I had a problem with boiler not operating during hot water demand. Central heating is fine. I switched off boiler for a minute and switched it on again and got continued hot water from Kitchen and bathroom sink and for a while in the bath. But after a while water in bath turned cold. Now I can only get hot water in the bath when I turn on the bathroom sink cold water at full tilt. Is this a pressure problem? My Boiler is Worcester Bosch - Greestar 24ijunior / 281junior