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What is question and what is model on thermostat?
I replied to the question on previous post you made.Did you get that reply?
OK first do you know if it has batteries and if they have replaced them if so?
yes the 6350 normally has 2 batteries inside,Have them pull front off of thermostat and replace them if they are there.
That is often the reason for erratic behavour like this.
I would start there
If that does not solve the issue, if they can get a volt meter and be ready to troubleshoot, I will be happy to guide in doing so.