I would recommend that you shut off water supply and remove solenoid valve.Disassemble valve and clean it making sure that there is nothing stopping the valve from fully closing. If you can not find any problem after cleaning then reassemble and leave the outlet connection loose.Turn on furnace and see if the valve is even trying to close. If not then you need to replace the solenoid valve. Hope this helps. Thank you.
Answers & Comments
I would recommend that you shut off water supply and remove solenoid valve.Disassemble valve and clean it making sure that there is nothing stopping the valve from fully closing. If you can not find any problem after cleaning then reassemble and leave the outlet connection loose.Turn on furnace and see if the valve is even trying to close. If not then you need to replace the solenoid valve. Hope this helps. Thank you.