Newby here and I'm in trouble. Just lost my job - house up for sale and my overflow pipe is rapidly turning into a torrent!
I have a gravity fed open air system with two tanks in the attic. The smaller tank feeding the oil fired heating system is overflowing. I replaced the ballcock valve but the extra water is coming from the expansion overflow circulating back into the top of the tank. Sometimes the whole tank is full of hot water. The heating system is switched off for the summer so i presumed it was the hot water system not turning itself off. I repaced the thermostat on the hot water cylinder - no change. The overflow now happens even when the hot water timer is turned off. I dont understand what could be pressurising the system to push water up into the attic?
Can anyone help?