Error E2

Safety precautions:

1) If you are not comfortable working around boilers, stop and call a Gas Safe registered engineer. Do not attempt gas-side repairs or anything that involves the gas valve, burner or sealed heat exchanger.

2) Before touching any internal parts, isolate the boiler electrical supply at the fused spur or consumer unit and turn off the boiler. Never work on live wiring. If you do remove the casing, ensure the power is off and you follow the manufacturer’s instructions.

3) Keep children and pets away; wear eye protection and use insulated tools.

Initial checks a homeowner can do (no internal access required):

1) Note the exact fault: record the displayed E2 and any additional cause code from the information menu if you can (press the spanner/return or info button per manual). This helps the engineer.

2) Try a simple reset: press and hold the boiler reset button for 3 seconds (or follow the reset method in your manual). If the fault clears and stays cleared, monitor the boiler — if it returns, that indicates an ongoing issue.

3) Verify that external controls are calling for heat: thermostat set above room temperature, timer on, and any room stats or smart controls are calling for heat. If there is no call for heat the CH sensor will appear irrelevant.

4) Check system pressure on the gauge — very low pressure can cause other faults and confusion; restore to normal if required following the manual, but only if you are comfortable doing that.

5) Visually inspect any exposed sensor wiring or visible cable runs for damage, kinks, water ingress or corrosion. Do not open the boiler cover solely to probe gas or electrical components unless you are competent and the power is isolated.

Specific diagnostic steps (for competent DIYers only; otherwise skip to the professional section):

1) Isolate electrical supply to the boiler at the fused spur or consumer unit and ensure the boiler is fully de-energised.

2) If the manual permits and you are comfortable, remove the outer case to access the internal components. Follow the manufacturer’s instructions to avoid damaging seals or components.

3) Locate the CH flow NTC sensor: typically fitted to the primary flow pipe or near the flow outlet from the heat exchanger. It is a small probe with a two-wire connector or plug.

4) With power off, disconnect the sensor plug from the wiring harness and inspect both the plug and socket for bent pins, corrosion, moisture or loose wires. Clean gently if corroded and dry thoroughly before reconnecting.

5) Use a digital multimeter on the resistance (ohms) setting to test the sensor across its two terminals. NTC sensors change resistance with temperature (resistance decreases as temperature rises). You can gently warm the sensor (warm cloth or your fingertip) and watch for a change in resistance to confirm responsiveness. If the meter shows an open circuit (very high/infinite resistance) the sensor is likely disconnected/broken. If it shows a near-zero reading (short) it is likely shorted. If it shows a steady, plausible resistance that changes with temperature, the sensor is probably OK and the fault may be wiring or control related.

6) Reconnect the sensor securely, reassemble the casing if removed, restore power and attempt a reset. Observe whether the E2 returns and note any additional cause codes (e.g., shorted vs disconnected codes often have subcodes).

When to call a professional and what they will do:

1) If the reset does not clear the fault, if the sensor tests indicate open or short circuit, if you found wiring damage, or if you are not comfortable opening the boiler, call a Gas Safe registered engineer.

2) The engineer will carry out safe isolation, full electrical and resistance testing, confirm whether the sensor, connector or wiring needs replacing, and if necessary replace the CH flow NTC sensor with the correct Worcester Bosch part. They will also check the control module/PCB if sensor and wiring are OK, and verify the boiler operates safely after repair.

3) Give the engineer the exact E2 fault and any cause code you recorded, describe what checks you performed and any visible issues you noticed. This saves diagnostic time.

Final notes:

- Do not attempt gas-side or complex electrical repairs yourself. Replacing an internal sensor or repairing wiring inside the boiler should be done by a Gas Safe engineer to ensure safety and warranty compliance.

- Keep a record of the fault, the reset attempts and any tests you carried out for the engineer. This helps speed up diagnosis and repair.