Hi I have a big problem... I turn on my boiler downstairs for the hot water after about five minutes the a horrible sound coming from the loft... had a look the big tank hot water is coming back up from one of the pipes producing a hell of a noise and steaming in the tank in the loft... it is quite scary... but I have no idea of what's caused this? My boiler is new less that 12 moths old (condesing boiler) the three way vavle will that be the cause or the water pump next to the 3 way valve or the hot water cylinder? What is causing hot water flowing back up to the tank in the loft!? Help needed please asap as this is quite dangerous... haven't called anyone out yet as christmas time no one could come out...


Thanks