Thermostat calibration

Ken C.

... with a T-87 thermostat that was 30-plus years old. In recent months, she said she noticed that if she set the dial at 70 degrees, the room temp as indicated on the thermostat would be 72.

The heating unit was a single zone hot water boiler with a Honeywell aquastat relay control. Heat anticipator was set at 0.3. I pulled off the thermostat and found that the base was slightly off level (although it was screwed securely and likely did not shift recently).

I leveled the base and replaced the thermostat, per the customer's request. After letting the system run a while, this time the room temp matched the set temp.

My questions are, what can cause a thermostat's set temp to not match the room temp? Being out of level? The bi-metal coil being out of calibration?

Also, does the heat anticipator setting have any effect on whether or not the set temp matches the room temp?

Ron Schroeder

Also, does the heat anticipator

setting have any effect on whether or not the set temp matches the room temp?
if it is set higher than the control its attached to it will run longer cycles thereby giving a larger temp spread, set lower it will cycle less but burn out the anticipator eventually, the lower it is set the faster it will burn out.