Error E2

Safety first:

- Do not attempt internal gas or mains-electrical repairs unless you are a Gas Safe qualified engineer. Always isolate the boiler from the mains power before touching electrical connectors or removing covers. If you are unsure how to isolate the boiler, switch off the external isolator and turn off the room thermostat and programmer.

- Do not repeatedly reset the boiler to force it to run. Repeated resets can mask the true fault and may cause damage.

Initial homeowner checks (safe, simple steps):

1. Note the exact error display and whether the fault LED is flashing. Press and hold the boiler reset button for 3 seconds (or follow the model reset procedure in the user manual). Wait a few minutes to see if the boiler returns to normal.

2. Check the boiler display after reset. If the E2 returns immediately or shortly after, proceed to visual checks.

3. Check boiler and system pressure on the gauge. Very low system pressure can sometimes cause unusual behaviour; top up to the normal operating pressure if required, following the manual instructions.

4. Look for signs of water leakage, corrosion or damp around the boiler casing and pipework which might have affected wiring or connectors.

Visual and basic checks requiring isolation (only do if you are comfortable isolating power):

1. Isolate the boiler from mains power using the external isolator or fuse spur. Confirm the boiler display is off.

2. With the power off, remove any easily removable outer casing panels following the user manual. Only remove panels you can access without disturbing gas components. If removal requires tools or exposes gas parts, stop and call a Gas Safe engineer.

3. Locate the central heating flow NTC sensor and its plug/connector (often mounted on the flow pipe or near the heat exchanger). Check the connector for loose pins, corrosion, water ingress, chafed or broken wires, and secure seating of the plug.

4. Re-seat any loose plugs and ensure wiring is not trapped or damaged. Replace the casing, restore power and attempt another reset.

Multimeter diagnostic (only if competent with basic electrical checks):

1. With power isolated and the sensor unplugged, measure the sensor resistance with a multimeter across the two sensor pins. A faulty NTC will usually show either an open circuit (infinite resistance) or a near short (very low ohms). A correct NTC will give a finite resistance and should change if gently warmed (e.g., by holding) — NTC resistance decreases as temperature rises. Do not heat the sensor beyond hand-warm or use open flames.

2. If the sensor shows open circuit or a short, it needs replacement. If the wiring to the connector shows a short or open when tested, the wiring or connector must be repaired or replaced by an engineer.

If the above checks don’t fix the fault or you are not confident performing them:

- Call a Gas Safe registered engineer. Tell them the boiler model and that it is showing E2 (CH flow NTC sensor defective) and describe any diagnostic steps you tried. The engineer will safely isolate the appliance, accurately test sensor resistance and wiring under the correct conditions, replace the faulty NTC sensor or connector if needed, and check the control board and system for secondary faults.

Other important notes:

- Fault variants seen in service literature include codes indicating shorted sensor contacts or interrupted contacts; these point to either wiring/connector issues or a failed sensor.

- Do not attempt to bypass or jury‑rig the sensor or its wiring — the sensor is a safety and control device. Only qualified engineers should replace temperature sensors or access live circuits and gas components.

- After repair, the engineer should clear fault codes and run the boiler to confirm correct temperature readings and safe operation.