Worcester Bosch Boiler b1 Error Code

Code plug not detected on Worcester Bosch boilers.

Worcester Bosch All Worcester Bosch boiler codes

May need a pro

The small code plug on the control board tells the electronics which boiler model and gas type it is fitted to. When the board can't read it (loose, wrong, damaged or a faulty PCB), it won't run.

Compatible models

Listed for Greenstar CDi Classic ErP combis, CDi Classic system and regular boilers and the HighFlow 440CDi and 550CDi ErP.

Also shown as

No other codes are listed for this fault.

Difficulty

Try the basic checks, but the usual fix is a technician's job.

How to fix
When to call a pro
Parts
FAQ

Not sure you are reading the code right? See how to read Worcester Bosch boiler codes.

Safety first: never take the casing off a gas boiler. If you smell gas, open windows, don't use light switches, turn the gas off at the meter if you can and call your gas emergency number from outside. A carbon monoxide alarm going off means the same: switch the boiler off, get fresh air and call.

How to fix Worcester Bosch b1

Call back whoever last worked on it
If an engineer has been inside the boiler recently, especially to change the PCB, let them know the code. Getting the right plug seated is part of that repair.

When to call a technician

Code plugs live on the control board inside the casing. Only a Gas Safe engineer should handle them.

Parts linked to b1

These are the parts an engineer usually checks for this code. They sit inside the sealed casing, so leave them to a Gas Safe registered engineer.

PCB (main control board)

Frequently asked questions

Which Worcester Bosch models show the b1 code?

Listed for Greenstar CDi Classic ErP combis, CDi Classic system and regular boilers and the HighFlow 440CDi and 550CDi ErP.

Can I fix Worcester Bosch b1 myself?

Only the outside checks above. If they don't clear b1, the fix is inside the boiler and needs a Gas Safe registered engineer.

Other Worcester Bosch boiler codes

Last reviewed 2026-10-21. Codes and steps can vary by model; check your owner's manual.

Sources we checked