Error E2 233

Safety precautions:

- Before doing anything, switch the boiler off at the mains isolator and turn off the gas supply if you are going to remove the casing. Allow the boiler to cool. Isolate electrical supply at the fuse or consumer unit if available.

- Do not attempt to work on gas components, the burner, or the main PCB unless you are a Gas Safe qualified engineer.

- Use insulated tools, wear gloves and eye protection. If you are unsure at any point, stop and call a qualified engineer.

Initial homeowner checks you can safely do:

1. Record the exact error code and any LED/flashing patterns shown on the boiler display. Note when the fault started and any recent work or disturbances to the boiler or heating system.

2. Try a single reset using the boiler reset button or the controls. Wait for the boiler to attempt a restart and watch if the E2 reappears. If the fault returns immediately or after a short time, do not keep resetting it repeatedly.

3. Visually inspect for obvious signs of damage: check wiring runs visible outside the boiler, look for water leaks or signs of corrosion, check the boiler pressure is in the normal range (around 1–1.5 bar at rest). Low pressure is not usually the direct cause of E2 but is worth noting.

Basic diagnostic steps (only if competent and safe to do so):

1. Isolate mains power and the gas supply and ensure the boiler is cool before removing the outer casing following the manufacturer’s instructions.

2. Locate the flow temperature sensor. On Worcester Greenstar i models it is usually fitted in the flow pipe/heat exchanger area and is a small NTC thermistor with a two-wire lead and plug to the control unit. Consult the boiler manual or wiring diagram if unsure.

3. With power off, check the plug/connector to the sensor for being fully seated, corroded, bent pins or water ingress. If the connector is loose, firmly refit it and ensure the locking tab engages.

4. If you have a multimeter and are experienced using it: disconnect the sensor plug (power still isolated) and measure resistance across the two sensor pins. A proper sensor will show a finite resistance and that resistance will change if you warm or cool the sensor (for an NTC the resistance falls as temperature rises). If the meter shows open circuit (infinite) or a dead short, the sensor or wiring is faulty.

5. If you can access wiring continuity safely, check continuity from the sensor plug back to the control PCB connector to confirm the cable is intact. Look for broken strands, chafing or water damage.

6. After any reconnection, re-fit the casing, restore power and attempt one reset. Observe the boiler: if the error clears and the boiler runs normally for an extended period, monitor for reoccurrence. If the E2 returns, leave the boiler switched off and call an engineer.

When to call a professional:

- If the sensor plug is damaged, corroded or the cable is frayed or suspected to be internally broken, call a Gas Safe registered engineer to replace the sensor and/or cable.

- If the sensor resistance test shows open circuit or no change with temperature, the sensor should be replaced by an engineer.

- If wiring to the PCB is suspect or the fault persists after reconnecting and testing the sensor, further electrical diagnostics or replacement parts (sensor, connector, harness or control unit) will be needed from a qualified engineer.

Final notes:

- Do not attempt to remove or replace the flow sensor or any internal boiler parts unless you are Gas Safe qualified and competent to do so.

- Keep a record of the fault code, what checks you carried out, and any visible findings to give to the engineer. This helps speed diagnosis and repair.

- Repeated resets are not recommended; if the fault persists call a Gas Safe registered heating engineer to perform a safe and compliant repair.