Home › Fault Codes › Boilers & Heating › Vaillant › F.23
F.23

Flow and return temperature spread too great

The boiler has detected an excessive temperature difference between flow and return.

What this code means

The boiler has detected an excessive temperature difference between flow and return.

Possible causes

  • Air in boiler or heating system
  • Circulation fault
  • Pump, valve or blockage problem
  • Flow or return temperature sensor fault
  • Expansion vessel issue

Common symptoms

  • F.23 displayed
  • Boiler may lock out
  • Heating circulation may be poor

Checks to make

  1. Check system pressure from the user controls
  2. Check for obvious circulation problems
  3. A competent heating engineer should diagnose pump, valve, blockage and sensor issues

Safety

  • Do not remove the boiler casing or work on gas, combustion or internal boiler components unless appropriately qualified.

Model notes

Vaillant recommends installer or engineer diagnosis.