Worcester Bosch E2 222 Fault Code: Causes, Fixes & Repair Costs
What does the Worcester Bosch E2 222 fault code mean?
The E2 222 code tells you that the boiler's central heating flow NTC (Negative Temperature Coefficient) temperature sensor has developed an electrical short circuit or has been flagged as defective by the control board. NTC sensors act as the boiler's internal thermometers — they feed live water temperature readings back to the PCB so the boiler can regulate heat output safely. When the flow NTC shorts out, returns a signal outside its expected range, or stops responding altogether, the boiler cannot confirm that water is being heated correctly and locks out to protect itself. The 'E2' portion of the code relates specifically to NTC sensor faults on Worcester Bosch appliances, while '222' pinpoints the CH flow sensor as the affected component (as opposed to, for example, E2 221 which relates to the return NTC sensor, or E2 224 which can indicate a DHW sensor fault). If your display shows E2 222, the issue lies with the flow sensor, its wiring, or — less commonly — the PCB that reads it.
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
- Electrical short circuit in the flow NTC sensor Common
The most frequent trigger. The NTC thermistor itself develops an internal short, causing its resistance to read outside the range the PCB expects. This can happen through component ageing, moisture ingress, or heat stress over time. A multimeter check across the sensor terminals will show resistance far below the expected value at a given water temperature.
- Loose or corroded wiring connector Common
The plug-in connector linking the flow sensor to the wiring harness can work loose with vibration, or the terminals can corrode — particularly in boilers located in damp utility rooms or garages. A poor connection can mimic a short circuit and trigger the same E2 222 lockout.
- Damaged wiring harness Sometimes
The cable running from the flow sensor to the PCB can chafe against the heat exchanger casing or other internal components, eventually wearing through the insulation. A damaged wire touching the chassis or another conductor creates the short the PCB detects.
- PCB (printed circuit board) fault Rare
In a small number of cases the sensor itself tests fine but the PCB input circuit that reads it has failed, causing the board to misinterpret normal sensor signals as a short. This is a less common but more costly outcome and is usually only confirmed after sensor and wiring have already been ruled out.
How to fix it
- Check your gas supply is live DIY safe
Before anything else, confirm other gas appliances in your home — such as a gas hob or a neighbour's supply — are working normally. If you have no gas, contact your supplier rather than investigating the boiler further.
- Reset the boiler once DIY safe
Press and hold the reset button for approximately three seconds until the boiler attempts to restart. On most Greenstar models the reset button is marked with a flame symbol or labelled 'Reset'. Allow the boiler a full minute to go through its start-up sequence. If E2 222 disappears and the boiler runs normally, monitor it over the next day or two. If the fault returns, do not keep resetting — move to the next step.
- Do not attempt more than one or two resets DIY safe
Repeatedly resetting a boiler with an active sensor fault will not fix the underlying problem and may mask a worsening electrical issue. Two resets is the sensible limit before calling an engineer.
- Visually inspect the area around the boiler for obvious wiring damage (external only) DIY safe
Without removing any casing panels, check whether any cables visible at the base of the boiler or along accessible conduits show signs of damage, kinking, or scorch marks. Do not open the boiler casing — this is for observation only.
- Contact a Gas Safe registered engineer to test the flow NTC sensor Gas Safe engineer
An engineer will remove the boiler casing, locate the flow temperature sensor (typically clipped to the primary flow pipe near the heat exchanger outlet), and use a multimeter to measure its resistance. At around 25°C a healthy NTC sensor should read roughly 10,000 ohms; a shorted sensor will read near zero. This confirms whether the sensor or its wiring is at fault.
- Engineer to inspect and test the wiring harness and connector Gas Safe engineer
If the sensor resistance is within normal range, the engineer will check the connector plug for corrosion or pushed-back terminals, and trace the wiring back towards the PCB for any signs of chafing or damage. A damaged section of harness can sometimes be repaired; more extensive damage typically warrants replacing the harness.
- Engineer to replace the flow NTC sensor if found to be faulty Gas Safe engineer
Replacing the flow NTC sensor is a straightforward job for an engineer — the sensor unclips from the pipework and unplugs from the harness. Worcester Bosch OEM flow sensor assemblies are widely available from UK heating trade suppliers at roughly £20–£50 depending on the specific model. After fitting, the engineer will run the boiler through a full heat cycle to confirm the fault code is cleared.
- Engineer to assess the PCB if sensor and wiring both test correctly Gas Safe engineer
If the sensor and harness are both healthy but E2 222 persists, the fault lies with the PCB's sensor input circuit. PCB replacement is a more involved and costlier repair — see the FAQ below for guidance on whether repair or replacement makes better financial sense at that stage.
Parts you may need
- Worcester Bosch flow temperature NTC sensor assembly · from £35
- Wiring harness (model-specific) · from £55
- PCB (printed circuit board) — model-specific · 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 £100–£250, depending on the underlying cause.
Frequently asked questions
Can I fix Worcester Bosch E2 222 myself?
Not beyond a single reset attempt. The fault involves an internal electrical component — the flow NTC sensor — which sits inside the boiler casing and is connected to live wiring. Testing it requires a multimeter and knowledge of safe isolation procedures. All diagnostic and repair work must be carried out by a Gas Safe registered engineer. Attempting to open the boiler casing or handle internal wiring yourself is unsafe and could invalidate your warranty or home insurance.
How much does it cost to fix E2 222 in the UK?
For the most common repair — replacing the flow NTC sensor — expect to pay roughly £100–£250 all in, covering the engineer's call-out, labour time (usually under an hour), and the sensor part itself. If the wiring harness also needs attention, costs sit towards the upper end of that range. The outlier is a PCB fault: board replacement typically costs £350–£500 or more including parts and labour, and on a boiler aged 10 years or older it may be worth getting a new boiler quote at the same time for comparison.
What is the difference between E2 222 and other E2 codes on Worcester Bosch boilers?
On Worcester Bosch appliances the 'E2' prefix always points to an NTC temperature sensor fault, but the three-digit number identifies which sensor is affected. E2 221 typically relates to the CH return NTC sensor, E2 222 is the CH flow NTC sensor, and E2 224 can indicate a fault with the domestic hot water (DHW) sensor on combi models. The diagnostic and repair process is similar for all three, but the sensor location and part number will differ, so always quote the full code to your engineer.
Will E2 222 come back after the sensor is replaced?
In most cases, replacing a faulty NTC sensor and inspecting the wiring resolves the fault permanently. Recurrence is uncommon unless there is an underlying issue such as persistent moisture inside the boiler, a wiring harness that was not fully replaced after chafing damage, or — rarely — a PCB fault that was not identified at the first visit. An annual boiler service is the best way to spot sensor wear and connector corrosion before they cause another breakdown.