Fault 12 — Cylinder High Limit Thermal Cut-out tripped

What does Fault 12 (High Limit) mean?

The Worcester Bosch Greenstar CDi Boiler controller displays Fault 12, indicating that the cylinder temperature has reached an excessively high level, causing the high limit thermal cut-out to trip as a safety measure.

• Cylinder temperature is too high
• High Limit Thermal Cut-out has tripped

Click steps to track your progress.

1. 1

   Turn off the boiler's main power supply.

2. 2

   Locate and reset the High Limit Thermal Cut-out according to your boiler's instructions.

3. 3

   If the fault persists after resetting, contact a qualified heating engineer to diagnose further.