Baxi E163 Fault Code: Causes, Fixes & Repair Costs
What does the Baxi E163 fault code mean?
The E163 code appears on Baxi boilers when the domestic hot water (DHW) NTC thermistor sensor develops a fault. The boiler's PCB uses this small temperature-sensing probe to monitor hot water temperature — its electrical resistance changes predictably as the water warms up, letting the board calculate an accurate reading. E163 covers two distinct failure states: a short circuit (s.c.), where the sensor's circuit collapses and sends a zero-resistance signal, and an open circuit (o.c.), where the circuit is broken entirely and no signal reaches the PCB. In either case, the boiler cannot safely regulate domestic hot water and locks out to protect itself. Central heating may continue to work, but hot water from taps and showers will be unavailable until the fault is resolved.
General guidance only — not a substitute for professional advice, and not certified by a Gas Safe engineer. Always have your specific appliance assessed by a qualified professional. 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
- Failed or degraded DHW NTC sensor Common
The sensor itself has worn out or failed internally — a very common occurrence on boilers over eight to ten years old. The thermistor element inside the sensor degrades over time, causing it to produce wildly inaccurate resistance readings or no reading at all. This results in either a short or open circuit condition and triggers E163. Replacing the sensor (Baxi part 5114725 is widely used across the range) is usually all that is needed.
- Loose, corroded, or damaged wiring connections Common
The wiring harness connecting the DHW NTC sensor to the PCB can suffer from loose plug connections, corrosion at the terminals, or physical damage to the cable insulation. Any of these interrupts the signal between sensor and board and can mimic a genuine sensor failure. An engineer will check the plug, terminals, and cable run before condemning the sensor itself.
- Faulty PCB Rare
In a minority of cases the sensor and its wiring test fine, pointing the finger at the PCB rather than the sensor. A failing PCB can misinterpret incoming sensor data or lose the ability to read that particular input channel altogether, generating a false E163. PCB replacement is a more involved and costly repair but becomes the diagnosis once sensor and wiring have been ruled out.
How to fix it
- Check that your gas supply is working DIY safe
Before assuming the boiler is at fault, quickly confirm your gas supply is live — check that a gas hob or other gas appliance lights normally. If there is no gas reaching the property, contact your gas supplier rather than the boiler manufacturer.
- Reset the boiler (up to two or three times) DIY safe
On most Baxi models, press and hold the reset button on the front panel for approximately one to three seconds until the boiler restarts. A brief electrical glitch can occasionally trip E163 without a genuine component fault, and a single reset may clear it. If the code returns after one or two resets, further resets are unlikely to help and you should move to the next step.
- Check system pressure DIY safe
While this fault is sensor-specific, it is worth glancing at the pressure gauge on the front of the boiler. Correct operating pressure is typically between 1 and 1.5 bar when the system is cold. If it has dropped below 1 bar, top it up via the filling loop and reset. Low pressure is not a direct cause of E163 but can accompany other issues.
- Have a Gas Safe engineer inspect the DHW NTC sensor wiring and connections Gas Safe engineer
A registered engineer will remove the boiler casing and trace the wiring harness from the DHW NTC sensor back to the PCB. They will check for loose plugs, corroded terminals, and any visible damage to the cable insulation. This inspection takes only a few minutes and often reveals the fault without needing a new part.
- Have the engineer test the sensor's resistance with a multimeter Gas Safe engineer
The engineer will measure the sensor's resistance at a known water temperature and compare the reading against the manufacturer's specification. A reading that is far too low (short circuit) or infinite (open circuit) confirms the sensor has failed and needs replacing.
- Replace the DHW NTC sensor if confirmed faulty Gas Safe engineer
The Baxi DHW NTC sensor is a relatively affordable part (Baxi part 5114725 fits a wide range of models) and straightforward to swap out for a qualified engineer. Once replaced, the boiler is reset and function-tested to confirm the fault has cleared and hot water is being regulated correctly.
- Have the PCB inspected or replaced if the fault persists after sensor replacement Gas Safe engineer
If a brand-new sensor and verified wiring still produce E163, the PCB is the next suspect. The engineer will carry out further electrical diagnostics to confirm PCB failure before recommending replacement, as a new PCB is a significantly more expensive repair.
- Call a Gas Safe registered engineer if you have not already done so Gas Safe engineer
All work beyond the basic homeowner checks above must be carried out by a Gas Safe registered engineer. You can find one at gassaferegister.co.uk. Always ask to see their Gas Safe ID card before any work begins.
Parts you may need
- Baxi DHW NTC Thermistor Sensor (part 5114725) · from £25
- Wiring harness / sensor loom · from £35
- Baxi PCB (model-dependent) · from £180
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 £100–£250, depending on the underlying cause.
Frequently asked questions
Will my central heating still work if E163 is showing?
In most cases, yes. E163 is specifically a domestic hot water sensor fault, so the boiler may continue to provide central heating while locking out the hot water circuit. However, some Baxi models will lock out all functions as a precaution, so your experience may vary. Either way, the fault needs fixing before you can rely on the boiler fully.
Can I fix the E163 fault myself?
You can safely try a boiler reset (once or twice) and check that your gas supply is working, but that is as far as a homeowner should go. Replacing the NTC sensor or inspecting the wiring inside the boiler casing must be done by a Gas Safe registered engineer. Attempting it yourself risks personal injury, could invalidate your boiler warranty, and is a legal requirement for gas appliance work in the UK.
How much should I expect to pay to fix E163?
For the typical repair — sensor replacement including callout, parts, labour, and VAT — most UK homeowners pay in the region of £100 to £250 on a standard weekday. The DHW NTC sensor itself is an affordable part (around £20–£30) and the job is not particularly labour-intensive. If the PCB turns out to be the underlying cause, costs can rise significantly — a replacement PCB can add £200–£400 or more to the bill — but that is an uncommon outcome for this fault code.
How do I know whether E163 is a short circuit or open circuit fault on my Baxi?
The E163 code covers both conditions, and Baxi's boiler display typically shows just 'E163' without distinguishing between the two. The difference — short circuit versus open circuit — is determined by the engineer when they test the sensor's resistance with a multimeter. A near-zero resistance reading points to a short circuit; an infinite or no-reading result indicates an open circuit. In practice, the fix (inspect wiring, test and replace the sensor if faulty) is the same either way.