Thermostat questions

I have a White - Rodgers manually set thermostat for my home heating unit (gas central forced air). Occassionally, the temperture shown on the thermostat consistently settles in at a temperture 4% less than what the thermostat is set at. (example: set temperture @ 70% and thermostat shuts off and maintains temperture at 66%). Would this have anything to do with the cycling of the furnace? Is it possible that the thermostat shows 66% when it really is 70% as was set?

What is the model number of the thermostat?

What other control settings besides temperature are being used--for example "cycles", or "differential".

When the heating is not running normally at setpoint, and the temperature is running consistently below setpoint, does it return to normal by itself?

More information please.

thermostat

The thermometers in thermostats are notoriously inaccurate. The only way to tell for sure is to place a reliable thermostat next to the thermostat and see what the real temperature is.

There are two solutions to this: You can adjust the anticipator, to make it cycle longer or shorter, or you can use a little screwdriver and adjust the screw behind the temperature read-out, which causes the spring-coil to loosen or tighten, depending on whether you want to raise or lower the temp. it is displaying.

Thanks to all for the responses and suggestions.

The model is 1C-330-321. I checked the setting for the anticipator and it is set just higher than .6 I have not yet checked the valve on the furnace to see what it is supposed to be set at but I have never changed it, though a heating tech that has worked on the furnace may have. (the ceramic ignitor had to be replaced).

I did download an installation and setting guide for the thermostat from the White-Rodgers web site. It had a lot of usefull info in it, including instructions for several of the comments that were posted in response to my question. I am curious about the "adjusting" the screw behing the temperture readout. In the instruction guide they refer to a lock nut that should be turned to adjust the temperture calibration.