We have a Honeywell T8624D Chronotherm IV Programmable Multistage Thermostat installed at our business. We use the thermostat to raise\lower tepmeratures at times which correspond with our hours of operation. The thermostat works great in the summer with A\C, however, in the winter with heat a problem exists. When the outside temperature drops the thermostat date\time settings often need resetting in the mornings when we open. It normally occurs when the temp is low enough that the heat may run after closing hours or when the heat runs to satisfy the morning setting to raise the room temperature. The installer, several heat\air contractors and electricians have tried to diagnose the problem. Any suggestions are appreciated.

Thanks in advance

Here

http://customer.honeywell.com/techlit/pdf/69-0000s/69-1074.pdf

And here


http://customer.honeywell.com/techlit/pdf/69-0000s/69-1412.pdf

Here are the manuals and instructions for your stat.

The only thing that could cause this is a power outage. This will cause the thermostat.to loose settings. Does your thermostat have battery backup? If so the batterys could be dead/weak/installed wrong.

hvac1000: Thanks for your prompt reply. I will have our current HVAC person look at the links you included. No, it does not have battery backup (which surprises me, our home thermostat has battery backup) and we have thought the problem is power loss. It seems unusual that it only happens with heat not a\c. Thanks again.