F20 - Safety switch-off due to high temperature

What does F20 mean?

The Vaillant Ecotec Plus Boilers have shut down as a safety measure because a temperature limit has been exceeded. This can be caused by various electrical or heating system issues that lead to overheating.

• Incorrect earth connection between the cable harness and the product.
• Defective flow or return NTC sensor, possibly due to a loose connection.
• Black discharge via ignition cable, ignition plug, or ignition electrode.
• Pump not spinning correctly or a blockage in the heating system.

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.

2. 2

   Verify all NTC sensors are connected securely and check their resistance and wiring continuity if comfortable.

3. 3

   Try purging the system to remove any airlocks by activating the deaeration program (P00) on your boiler.

4. 4

   If the issue persists, there might be a blockage in the system; contact a qualified heating engineer.