While you wait for answers, we may have found some information which could help you.
Click here for Ravenheat Csi 85pressure dropping on openning the hot water in my ravenheat csi 85 aboiler?
minimal hot water ?
Central heating but no hot water?
ravenheat csi 85(t) 780 series red light flashing?
ravenheat csi 120 no hot water?
Faulty Worscester 35 CDi loosing pressure?