Worcester Bosch Greenstar 4000 System fault 281

What it means

Operation of burner and fan interrupted, category B fault.

Likely causes

1. Low primary system water pressure
2. Air in the system
3. Poor circulation within heating system
4. Faulty hydraulic connections to the pump
5. Pump wiring or operation fault
6. Incorrectly set pump rate or pump characteristic map

Where to start

1. Check primary system water pressure
2. Check for air in the system and vent the pump
3. Check for circulation within heating system