What to check, in order
- Check the pressure gauge
Worcester's CDi Classic manual gives 1.5 bar as the ideal, and says the boiler may stop below 1 bar.
- Top up with the filling link
Open the filling link and let water in until the gauge reads 1.5 bar, then close it.
- Reset the boiler
Hold the reset button for 3 seconds and let go. The boiler restarts.
When to call a Gas Safe engineer
If A1 comes back with the pressure right, call a Gas Safe registered engineer. Worcester's service booklet lists a seized or sticking pump, worn pump bearings and air in the system, and says to check for leaks if the pressure is below 1.2 bar.
Good to know
- This meaning is from Worcester's service booklet for the Greenstar CDi Classic. On other Greenstar ranges, check the manual for your model.
Checked against
- Worcester Bosch Greenstar CDi Classic engineer's service booklet (PDF)
- Worcester Bosch Greenstar CDi Classic user instructions (PDF)
Last reviewed September 2026. Manufacturers update their pages, and your manual is the final word.