I have a problem with one of the zone valves for my hot water heating. The heating company identified it as a zone valve. The power head is bad. It looks pretty old but I found a matching replacement. Honeywell V8043F 1051. Should I beable to swap the powerheads out? Will I need to drain the system? I prefer to purchase the whole valve so that if the power head doesn't fix it, I still have the option to replace the whole valve.