Strange multi-zone issue
I'm having a very weird issue with my multi-zone setup. I previously had just a single Smart Thermostat controlling all my downstairs zone, and a wired stat to control everything upstairs.
Today, I replaced the wired stat upstairs with another Smart Thermostat controlling all the upstairs zone. However, now when I turn on the heating upstairs, the downstairs Smart Thermostat also triggers, resulting in the radiators in BOTH zones heating up.
Any ideas on what's going on?