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Viessmann Vitodens 100-W fault 373

Heat transfer too low during calibration, temperature limiter shut down

Gas boiler

What it means

Burner in a fault state because heat transfer is too low during calibration, resulting in the temperature limiter shutting down the system.

Likely causes

  1. Inadequate heat transfer
  2. Circulation pump fault, scale or blockage
  3. 3-way diverter valve malfunction
  4. Air in system
  5. Faulty flow sensor

Where to start

  1. Ensure adequate heat transfer.
  2. Reset the appliance.
  3. Check circulation pump for faults, scale or blockages.

The full answer, free

  • 13 more checks in order
  • The readings and component tests from the manual
  • How to put it right, step by step
  • The manual page for this fault (page 77), 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 Viessmann manual for the Vitodens 100-W. Check the model on the data plate before you order parts.

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