It is probably accidentally wired such that the end switch is energizing the coil when it closes. If it isn't wired exactly right it might end up doing that, like swapping wires since it looks like they are using a common wire to power the stat and the end switch. BTW, those mercury switch t-stats would have probably outlived all of us. If the actuator is sticking you can buy new actuators for those, they are just held on with a couple screws, don't even need to drain the system.
Zone valve hook up In their more zone valve hook; Grundfos zone valves
help wiring Honeywell Aquastat LE and 2x Taco Zone Valves — Heating Help: The Wall
If you have installed a circulating pump in your hot water system, you may have also decided that the efficient method to keep it running properly is to also install a thermostat and control. Like any thermostat, the circulating pump thermostat is used to regulate the temperature of the hot water and turn on and off the pump as necessary to ensure that hot water is appropriately flowing through your home without expending unnecessary energy. Turn off water to the circulating pump. Drain any excess water out of the system and close isolation valves that are on both sides of the circulator. Make sure that you have appropriate wiring available to hook up the thermostat. You may wish to also turn off the breaker for safety. Before you install the thermostat the pump motor shaft must be horizontal.
How to Replace a Boiler Zone Valve
Zone valve is a type of valve that is used to regulate how much water flows through a closed heating or cooling system. Generally such a system will be divided into zones, covering different parts of your home, to make the system more efficient and economical. Thus, if your house has a main ground floor with the bedrooms situated on the second floor, each of the floors representing a separate zone, you can make your system provide heat only to the ground floor during the day and just to the second floor during the night the unsupplied floor being let to cool down. This regulated distribution of heat is possible through the zone valves, which are mounted to the piping for each zone and can shut down or turn on the heat to that zone.
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