Have a round automag thermostat

It sounds like you may have a round Honeywell thermostat. It could be that the temperature pointer you see on the face of the thermostat just needs to be adjusted. The next time your furnace or AC finishes running, remove the face off the thermostat and use a small screwdriver to set the dial so the pointer temp matches the other temperature indicator.

The two blue rectangular cover plates, held on by two scews, cand be removed by taking out screws. There might be a little piece of insulation present when you pull off the panel, pull that out. You will see a pointer that is shaped kind of like an egg, pointing at numbers which represent temp in degrees. Start with the lower dial, this is your thermostat, Raise temp setting by 10 deg. Hypothetically, depending on what your present setting is, try setting lower thermostat at 130 and upper at 120. Your lower thermostat should be higher than the upper because of heat rising, it is more effecient and both thermostats don't have to be at the same temp. This will save you money in the long run.

Friend! All thermostat is calibrated to cut in and cut off at the end of - or + 1 degree end.
Example: If you set 23 degree, it will cut off in 21 degree and cut in @25 degree. So accordingly you set the temp.
Secondly, don't set temp near to your room temp.Minimum difference should be 3 degree. If your room temp 12 degree, set at least 15 degree for heat and if room temp 28, set at least 25 degree for cool.
Hope it's helpful?

What is the model number of the thermostat? What may be happening is the humidity control is trying to satisfy the humidity setting by running the a/c. In the installers set-up, there should be a setting to determine how long the system should run to satisfy humidity setting. I typically set thermostats for a 3 degree droop. Meaning it'll only drop 3 degrees below set temp. Also check your humidity setting to be sure it's not set too low. It should be set between 45% and 50%.

Make sure the switches on the back of the thermostat is set for hot water heat. If you have more then 1 zone you may a stuck zone valve or a short in the wiring somewhere keeping the boiler on.

There is a calibration method to adjust the oven thermostat plus/minus 35 degrees if it is a digital display. The method varies depending on the model range. This calibration method is used to adjust the thermostat if it is not keeping proper tempature. For example if you are setting the oven to 350 and the actual temp it is keeping is 325 then you could use the calibration method to adjust it plus 25 degrees to correct the temp. Just so you know electric ovens will keep a pretty even temp but gas ovens will vary by 40 or more degrees to keep an "average" temp. For example the burner will come on when the oven is 330 degrees and turn off at 370. 330+370 then divide by 2=350. So a oven thermometer may not show you the temp you set it at in a gas oven but does not mean the oven temp is off.

ive installed 100 new thermostats over the years and they are set from the factory.no adjusting.now some knobs have an adjustment on them.and some times customers got knobs mixed up and got the wrong one one there.

Use an oven thermometer Try to figure out if by setting it to 390 it will maintain 350 accurately. (A 25 degree change while it cycles is normal. It will probably overshoot before going off and undershoot a little before cycling on.) If so the thermostat has just drifted. Pull off the control know and look usually there is an adjustment on the shaft to change the temp showing on the knob. set it up 50 degrees. If the knob can't be changed just know that you have to adjust yourself. If it won't maintain a steady temp the thermostat is bad and will need to be replaced. The thermostat will be over $100 it may not be worth it. If this is a computer controled unit (pushbutton temp selection) the sensor needs to be replaced. This is a lot cheaper than a thermostat.

probably the element. to save wasting money, check continuity with a multimeter