C4 237 — Control box or HCM defective

What does C4 237 mean?

The control box or Heat Control Module (HCM) is defective. These components manage the boiler's overall operation.

• Faulty control box.
• Faulty Heat Control Module (HCM).

Click steps to track your progress.

1. 1

   Reset the boiler by turning off the mains power for at least 30 seconds, then turn it back on.

2. 2

   If accessible, ensure that the Heat Control Module (HCM) is properly seated in its slot.

3. 3

   If the error persists, contact a qualified heating engineer as the control box or HCM may need replacement.