What to check, in order
- Don't try to fix it yourself
Worcester's manual says not to try to put F0 right yourself.
- Call a Gas Safe registered engineer
Tell them the code on the display.
When to call a Gas Safe engineer
Worcester's service booklet describes F0 as an internal fault in the control board (PCB), which is replaced if the fault keeps coming back.
A repair visit will usually check the wiring first, then the boiler's control board.
Before you book
- Note the model and serial number. They're on a label on the data badge, usually under the boiler or behind the front cover.
- Write down the exact code, and what the appliance was doing when it appeared.
- Check whether it's still under warranty. If it is, the repair may cost you nothing.
Checked against
- Worcester Bosch Greenstar CDi Classic user instructions (PDF)
- Worcester Bosch Greenstar CDi Classic engineer's service booklet (PDF)
Last reviewed September 2026. Manufacturers update their pages, and your manual is the final word.