Picture of the Honeywell RTH9580WF Internet Thermostat, being snapped onto wall plate.

Honeywell Thermostat Not Turning On Heat

A Honeywell thermostat not turning on heat can happen for many reasons. A faulty thermostat, a broken heating system, power losses, damaged wiring, et al. Here, we list some of these causes, and offer repair tips to solve these no-heat issues. First, we look at what might have happened with the Honeywell thermostat itself. Then we explore the furnace issues that can also cause no heating at all.  Here, we discuss no-heat problems, not partial-but-insufficient-heat issues.  These address the case when you get no heatting at all, not the scenarios where you experience some but not enough heat.





Possible Reasons for the Honeywell Thermostat Not Turning On Heat

Summary of Causes

  1. Honeywell Thermostat Temperature Offset Set Too Large
  2. Power Failure Keeping Heat from Coming On
  3. Honeywell Thermostat Temperature Offset Set Too Large
  4. T-stat Not Level on Wall
  5. Temperature Set Too Low
  6. Bad Electrical Connections 
  7. Mechanical Thermostats can Bind Up
  8. Not Set to Desired Operational Mode (Heating or Cooling Mode)

Thermostat Temperature Offset Set Too High

Problem

The thermostat temperature display seems to show that the current room temperature never reaches the set heating temperature, and yet the heat never turns on. In this case, the display offsets may be set too high.  That is, the thermostat reads, and acts as if, the current indoor temperature is higher than it actually is. And when the t-stat thinks that the room is warmer than the set temperature, it will not turn the heat on.

Consider this.

  • Let’s say that you set the thermostat to heat to 74 degrees.
  • Further, you have set your display temperature offset to +3 degrees. This makes your thermostat display a current temperature reading that is three degrees warmer than the environment actually is. In this case, when the current house temperature is 74 degrees, the thermostat would show 77 degrees.

Now the thermostat calls for heat from the furnace when the displayed current temperature falls below 74 degrees.  But with a +3 degree temperature offset in effect, the actual room temperature must fall to three degrees below 74, before the furnace kicks on.  That is, though you’ve set the temperature to 74, you won’t actually get any heat until the room temperature falls below 71 degrees.  In apartment building situations, in which a room might easily hold a 71 degree temperature but not a 74 degree temperature, you may rarely or never feel your heat blowing.

Fixes

Decrease the display offset temperature. This helps assure that the temp reading on the thermostat shows as closer to actual room temp.  Plus, an accurate display reading helps prevent the situation where you heat does not come on enough. We suggest that you avoid setting the temperature offset to more than one degree either way (+ or – offset).





Or, just turn up the set temperature.  In this scenario, if you want your place to heat to 74 degrees, then with the +3 degree offset, you’ll need to turn the thermostat up to 77 degrees.

Power Failure Keeps Heat from Coming On

Picture of the Honeywell RTH9580WF Internet Thermostat, mounted but powered down, snapped onto wall plate.
Honeywell RTH9580WF Internet Thermostat, mounted but powered down, snapped onto wall plate.

Problem

The screen on Honeywell smart thermostats looks blank or dark. No readings or status messages appear. Further, the furnace heater does not run. Plus, you hear no humming at the furnace. But for non intelligent t-tats you may no power loss indication, except that their backlights don’t glow. Yet the effect is still the same, no heat turning on. That is, that the furnace never runs, no matter the thermostat setting.

Fixes

Honeywell thermostats often get power right from the furnace system. So, check that all furnace systems are getting electricity. Often there’s a single circuit breaker that feeds the furnace itself, and another that feeds the outside compressor unit in HVAC arrangements. So verify that all breakers are ON.

Furthermore, the heating and cooling subsystems often get electricity from separate circuit breakers. So, the thermostat could glean power from either one, although usually not both. A power outage in either system could cause Honeywell thermostat not turning on heat. By checking that the heating control circuits have power, you’ve ruled out this cause of thermostat power loss. In this way, a faulty cooling system can make the heating system fail too.

Thermostat Poorly Wired or Installed

Picture of the t-stat model RTH9580WF wall plate, mounted, but with wires not yet connected.
The model RTH9580WF t-stat wall plate mounted, but with wires not yet connected.

Problem

If the heating problem happened when you installed a new thermostat, you may have wired it the wrong way. Perhaps you’ve reversed the W and Y wires. This would run the cooling stage though the thermostat is actually calling for heating. Other symptoms may arise too. These depend on which wires and how many of them you have connected to the wrong thermostat terminals.

Fixes

Check for correct wiring at both ends of the thermostat cable. At the thermostat, affix all wires to the right screw terminals in the mounting plate. Then, do likewise at the furnace. Seek help from a professional heating technician if you feel insecure matching these wires up with the right terminals.

Thermostat Not Level May Cause Honeywell Thermostat Not Turning On Heat

Problem

Poor leveling on older thermostats can affect how well they respond to room temperature changes. Those primitive models relied on a bi-metal spring to sense temperature. Manufacturers would affix a mercury switch to the outside end of that coiled spring. Then, as room temperature rose and fell, the spring changed size, causing the outer end of the spring to move back and forth in accordance with temperature changes. This tipped the mercury switch on or off to bring room temperature nearer to the thermostat set temperature.

You needed proper leveling for this tipping to occur as designed. Indeed, if tilted too far off of plum or the horizontal, the heating system might never turn on. In this case, the mercury inside does not make the contacts as it should when the room gets too cold.

