Error E2 350

Safety precautions:

1) If you are unsure or uncomfortable at any time, switch the boiler off and call a Gas Safe engineer. Do not work on gas valves, burner or any sealed gas parts unless you are qualified.

2) Isolate electrical power to the boiler before removing the casing. Wait for any hot parts to cool. Take care as some components may still be live if internal isolation switches are present.

3) Do not bypass or short sensors to force the boiler to run — this defeats safety checks and is dangerous.

Initial checks a homeowner can do (no tools or minimal tools):

1) Note the exact fault code and whether the fault LED is flashing. Take a photo of the display for the engineer.

2) Try a single reset: press the boiler reset/spanner button once, wait a few minutes and see if the code returns. Do not repeatedly reset the boiler more than once or twice as it may mask intermittent faults.

3) Check for obvious signs of water ingress, corrosion or loose wiring around the external pipework leading to the boiler and any visible parts of the boiler beneath the casing (do not open the boiler yet if you are not competent).

4) Check system pressure on the front gauge. Low pressure is not the primary cause of E2 but logging other system symptoms is useful for the engineer.

Specific diagnostic checks you can attempt if you are competent with basic electrical checks (only if comfortable and after isolating mains power and removing outer casing):

1) Locate the CH flow temperature sensor: typically it is clipped to the flow pipe or mounted into the flow manifold inside the boiler. It will have a two-core cable and a plug/connector to the control PCB.

2) Visually inspect the sensor plug and wiring for pinched/crushed cables, burnt or corroded contacts, moisture or signs of leakage. Reseating the connector (disconnect and reconnect) can resolve poor contact — do this only with mains isolated.

3) With the mains isolated and a multimeter available, measure the resistance of the sensor across its two pins. At normal room temperature an NTC flow sensor used by Worcester is commonly around 10 kΩ at 20–25°C (values can vary by model — check appliance manual if available). An NTC shows higher resistance when cold and lower resistance when warm. If the meter reads very low resistance (near 0–a few ohms) that indicates a short. If it reads open circuit (infinite resistance) that indicates a broken/open sensor or broken wire.

4) If the sensor appears shorted or open, trace the wiring back as far as possible to check for damage, chafing or water ingress in the cable. If the wiring to the PCB is damaged, do not attempt to repair gas-related wiring yourself — isolate and call an engineer.

5) After replacement or repair by an engineer, the technician will confirm correct sensor resistance, check the PCB input, wiring harness and will replace the flow NTC or faulty connector/cable as required.

When to call a professional and what to tell them:

1) Call a Gas Safe registered engineer if the reset does not clear the fault, if you confirm the sensor is shorted or open, or if you find damaged wiring or moisture. Sensor replacement and internal checks of the control PCB and wiring are tasks for a qualified engineer.

2) When you call, tell the engineer the exact boiler model, the E2 350 code, whether the code was intermittent or permanent, and any visual findings (wet components, corroded connector, low system pressure, pictures). This speeds up diagnosis and repair.

Final notes:

1) Do not operate the boiler long-term with a known sensor fault or attempt to bypass the sensor — the safety and regulation systems rely on correct temperature sensing. Leave the boiler switched off if you suspect internal damage until an engineer attends.

2) The usual remedy is replacement of the faulty flow NTC sensor and/or repair of the connector or wiring; in rare cases the control board input may need checking. All replacement work should be completed and certified by a Gas Safe engineer.