F23 - Safety switch-off due to large temperature difference

What does F23 mean?

The Vaillant Ecotec Plus Boilers have shut down because the temperature difference between the flow and return sensors is too great. This usually indicates a problem with water circulation within the heating system.

• The pump is blocked or has insufficient output.
• Air is trapped in the boiler or heating system.
• Flow and return NTC sensors are connected the wrong way round.
• Blockage in the boiler or heating system, including the heat exchanger.

Click steps to track your progress.

1. 1

   Check that the pump is spinning correctly; if you are able, gently check with a screwdriver to feel it spinning strongly.

2. 2

   Verify NTC sensors are connected correctly and securely; check resistance and harness continuity if comfortable.

3. 3

   Try purging the system in case of an airlock by activating the deaeration program (P00) on your boiler.

4. 4

   Drain the boiler and check the flow filter for any blockages or debris.

5. 5

   Check the rubber hoses on the flow and return to the heat exchanger; if they feel hard to touch, they might be blocked.

6. 6

   If the problem only occurs when using hot water, there might be a blocked heat exchanger requiring professional attention.