Fixes

If you still have a mercury and bi-metal thermostat, you should replace it with a current all-electronic model that has no moving parts. Today’s thermostats have more accurate sensors and many more features. Plus, modern t-stats work well, no matter how far off of level you install them. They’ll turn on the heat correctly in the house, no matter their position.  Mount them on their sides, upside down, or you can even let them dangle by the wires (although we do not recommend this).  Yet they’ll regulate your heat well, in any position.





If upgrading from an electro mechanical thermostat is not feasible, and you must fix your no-heat situation, then try drilling new mounting holes. To do that, remove the screws and wires if they get in the way. Then re position the thermostat over the new holes. Finally, drive the screws into those new holes. We suggest putting wall anchors into these holes for a stronger more permanent hold.

If your t-stat is not too far out of level, try loosening the screws that hold it to the wall. Then, slide the thermostat toward level. Then, mark the wall with an erasable pencil.  Next, while holding the thermostat in that marked position, tighten the screws again.  Finally, use an eraser to clean off any visible wall markings.

Thermostat Temperature Set Too Low

Picture of the Honeywell RTH9580WF wireless thermostat, displaying its -Home- screen, with the temperature set to 69 degrees, and in temporary hold until 10:00 PM.
Honeywell RTH9580WF wireless thermostat, displaying its -Home- screen, with the temperature set to 69 degrees, and in temporary hold until 10:00 PM.

Problem

You can set thermostats way lower than the ambient temperature in your home.  During moderate days outside for instance, you might set the heat temperature to 72 degrees.  But if you live in a tower structure, such as a tall apartment building, your apartment may never fall below 72 degrees.  Thus, your heat never comes on.

Fixes

  • If you need more heat, try setting the thermostat higher.
  • Be happy that your heat is not running any more than it is, especially if you’re paying your own energy bills.  🙂

Bad Electrical Connections Might Cause Honeywell Thermostat Not Turning On Heat

Picture of the Honeywell T8775C1005(2) thermostat wall plate, front view, showing screw terminal connection points.
Honeywell T8775C1005(2) thermostat wall plate, front view, showing screw terminal connection points.

Problem

The solid copper wires in the thermostat cable can break if flexed or bent too much. Or, maybe the installer stapled the cable with too much pressure, and shorted out the individual conductors in that cable.

This issue normally appears during new thermostat testing only. But sometimes, this problem may not show up for decades. Plus, settling of wall beams can flex these stapled wires. So, after many years, this flexing can wear wire coverings, causing faulty or no heating.

Solutions

Replace the cable between the thermostat and furnace. Avoid tightly stapling the wire, and don’t fasten it more than you must for a secure installation. Lay it loosely.





Mechanical Thermostats can Bind Up

Problem

Now and then with smart thermostats, a snap of static electricity near the thermostat, can freeze the touch screen. Also, a power surge in the home’s electrical system can do this as well. Then too, the data shown onscreen no longer updates. Further, the heating system may not come on. No matter how far from set temperature the room temperature is, the heating system may not run at all.

Fixes

Picture of the Honeywell RTH9580WF Internet Thermostat, being snapped onto wall plate.
Honeywell RTH9580WF Internet Thermostat, being snapped onto wall plate.  Snap it off the wall, and then put it back on to reboot the thermostat.

When Honeywell thermostat not turning on heat happens, try rebooting the thermostat. Turn off its power for ten to twenty seconds. Then switch it on again. This power cycling is a literal snap with many smart thermostat models.  Why?  Because they can detach from furnace power without having to unscrew them. Just unsnap them from their wall plates. Then, wait a few seconds, and finally snap them back into place to reboot. Or, if your t-stat does not come off of the wall easily, cycle off and on it at the breaker box. You can cycle main power to the whole furnace system by switching off and on the breakers that feed it. Doing this reboots the thermostat.

Not Set to Desired Operational Mode (Heating or Cooling Mode)

Picture of the t-stat, showing its -System Heat / Cool Mode Setting- screen, with the mode set to OFF.
The t-stat, showing its -System Heat / Cool Mode Setting -screen, with the mode set to OFF.

Problem

Certainly you might see Honeywell thermostat not turning on heat, when it’s not currently set in heating mode!  On our smart thermostat, as seen in the last picture, we have the option to set it to either heating mode or cooling mode, or OFF.  If OFF, you won’t get heat.  Nor will any warmth flow from your registers if set to Cool mode.

Solution

Set the t-stat’s operational mode to Heat.  On our t-stat, we do this in the System tab.  We show that screen pictured above.  Just tap the Heat option and press Done to make the new setting effective.  You should soon thereafter feel some heat.

Conclusion

As should be clear, the Honeywell thermostat not turning on heat issue in homes has many causes. Indeed, some of them fall beyond the thermostat.

But we hope that now, you know what might cause the no heat problem in your home. Knowing the causes often helps in making the right repairs as safely as possible. Even though the best fix may cost the most, now at least, you have the data in front of you. Best wishes.

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Suggested Reading

  1. Installing Baseboard Heaters Tips, Help, Instructions
  2. Noisy Window Air Conditioners, Causes, Fixes
  3. Honeywell Touchscreen Thermostat RTH7600D Review

References for Honeywell Thermostat Not Turning On Heat

  1. Why is my heat not working?  from Honeywell

Revision History

  • 2019-04-27: Added tags.
  • 2019-01-26: First published.