D1 240 — Return sensor error or short circuit

What does D1 240 mean?

The boiler's return temperature sensor has an error, or its contacts are short-circuited. The sensor might also be wet or damaged, affecting accurate temperature readings.

• Defective return temperature sensor.
• sensor contacts are short-circuited.
• sensor or wiring is wet or damaged.
• Loose electrical connections.

Click steps to track your progress.

1. 1

   Power cycle the boiler by turning it off at the mains for 30 seconds, then turn it back on.

2. 2

   Visually inspect the return sensor and its wiring for any signs of water, damage, or loose connections.

3. 3

   If the error persists, contact a qualified heating engineer to check and potentially replace the sensor.