While you wait for answers, we may have found some information which could help you.
Click here for Heating Valliant Pressure
flashing f22 message?
Boiler-Valliant Ecotec Plus-won't power up, display off?
Vallient boiler showing f28 but pressure is fine?
another with a Valliant showing F22 and 0.4 bar fault?
Valliant Boiler?
Vallliant F75 error message?