Vaillant boiler f20 fault

vaillant boiler f20 fault

The F20 error indicates an emergency shutdown due to tripped safety temperature limiter  STB. It is deactivated when temperature exceeds the admissible level.

It can happen due to loose wire harness connection, faulty flow or return NTC thermistor power line. Also, this may be due to damaged ignition lead, electrode or ignition connector.

This error is hard to clear without professional help.