Worcester Bosch E2 223 Fault Code: Causes, Fixes & Repair Costs
What does the Worcester Bosch E2 223 fault code mean?
The E2 fault code on Worcester Bosch boilers points to a problem with the flow temperature NTC (Negative Temperature Coefficient) sensor — the component that measures the temperature of water leaving the heat exchanger and heading into your central heating circuit. Without accurate readings from this sensor, the boiler cannot control water temperature safely, so it shuts down as a precaution. The sub-code 223 is the open-circuit or disconnection variant of this fault, most commonly seen on newer Worcester Bosch Greenstar 8000-series models, and means the boiler's electronics are receiving no signal from the sensor at all. This is distinct from E2 222, which indicates a short-circuit condition in the same sensor — but both sub-codes point to the same component and are resolved in the same way. If your display shows E2 with no sub-code, or E2 222, the information on this page still applies directly.
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
- Flow NTC sensor open circuit or disconnected wiring Common
The most frequently seen cause on engineer call-outs. The electrical connection between the flow NTC sensor and the PCB has broken down — either the sensor plug has worked loose from vibration over time, or a wire in the sensor harness has become open-circuit. The boiler receives no temperature signal and locks out. Sub-code 223 specifically points to this open-circuit condition.
- Failed or worn flow NTC sensor Common
Over several years of repeated heating cycles, the sensor element itself degrades and eventually stops producing reliable resistance readings. This is more common on boilers over eight years old. The sensor may have worked intermittently for a while before triggering a permanent lockout.
- Short circuit in the sensor or its wiring Sometimes
A short circuit within the sensor body or along its cable causes the PCB to read an impossible temperature value. Worcester Bosch documents this as the E2 222 variant, but on some models the display may show 223 depending on firmware interpretation. Damaged cable insulation — from heat, rodents, or a previous repair — is a typical route cause.
- PCB fault causing false sensor reading Rare
Rarely, the PCB itself misreads or generates a false E2 signal despite the sensor being in good condition. A Gas Safe engineer can confirm this by testing the sensor's resistance values directly and comparing them against specification. PCB failure is an unlikely explanation unless the sensor and wiring test as healthy.
How to fix it
- Check your gas supply is working DIY safe
Before assuming the boiler is faulty, confirm that other gas appliances in your home — a hob or gas fire — are working normally. If there is no gas supply, contact your gas network provider rather than working on the boiler.
- Attempt a single boiler reset DIY safe
Press and hold the reset button for approximately three seconds, as described in your Worcester Bosch user manual. Wait for the boiler to attempt a restart. If the E2 223 code reappears within a short time, do not reset again — repeated resets will not fix a sensor fault and may mask useful diagnostic information for the engineer. Limit yourself to one or two attempts at most.
- Check system pressure is within range DIY safe
Look at the pressure gauge on the front of the boiler. It should read between 1 and 1.5 bar when the system is cold. If it has dropped below 0.5 bar, top it up using the filling loop following your user manual instructions. Very low pressure alone will not cause an E2 code, but an engineer will check this as part of any call-out.
- Inspect the sensor wiring and connector — Gas Safe engineer only Gas Safe engineer
A registered engineer will remove the boiler casing and visually inspect the flow NTC sensor connector and wiring harness. A loose or corroded plug can sometimes be reseated and the fault resolved without replacing the sensor itself, saving on parts cost.
- Test the flow NTC sensor resistance — Gas Safe engineer only Gas Safe engineer
Using a multimeter, the engineer will measure the resistance across the sensor terminals and compare the reading against Worcester Bosch's published resistance-temperature table. A reading that is open-circuit (infinite resistance) confirms the 223 fault condition; a very low resistance confirms a short circuit (222 variant). This test takes only a few minutes and determines whether the sensor needs replacing.
- Replace the flow NTC sensor — Gas Safe engineer only Gas Safe engineer
If the sensor has failed, the engineer will drain down the relevant part of the circuit, remove the old sensor from its pocket in the flow pipework, fit a new genuine or approved-equivalent sensor, and recommission the boiler. The system pressure and controls will then be checked before the boiler is returned to service.
- Inspect the PCB if the fault persists after sensor replacement — Gas Safe engineer only Gas Safe engineer
If a brand-new sensor still triggers an E2 223 fault, attention turns to the PCB, which may be misreading the sensor signal. PCB diagnosis and replacement is specialist work and significantly more expensive than a sensor swap, but it is rare for this fault code.
- Call a Gas Safe registered engineer if the fault has not cleared DIY safe
If the reset has not resolved the fault, you need a Gas Safe registered engineer to carry out the diagnosis and repair described above. You can verify an engineer's registration at the Gas Safe Register website (gassaferegister.co.uk). Do not attempt to open the boiler casing or touch internal components yourself — this is a legal requirement for gas appliances in the UK.
Parts you may need
- Worcester Bosch flow temperature NTC sensor · from £35
- NTC sensor wiring harness / connector · from £18
- PCB (control board) — if sensor tests healthy · from £280
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–£280, depending on the underlying cause.
Frequently asked questions
What is the difference between E2 222 and E2 223 on a Worcester Bosch boiler?
Both sub-codes relate to the same flow temperature NTC sensor, but they describe different electrical faults. E2 222 indicates a short circuit — the sensor or its wiring is conducting when it should not be, giving the PCB an unrealistically high temperature reading. E2 223 indicates an open circuit or disconnection — the PCB is receiving no signal from the sensor at all. In practice, the diagnosis and repair process is identical for both: a Gas Safe engineer will test the sensor's resistance and either reseat the connector or fit a replacement sensor.
Can I reset an E2 223 fault myself and will it fix the problem?
You can press the reset button once or twice to see if the fault clears temporarily, and this is described as safe in Worcester Bosch user manuals. However, E2 223 is almost always caused by a genuine component fault — a failed or disconnected sensor — so the lockout will return quickly. Repeatedly resetting without addressing the underlying problem does not repair anything and simply delays getting the boiler working properly. If the code returns after one reset, book a Gas Safe engineer.
How much does it cost to fix an E2 223 fault on a Worcester Bosch boiler?
For most homeowners, the repair involves a call-out, sensor test, and replacement of the flow NTC sensor. Expect to pay roughly £100 to £280 all in, depending on your location and the engineer's rates. The sensor part itself typically costs under £40; labour makes up the majority of the bill. If the fault turns out to be a loose connector that just needs reseating, the cost will be at the lower end. In the unlikely event the PCB is the root cause, replacement boards for Worcester Bosch boilers can add £250 to £350 to the bill — but this is rare for an E2 code.
Is my Worcester Bosch boiler safe to use when showing E2 223?
When the E2 223 lockout is active, the boiler has already shut itself down and will not fire — this is the boiler's built-in safety response to a sensor fault. You should not attempt to keep resetting it repeatedly to force it back on. Leave the boiler in lockout and arrange for a Gas Safe engineer to inspect it. There is no immediate danger to your home from the fault itself, but running a boiler without a functioning flow temperature sensor is unsafe as it removes an important temperature-control safeguard.