Worcester Bosch E2 Fault Code: Causes, Fixes & Repair Costs
What does the Worcester Bosch E2 fault code mean?
The E2 fault code on a Worcester Bosch boiler indicates that the central heating flow temperature NTC (Negative Temperature Coefficient) sensor has been detected as defective. In plain terms, the boiler's internal thermometer for measuring the temperature of water leaving the heat exchanger is either failing, has lost its connection, or is sending a reading the control board cannot interpret. Because accurate flow temperature data is essential for safe, efficient operation, the boiler shuts down rather than risk overheating. Some models display a more detailed sub-code alongside the E2: the most notable is E2 222, which points specifically to a short circuit condition in the flow temperature sensor circuit, usually requiring sensor replacement by a Gas Safe registered engineer.
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 flow sensor Common
Like any electronic component, the flow temperature NTC sensor can deteriorate over time. When it fails entirely it sends either no signal or a wildly incorrect reading, triggering the E2 lockout. This is the most frequent root cause and usually requires a straightforward sensor swap by an engineer.
- Short circuit in the sensor circuit (E2 222) Common
A short circuit across the sensor terminals causes the boiler's control board to detect an out-of-range resistance value. This is what the specific sub-code E2 222 describes. Damaged wiring insulation, a pinched cable, or a sensor that has internally short-circuited are the typical culprits.
- Loose, corroded, or disconnected wiring Common
The sensor is connected to the PCB via a wiring loom with plug-in connectors. Vibration, age, or poor installation can cause these connectors to work loose or corrode, breaking the circuit without the sensor itself being faulty. An engineer can often resolve this without replacing any parts.
- Moisture or condensation ingress Sometimes
Water finding its way onto the sensor body or its electrical connector — through a minor internal leak, heavy condensation, or a failed seal — can cause erratic resistance readings or a short circuit, both of which produce the E2 error.
- PCB (printed circuit board) fault Rare
If the sensor and its wiring both test correctly, the fault may lie in the control board itself, which is responsible for reading and interpreting the sensor signal. PCB faults are less common but should be considered after all sensor-side possibilities have been ruled out.
How to fix it
- Check whether your other gas appliances are working DIY safe
Turn on a gas hob or check another gas appliance to confirm your gas supply is live. If nothing gas-powered is working, contact your gas supplier rather than attempting a boiler reset.
- Reset the boiler once or twice DIY safe
Press and hold the reset button (usually marked with a flame or the word 'Reset') for roughly three seconds until the boiler attempts to restart. If the E2 code returns immediately or after a short time, do not keep resetting — repeated resets on a sensor fault will not resolve the underlying problem and can mask important diagnostic information for an engineer.
- Check system pressure is within range DIY safe
Glance at the pressure gauge on the boiler's front panel. It should read between 1.0 and 1.5 bar when the system is cold. If it has dropped below 0.8 bar, top it up using the filling loop. Low pressure alone will not cause an E2 code, but it is worth ruling out any secondary issues while you wait for an engineer.
- Do not open the boiler casing or touch internal components Gas Safe engineer
The NTC sensor and its wiring are inside the boiler casing. Accessing them requires removing panels, and any work on the sensor, wiring, or PCB must be carried out by a Gas Safe registered engineer. Attempting this yourself is dangerous, may void your warranty, and is a legal requirement under Gas Safety (Installation and Use) Regulations 1998.
- Have a Gas Safe registered engineer diagnose and repair the fault Gas Safe engineer
An engineer will use a multimeter to check the resistance of the NTC sensor at operating temperature and inspect the wiring loom and connectors for damage, corrosion, or poor contact. If the sensor is faulty or short-circuited (E2 222), they will replace it. If the wiring is the issue, they will repair or renew the affected section. In rare cases where the PCB is at fault, they will advise on replacement or whether a new boiler makes more economic sense.
Parts you may need
- NTC flow temperature sensor · from £25
- Sensor wiring harness / loom · from £35
- Sensor connector plug and terminals · from £12
- PCB (printed circuit board) · 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 £90–£300, depending on the underlying cause.
Frequently asked questions
Can I fix the Worcester Bosch E2 fault myself?
The only safe steps you can take yourself are checking your gas supply is on, attempting one or two resets, and confirming your system pressure is correct. The flow temperature sensor and its wiring are inside the boiler casing, and working on them requires a Gas Safe registered engineer by law. Attempting internal repairs yourself could be dangerous and would almost certainly void your warranty.
What does E2 222 mean on a Worcester Bosch boiler?
E2 222 is a sub-code that appears on certain Worcester Bosch models when the boiler detects a short circuit specifically in the flow temperature sensor circuit, rather than just a general sensor failure or disconnection. The practical outcome is the same — the boiler locks out — but the diagnosis for an engineer is clearer: the sensor itself or its wiring has internally short-circuited and will need replacing rather than simply being reseated or reconnected.
How much does it typically cost to fix an E2 fault on a Worcester Bosch boiler?
Most people pay between £90 and £300 to resolve an E2 fault. A loose connection or simple sensor reseating sits at the lower end, while a new NTC sensor including parts and labour usually comes in at £120 to £200. If the PCB turns out to be the root cause, costs can rise to £350 to £500 or more, though PCB faults are relatively uncommon with this error code. If your boiler is over 10 to 12 years old and facing a higher repair bill, it is worth getting a replacement quote at the same time.
Why does my Worcester Bosch boiler keep showing E2 after a reset?
If the E2 code returns quickly after every reset, it means the underlying fault — most likely a failing sensor, a short circuit in the sensor wiring, or a damaged connector — is still present. Resetting the boiler repeatedly will not cure a sensor fault and can delay diagnosis. Book a Gas Safe engineer to test the sensor resistance and inspect the wiring; in most cases this is a relatively straightforward repair.