The Honeywell zone valve end switch is a little button inside the zone valve that is pressed when the zone valve is fully open. When this button is pressed it sends a signal to the boilers control or a circulator control that tells the boiler there is a call for heat.
If you look close at the image above you will see the words end switch stamped into the zone valve the two wires tied to the two terminals go to the T T terminals on the aquastat relay or to a circulator control or to 2 wires on the thermostat relay also known as a fan center, even though there is no fan. Some Honeywell zone valves do not come with the power block seen in the above image, but come with 2 yellow wires and 2 red wires. The red wires are the end switch wires and the 2 yellow wires are for the zone valve motor.
Note the lever under the power block. All Honeywell zone valves have this lever. It can be used to manually open a zone valve you just slide it over and hook it in to the little hook on the right. Even though this will allow water to flow through the zone valve, it will not depress the end switch button. the zone valve needs to be opened by power to open far enough to depress the end switch button
At this point we need to review where we are. All thermostats are turned up as far as they will go. The Pilot light is lit. The gas control valve is in the on position. You have power or are assuming you do for now. The boiler is cold.
Now slide the lever on your zone valves, if the lever moves easy with out
much resistance the zone valves are open from the power source. This means
your thermostats are working and the transformer for the zone valves is also
working. Please note many times a separate 24 volt transformer is used for
the zone valve, and some times (if you have many zone valves) you will have
more then one transformer for the zone valves alone and a 24 volt
transformer for the boiler functions. Sometimes there is only one 24 volt
transformer that controls all of the boiler functions and opens all of the
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