistance, which the control board immediately flags as a fault and triggers lockout. This is the single most frequent cause of the E0 code.
- Loose or disconnected wiring to the sensor Common
The wiring harness connecting the NTC sensor to the PCB can work loose over time due to vibration, thermal cycling, or poor original fitment. Even a partially disconnected plug can cause intermittent or permanent signal loss, producing the E0 code without the sensor itself being damaged.
- Corroded or damaged sensor connections Sometimes
Moisture ingress or general ageing inside the boiler casing can cause corrosion to build up at the sensor connector pins. Corroded contacts increase electrical resistance in the circuit, sending a distorted signal to the control board that may be interpreted as a sensor fault.
- Sensor resistance drift over time Sometimes
NTC sensors that have been in service for several years can gradually drift away from their original resistance-temperature curve. The sensor remains functional but consistently reports inaccurate temperatures, causing the boiler to behave erratically or eventually lock out on E0. This is harder to diagnose than an outright failure.
- PCB fault Rare
If the control board's input circuitry for a sensor channel has failed, the board will log an E0 fault even when the sensor and wiring are both in good condition. PCB faults are relatively uncommon as a root cause but must be considered if sensor and wiring checks prove negative.
How to fix it
- Reset the boiler once or twice DIY safe
Locate the reset button on your Baxi's front panel (usually marked with a flame or reset symbol) and press and hold it for 3–5 seconds until the boiler attempts to restart. Wait a full minute for it to complete the startup sequence. If the boiler runs normally afterwards, monitor it closely over the next 24 hours. If E0 returns within a short time, the fault is genuine and a reset alone will not cure it — avoid resetting more than two or three times in total, as repeated lockouts without a fix can mask a worsening problem.
- Check your gas supply is on DIY safe
Confirm that the gas isolation valve on the supply pipe to the boiler is fully open (handle in line with the pipe). Check that other gas appliances in the property, such as a hob or fire, are working normally. If you have no gas supply at all, contact your gas supplier before going any further.
- Inspect sensor wiring and connections — engineer task Gas Safe engineer
A Gas Safe registered engineer will remove the boiler casing and visually inspect the wiring harnesses running to each NTC thermistor. They will check for loose plugs, chafed or broken cables, and signs of corrosion or heat damage at the connector pins. Reseating a loose connector sometimes resolves the fault immediately without any parts being needed.
- Test the NTC sensor with a multimeter — engineer task Gas Safe engineer
The engineer will measure the sensor's resistance at a known water temperature and compare the reading against the manufacturer's resistance-temperature table. A sensor reading open-circuit, short-circuit, or significantly outside the expected range will be confirmed as faulty and earmarked for replacement.
- Replace the faulty NTC thermistor — engineer task Gas Safe engineer
Genuine Baxi NTC sensors are widely available and relatively inexpensive as parts (typically £8–£30 depending on the specific sensor). The engineer will drain the relevant circuit if necessary, fit the new sensor, refill and repressurise the system, and run the boiler through a full heat cycle to confirm the fault has cleared. If your boiler is still within its Baxi warranty period, insist on a genuine Baxi part to protect your cover.
- Investigate PCB if the fault persists after sensor replacement — engineer task Gas Safe engineer
Should E0 return even after a confirmed sensor replacement and wiring checks, the engineer will assess the PCB's sensor input channels. PCB diagnosis may involve swapping in a known-good board or bench-testing the existing one. Replacement is a more significant repair — see the FAQ below for typical costs.
- Contact a Gas Safe registered engineer DIY safe
If the boiler has not cleared after a reset or two, book a Gas Safe registered engineer to carry out a full diagnostic. You can verify an engineer's registration at the Gas Safe Register website (gassaferegister.co.uk). Have your boiler model number and any recent service history to hand — it will speed up the visit.
Parts you may need
- Baxi NTC flow temperature thermistor · from £18
- Baxi NTC return temperature thermistor · from £18
- Baxi DHW NTC thermistor · from £22
- Sensor wiring harness · from £35
- Baxi PCB (control board) · from £220
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 £90–£250, depending on the underlying cause.
Frequently asked questions
Can I fix the Baxi E0 fault myself?
The only DIY steps that are safe are resetting the boiler (up to two or three times) and confirming your gas supply is on. All internal work — inspecting wiring, testing sensors, and replacing components — must be carried out by a Gas Safe registered engineer. Opening the boiler casing yourself without Gas Safe registration is both illegal under UK gas safety regulations and potentially dangerous.
How much does it typically cost to fix a Baxi E0 fault in the UK?
For the most common repair — replacing an NTC thermistor including engineer call-out and labour — most homeowners pay somewhere between £90 and £250. The sensor part itself is inexpensive (£8–£30), so the bulk of the bill is labour. If the PCB turns out to be at fault, costs rise considerably; PCB replacement on a Baxi boiler typically runs £250–£450 including parts and labour. That said, PCB faults are an uncommon cause of E0, so most people do not face that level of expenditure.
My Baxi boiler shows E0 intermittently but then clears on its own — is that serious?
Intermittent faults that self-clear often point to a loose wiring connection or a sensor that is beginning to drift rather than one that has completely failed. While it can be tempting to ignore the fault if the boiler keeps recovering, intermittent faults tend to worsen over time. It is worth booking an engineer to inspect the sensor circuit before the boiler progresses to a permanent lockout — ideally before the colder months when you need reliable heating most.
Will fitting a pattern (non-genuine) NTC sensor affect my Baxi warranty?
If your boiler is under two years old or still within a Baxi extended warranty period, fitting a non-genuine (pattern) part risks invalidating the remaining warranty. Baxi's warranty terms require genuine parts fitted by a registered installer to keep cover intact. Pattern sensors do work, and reputable ones perform comparably in testing, but they typically carry only a 90-day warranty versus 12 months on genuine Baxi parts. On an out-of-warranty boiler the choice is yours, but on a newer boiler it is generally worth paying for the genuine part.