Worcester Bosch · Greenstar Si Compact ErP
F0 239Watchdog relay error
This code applies to Greenstar 25Si Compact ErP, Greenstar 30Si Compact ErP. Fault codes narrow down the likely problem, but they do not replace a model-specific diagnosis.
What you can safely check
- Do not remove the boiler case.
- Record the full code and model, then arrange a Gas Safe registered engineer.
How an engineer may fix it
Follow the model-specific fault-finding procedure, test the indicated circuit or component, repair the cause and recommission the appliance.
Manufacturer source: Worcester Bosch — Greenstar Si Compact ErP Installation, Commissioning and Servicing Instructions (6 720 813 278). Checked 15 August 2026. The appliance manual and an engineer’s on-site diagnosis take precedence. Never remove the boiler case yourself.