A5 — Tank NTC sensor defective

What does A5 mean?

The negative thermistor coefficient (NTC) sensor for the hot water tank is faulty. This sensor measures temperature and affects hot water operation.

• Defective NTC sensor.
• Damaged or loose wiring to the sensor.

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

   Check all visible wiring connections to the tank NTC sensor for tightness and damage.

3. 3

   If the problem continues, contact a qualified engineer to test and replace the sensor if necessary.