I recently had the fan changed on my Volkera Excell 80 SP Boiler everything has worked fine for about a month, however i am now getting intermitant hot water. It seems fine in the morning when i first turn the shower on but for instance if i put the cold tap on for the basin in the bathroom the shower goes cold and have problems getting hot water again .I cant get any hot water to come through the the sink in the kitchen in the morning after ive had a shower (which is the furthest point away from the boiler). It seems as thou the boiler has a mind of its own when to fire up !. The fan is running correctly as I can hear it running. Anybody got any ideas what this fault could be ?