On a hot water heating system. The heating system is split up into separate zones, heating different parts of your home, basically for every thermostat you have you will have a zone valve. (if your system uses zone valves some systems have a separate circulator pump for each zone) So if you have three thermostats in you home you should have three zone valves on you boiler.
If you have a garage unit heater that runs off your boiler then you will have
four (in some areas the unit heater zone is not controlled with a zone valve and
the water is allowed to flow freely) and if you have an indirect water heater
for your domestic hot water you will have 5.
Most zone valves run on 24 volts. There is a 24 volt transformer some place near or on your boiler that powers the zone valves.
Danger Changing a zone valve can be dangerous, you can be scalded, or electrocuted (they are not all only 24 volts) It is best to have a professional do it for you.
There are four major zone valve
manufactures. Taco, Honeywell, White Rogers, And Erie. There are others out
there, but I can't remember the last time I saw one that was not
manufactured by these companies.
This is what happens, you need heat so you turn on the thermostat this sends power to the zone valve, the zone valve opens, inside the zone valve is an end switch when the valve is opened this switch tells the aquastat relay that you are calling for heat it send power to the pump and the pump sends the hot water through the pipes to your base board or radiators. and you have heat.
The aquastat also regulates the temperature of the boiler water.
If you need additional assistance with troubleshooting or replacing your Honeywell Zone valve Please use the 24/7 Help Line