you say you have isolated the hot supply to the pump and the shower tank has stopped filling, and your tank supplying your cylinder is not filling ?
i would say cause your main tank is higher than your shower tank it is back filling the lower tank.
but only just started cause you have a non return valve in the shower on the cold side not shutting.
i would say cause your main tank is higher than your shower tank it is back filling the lower tank.
but only just started cause you have a non return valve in the shower on the cold side not shutting.