TradeAssistIQHome

Worcester Bosch Greenstar 4000 System fault 811

Hot water heating: thermal disinfection failed

Gas boiler

What it means

Category A fault - thermal disinfection cycle for hot water heating failed to complete.

Likely causes

  1. Water being drawn constantly during cycle
  2. DHW temperature sensor incorrectly positioned
  3. Poor contact between DHW cylinder temperature sensor and cylinder
  4. Air in cylinder circuit
  5. DHW heating not set to priority
  6. Undersized DHW circulation line or excessive heat loss

Where to start

  1. Check that there is contact between the DHW cylinder temperature sensor and the cylinder
  2. Vent the cylinder circuit
  3. Check sizing of DHW circulation line and heat loss

The full answer, free

  • How to put it right, step by step
  • The manual page for this fault (page 74), right under the answer
Ask about 811 freeCreate a free account

Safety: Isolate gas and power before you open the case. If you have been into the gas side, do a tightness test, and a combustion and flue check before you hand back. Gas Safe (UK) or RGI (Ireland) work only.

From the Worcester Bosch manual for the Greenstar 4000 System. Check the model on the data plate before you order parts.

Other Worcester Bosch Greenstar 4000 System fault codes