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Worcester Bosch Greenstar 4000 Combi fault 2964

Flow rate in heat exchanger too low

Gas boiler

What it means

Flow rate through the heat exchanger detected as too low.

Likely causes

  1. System not filled
  2. Air locks in system
  3. Faulty heat exchanger sensor
  4. Damaged harness

Where to start

  1. Check the flow through the appliance and that the system is filled
  2. Check for air locks in the system and purge if required
  3. Check the heat exchanger sensor (primary thermistor) and the plug connected to the temperature sensor

The full answer, free

  • 2 more checks in order
  • How to put it right, step by step
  • The manual page for this fault (page 78), right under the answer
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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 Combi. Check the model on the data plate before you order parts.

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