Vaillant 828 Boiler F20 Code

My boiler keeps showing the following code when trying to run the central heating F20. Wondering if you have any ideas how this can be fixed?

Regards

Chris

Hi Chris,

The F.20 fault code for an EcoMAx 828 is a safety protection cut-out due to high water temperature.  During normal operation the boiler will heat the water until it reaches a maximum set temperature and cuts-out the burner circuit.  If this normal cut-out fails, the boiler will continue to heat the water until the final safety protection cut-out energises and shuts off the boiler giving you the F.20 Fault code.  Therefore in your case the maximum set temperature cut-out is not working.  This could be a controller issue or a defective temperature sensor / cable.  This is a serious issue and should be looked at by a qualified service engineer.