Picture of the Honeywell RTH9580WF thermostat, displaying its -Waiting for Equipment- message, highlighted.

Thermostat Reading Higher than Setting Problem

When a thermostat reads higher temperature than its temperature setting, your home can get too cold in the winter and too warm in summer.  Now at least several factors affect the thermostat temperature reading besides actual room temperature.  These include aging components drifting out of tolerance in older thermostats.  Or, an improperly placed thermostat might read a higher temperature than what it’s actually set to maintain. Also, broken electronics or lopsided thermostat installation (not level), cause erroneous readings.  So here, we discuss some of these problems and offer suggestions for fixing them, to address this annoying and potentially costly issue.

Why do you see a Thermostat Reading Higher than Setting, and How to Fix

We offer these causes and fixes in  order of severity.  That is, the most involved or costly problems appear near list bottom.  The simpler fixes and cost-free tweaks appear we put near the top.

First, Check that your Thermostat is Indeed Reading Wrong

To start, get an accurate thermometer.  Then, place it as close to the thermostat as practical.  This assures that it is reading the same air temperature that the thermostat sees.  We use an inexpensive refrigerator thermometer for this purpose, as shown next.

But for the absolute BEST results, get a thermometer that reads in the 70-degree range midway up its scale.  Also, be sure it’s large enough for you to read with ease.  You want to be far enough away from it so that your warm breath does not affect the temperature readings.

Picture of a Honeywell smart thermostat alongside a reference thermometer. This makes it easy to compare the temperature your thermostat reads with the reading from a known-good thermometer nearby.
A Honeywell smart thermostat alongside a reference thermometer. This makes it easy to compare the temperature your thermostat reads with the reading from a known-good thermometer nearby.

Now to the causes and fixes of incorrect thermostat temperature readings.

1. Assure that Thermostat Vents are Not Blocked by Dust, Lint, Curtains, Furniture

Picture of the Honeywell RTH9580WF Internet t-stat, being snapped onto wall plate.
Honeywell RTH9580WF internet t-stat, being snapped onto wall plate.

This is of big concern in modern day thermostat models, that generate some heat from the microprocessors, memory, and other computer components inside.  If the vents are blocked by dust, furniture, Etc., the thermostat can grow extra warm inside, where the temperature sensor is found.  Thus, this vent blocking can cause higher-than-normal temperature readings.

The solution is to keep your vents open.  Vacuum the thermostat once per season, or more often if your thermostat is in a dusty, “linty” location.  Or, remove the cover and gently blow out the inside with canned air.  Or, if you don’t have canned air, use a soft, fine bristled brush and GENTLY brush out the dirt.  Note however, that some thermostats have no vents on the sides. For these, take them off the wall, and dust out in back of the unit.

2. Thermostat May Need Calibrated

Picture of the Honeywell RTH9580WF thermostat, displaying its -Indoor Display Offsets- screen with a minus 1 degree temperature offset highlighted.
Honeywell RTH9580WF thermostat, displaying its -Indoor Display Offsets- screen with a minus 1 degree temperature offset highlighted.

See our post  How to Calibrate Honeywell Thermostat Temperature RTH9580WF  for details.  This explains how to assure that your thermostat is adjusted correctly for reading the right room temperature, for a typical digital smart thermostat.  A temperature offset that is too far in the negative can make the thermostat read a few degrees higher than the actual temperature in the room.

Follow the instructions in your thermostat’s manual to adjust its display offset temperature reading.

3. To Fix the Thermostat Reading Higher than Setting Problem, it Might Just Need Leveling

Picture of the Honeywell Smart Thermostat RTH9580WF wall plate, mounted, with wires connected.
Honeywell Smart Thermostat RTH9580WF wall plate, mounted, with wires connected.

While leveling is not as important with today’s digital thermostats, we suggest  that you check that your thermostat is indeed level, especially if yours is reading higher than its actual setting.  Not only does leveling improve its appearance.  It also increases airflow through the thermostat vents, helping to ensure accurate temp readings.

If its manual says to level it, then by all means, make sure the thermostat is level (horizontal and plum).  Sometimes you can get away with simply loosening its mounting screws enough to re position the unit. But if that doesn’t give you enough leveling play, then remove the unit from the wall and make new, more level screw holes for it.

4. A Broken Thermostat Temperature Sensor can cause Higher than Setting Reading

All thermostats have some form of sensing device that detects the temperature near the thermostat.  Now in today’s t-stats, a temperature sensitive resister such as a thermistor or varistor, can start to offer different resistance values for a given temperature.  This confuses the thermostat, misleading it into reading a higher than actual temp.

Older thermostats also have a sensor.  But this is usually a mechanical bi-metal spring attached to a reading gauge needle.  Some of these may offer a calibration adjustment.  But others, especially if they become bent due to tampering, are best just replaced.  Many of these mercury thermostats have two sensors.  One reads the temperature for viewing.  The other tips the mercury switch on and off as the room heats and cools. In these models, a faulty spring in the visual thermometer portion of the unit can cause a temperature reading that is higher than the set temperature.

In any case though, if you have one of these mechanical thermostats, we highly recommend that you buy a newer, all-electronic model.

5. Thermostat is in Drafty, Extra Warm or Cool Location

Keep all heat or cold-producing appliances well away from your thermostat.  That includes microwave ovens, stoves, sunlamps, most fans, hair dryers, radios, — ANYTHING that produces heat!

Furthermore, do not allow sunlight or lamplight to shine directly on your thermostat, as these can make higher than setting reading. Keep candles and auxiliary heaters away!

Also, do not install a thermostat on exterior walls or near windows and doors, as the outside climate will impact the accuracy of thermostat temperature readings.  Keep it away from heated pipes and ducts as well.

Hire an HVAC technician to relocate your thermostat to an interior wall that does not get any direct heating or cooling from the furnace / AC system that it controls.  Mount it approximately five feet above the floor

6. Faulty Wiring can Cause Excess Heat in and Around the Thermostat and cause Reading Higher than its Setting

Picture of a common t-stat wall plate, mounted, but with wires not yet connected.
A common t-stat wall plate mounted, but with wires not yet connected.

In rare cases, incorrectly wired thermostats have been known to cause higher than expected temperature reading.  This can happen if, for some reason, the wires inside the thermostat housing get warm due to excess current; often caused by a short.

Check that the thermostat is cool to slightly warm to the touch.  It should never be very hot.  If it is, then call a qualified HVAC repair person immediately to check the wiring.  Excess warmth could present a fire hazard, which obviously, you should fix  as soon as possible.

Conclusion for Thermostat Reading Higher than Setting Problem

If a thermostat reads higher than actual temperature, don’t take it lightly.  Fix it right away.  Why?  Because this issue can seriously impact how comfortable you feel in your home.  How?  It can make you feel extra cold all year round.  And, especially in the summertime, your air conditioning may run excessively, raising your energy bills.  In winter, it can cause your furnace not to run enough, causing excessive coldness in your living quarters.  So do it up right, and make sure all is well with your thermostat.  Check that it’s reading the right temperature at least once per year, keep it clean and level, and free of any blockages around its vents.

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References for Thermostat Reading Higher than Setting

  1. Why Does my Thermostat Read the Wrong Temperature?   From Hyde AC

Revision History

  • 2019-04-15: Shortened post URL and tweaked key phrase targeting.
  • 2019-02-05: First published.