Forgive any mistakes in terminology as I try to describe my system.

I have a six zone radiant system, with a remote manifold that covers three zones, all plumbing and electric were professionally installed about two years ago during a complete renovation. Everything worked fine until recently one of the zones in the remote manifold no longer responds to the thermostat's call for heat. There is a Uponor zone control module in place that works for the other two zones. In those zones, when the thermostats call for heat, a red light goes on (which says thermostat on the Uponor unit), followed by a yellow light (which says actuator). I can hear a manual click as the switch underneath the actuator (? rectangular metal box) is triggered. But in the case of the zone that no longer is responding, the red light goes on, but there is never a response from the actuator, both in terms of physical moving of the switch or the yellow light going on.

Possibly the cause of the problem or maybe just coincidental: around this same period the thermostat for the non-working zone was flashing a low battery warning. It's one of the very basic Honeywell programmable thermostats. I replaced the batteries and snapped it back in place, checking that the wiring was still tight (just one red and one white wire). On the Uponor unit, the red led flashed for awhile then remained solid, again with no effect to the actuator. I then switched out the thermostat with an even more basic non programmable Honeywell, including the wall plate with its basic wiring. The results were the same.

I should mention that the zone is my wood shop, so the thermostat (but not the manifold) is in a dusty location. This is partly why I thought about swapping out the thermostat and sprayed it all out with compressed air.

I remember my plumber once showing me that the zones could be manipulated manually by switching that lever beneath the actuator. I thought of this as a temporary solution at least, because I use the shop for work and some activities like finishing and gluing are temperature sensitive. However, when I try to pull that switch it moves over slightly, but hits something that prevents it from going all the way to the right, and I have not wanted to experiment much more without further guidance.

I don't know if this is a problem for an electrician or plumber, or if it's something I might be able to troubleshoot without calling in someone else. Any thoughts are much appreciated!! Thank you