This thermostat was installed only 8 months ago and has worked fine until last night. It began a humming sound and the thermostate vibrates. What is causing this? The heater is working fine and all displays are normal. It is just this loud sound that is emitting from the thermostate itself and the vibration that is new.

Never heard of this problem before and I have been around the heating trade for many many years.

Sounds like something is loose inside and responding to the 24 volts AC. Do you have a warranty on it?

The thermostat is under warranty. I have left a message with the installer and hope to hear back from them today. Thanks for your insight.