Fault 33 Code 22 — Temperature sensors incorrectly connected (IUM)

What does Fault 33 22 mean?

The Worcester Bosch Greenstar CDi Boiler displays Fault 33 with code 22, indicating that a temperature sensor has been incorrectly connected to the IUM (Internal Unit Module) where it should not be.

• A temperature sensor is wired to the wrong terminal on the IUM
• Incorrect wiring during installation or maintenance

Click steps to track your progress.

1. 1

   Turn off the boiler's main power supply.

2. 2

   Locate the IUM and inspect its connections.

3. 3

   Remove any temperature sensor incorrectly connected to the IUM and, if necessary, insert a coding plug as specified in the manual.

4. 4

   Restore power and check if the fault clears. If not, contact a qualified heating engineer.