Thermostat displays E3 and cannot control hot water temperature from the cylinder sensor.

Safety first: Turn off power to the heating system at the main isolator. Cylinder sensors are usually low voltage but are connected within mains wiring centres.

• Locate cylinder sensor: Find the Drayton cylinder sensor strapped to the hot water cylinder (often under insulation).
• Check connections: At the wiring centre, identify the cylinder sensor terminals (refer to the Drayton wiring diagram) and ensure the screws are tight and wires are not corroded.
• Inspect cable run: Look for damage where the cable passes through grommets or clips. Repair or replace damaged sections.
• Measure resistance: Disconnect the sensor leads and measure resistance with a multimeter. Compare to Drayton’s NTC chart for the approximate cylinder temperature. Infinite or near-zero readings indicate a faulty sensor.
• Replace sensor: Fit a new Drayton-compatible cylinder NTC sensor, strap it firmly to the cylinder with good thermal contact, reconnect at the wiring centre, and restore power. Confirm the thermostat now reads a sensible cylinder temperature and E3 is cleared.