UL, CSA and all the rest are ONLY concerned with safety, not interference. So they have nothing to do with anything.
The FCC does however, and if the thermostat met FCC Part 15 or the Canadian or EU equivalent, then its radiation is tested and rated; right on the product. No notice of Part 15, it's an illegal product for NA sales. In addition to that, if you do have interference issues and passed Part
15, not only does the device's paperwork tell you how to control it, but gives you contact information in the event you have trouble with radiation through the air, power wires or peripheral connections. So I'd say RTFM is still something you have on your to-do list, except rather than try to slightly move the item etc., you gave it away. So often we create our own liver-quivers because emotion takes over instead of logical common sense.HTH,
Twayne