Hello! We have a oil fired heating system (new boiler last year) with a HW cylinder. Both the two way valves for the CH and HW have been replaced but when the HW comes on the radiators around the house get hot. The CH 2 way valve is 100% closed when the HW comes on and the copper pipe the other side of the CH 2 way valve remains cool. How is the CH system getting hot with the CH 2 way valve remaining closed?