gdrummond

have domestic tank overflowing.fitted new cylinder ,header tank and new sealed system boiler about 2 years ago . never have to fill up sealed side (heating) but water pours out of domestic overflow and i mean pours like the coil in the cylinder has gone,had 5 new ball valves, overflow connection 5 inches below ,watch hot water expanding up cold feed which is the correct way for a cylinder but it keeps rising. normal y plan.i have 31 years ex ,had 2 gas technicians and 5 plumbers round who i know ,still pours out overflow any ideas?8i think it has to be the cylinder but customer has never topped up the filling loop in 2 years. cheers Graham