Hydronic Heating System Zone Valve Repair - Micro Switch

Last week I realized a Caleffi  Z-One zone control valve for our main in-floor hot water heat wasn't functioning correctly, so I'd pulled the valve control box off the valve and when I tested its internal micro switch, I found that it wasn't working reliably. The micro switch is responsible for turning on the recirculating pump on the heating system after the zone valve opens. Without the pump coming on, there would be no heated water flowing through the pipes to heat this zone. I ordered a new switch online (takes a week to get it).

The switch came in the mail today so I am tackling the job of replacing it. I first documented which wires go where...

... then popped off the box by pressing the gray button and pulling the box up and off the valve. The thin lever behind the gray button is to manually open the valve, or to check at a glance the position of the valve at any time.

Removing the top cover shows the 24-volt AC synchronous motor.

Two screws, and the motor comes off.

Then the aluminum housing can be pulled off, shown below. Be careful to not let the gears come out of their positions, or you will have to rewind the internal spring to some indeterminate tension level. Don't ask me how I know... And the little copper wire seen on top of the micro switch in the photo below act a shim in the two holes of the original switch to move it closer to the operating cam. The first time I had this thing apart I'd elongated the holes in the switch with a small drill in the drill press, then inserted the copper wire to position the switch closer to the cam. I did that modification last week to get by until the new switch showed up.

The replacement micro switch on Ebay was $12 shipped, same brand and nearly the same part number. A complete new control box is $70 on Amazon.

The new switch's button didn't poke out as far as the old switch so I checked to make sure the contacts were being closed when the valve mechanism was cycled. It worked as it should.

Next the wires were moved from the old switch to the new one.

All is back together...

... and back on the valve. I turned up the thermostat and the valve worked like a charm.