Calibrating Honeywell CT3600

The thermostat is mechanical using pressure from a waxstat style sender and is not adjustable.
I expect you are measuring with your probe in a different place to the sender unit; hence the differences.

On the thermostat, the two temp readings are showing two different settings, one is the setting temp that you are selecting, and the other is the room temp.

Follow the below link, select thermostat on the upper box, then type CT3600 on the lower box.

http://yourhome.honeywell.com/home/Applications/FindOwnersManual.aspx

This may prove helpful:

Rome Solarium 125 Service Mode:
Entering Service Mode
1. Hold the Hand button for 10 seconds until "Loc" is displayed
2. Press and hold the up arrow button until the numbers starting counting upward rapidly, stop at 50
3. Press the Hand button to enter Service Mode

Calibrating the Water Temperature
1. Enter service mode as per above instructions
2. Scroll to "tSC" (temperature sensor calibration) using up or down arrow buttons
3. Press the Hand button to calibrate the sensor, the current calibrated temperature will be displayed
4. Adjust the current displayed temperature reading to match the actual desired temperature using the up and down arrow buttons (leaving a few seconds between adjustments for sensor to use new setting)
For example, if tSC display reads 88 but the pool temperature is actually 86, press the down arrow twice
4. Once the selection is made, wait 10 seconds for the display to timeout and go back to the normal display

Here is a link to the user manual.

http://customer.honeywell.com/techlit/pdf/PackedLit/69-1642.pdf

Yes,
Most all the Honeywell t-stats can be calibrated...
check out this tip to find the manual for your t-stat and then how to get into the installer setup program...

Manual Honeywell How to Find Honeywell Manuals
http://www.fixya.com/support/r3894275-manual_honeywell_find_honeywell_manuals

heatman101

The thermostat is mounted in front of a hole and a void in the wall. A draft of air may be coming in from this void, where the wires are in the wall. It should be sealed so the thermostat keeps accurate temperature.
Thermostats temperature reading can be calibrated if the reading is off, as indicated by the thermostat's installation manual

Look in the manual that came with the thermostat it will give you the problem for each code.

Typically the four thermostat wires are:

R = power (or common)
G= FAN
W = Heat
Y = Cool

Assuming that you have a normal electric or gas furnace and air conditioning, if the heat really is coming on, then just switch the position of the the Yellow and White wires.

I am a honeywell dealer and this stat is obsolete and no longer supported. I am not able to pull any info on this. It might be time for a new one.