To find the starting point for the Heat Anticipator setting, look
on the body of the furnace
gas valve. The specs should be printed in ink, and sometimes are on the back side of the valve where it's difficult to see and might require using a mirror and flashlight
. You will be looking for the amperage setting which varies with different manufacturers and models. The value on the gas valve will usually be somewhere between .25A and 1.5 A. Once you find the value on the valve, you then set the thermostat anticipator at that same setting. Be very careful not to break the fine wire underneath the "wiper"! If that wire becomes broken, the t-stat (thermostat) has been destroyed and a new one must be purchased.
Now you know more than "the average bear"!
By-the-way, many t-stats do not have a mercury switch, but rely instead on a "warp" reed which responds to temperature by flexing to open or close the contacts. Sometimes the reed is enclosed in a glass capsule similar to that which contains the mercury in the example, and in less expensive models they are just out in the open , but underneath the outer removable cover. The exposed "reed" switch is quite easily damaged and once bent also requires replacing the complete t-stat unit.
Wall t-stats in your home often have very long wire "runs" to the furnace
and wire resistance must be taken into account which requires additional steps to achieve the correct anticipator settings. In our TT's and most RV's, the wire runs are so short that wire resistance is not a problem.
Kent, thanks for your examples.
Gina, hopefully yours has just been knocked out of adjustment and not been damaged. This info might be combined with Kent's and added to the "tutorials" for future reference by others.
To everyone faced with a similar situation, seek professional help
if you doubt your knowledge and abilities to make a successful repair. Repairs are generally easier and less expensive near your "home turf" than out-on-the-road, so don't put off the inevitable!
& Ann K.