Picture of a Honeywell thermostat not reaching set temperature, with the set temperature at 83 degrees while the current temperature Is 77 degrees.

Honeywell Thermostat Not Heating Up, How to Fix




A Honeywell thermostat not heating up your home can happen for many reasons. Poor thermostat placement, to a broken heating system. Here, we list some of these causes. We then offer troubleshooting techniques and repair hints to solve these heating issues. First, we look at what might go wrong in the Honeywell thermostat itself. Then we talk about the furnace issues that can also cause too-low heating levels.



Possible Reasons for the Honeywell Thermostat Not Heating Up the House

Thermostat Not Level May Cause Honeywell Thermostat Not Heating Up your House

Problem

Poor leveling on older thermostats can affect how well they respond to room temperature changes. Those models relied on a bimetal spring to sense temperature. They attached a mercury switch to the end of that spring. Then, as room temperature rose and fell, the spring changed size. This tipped the mercury switch on or off to bring room temperature near the thermostat set temperature.

You needed proper leveling for this tipping to occur as designed. Indeed, if tilted too far off of level, the heating system might never heat up at all. In this situation, the mercury inside does not make or break the contacts as it should.

Fixes

Level your Honeywell thermostat if it is not already level. If it’s not too far out of level, try loosening the screws that hold it to the wall. Then, tilt it toward level. Finally, while holding the thermostat in that position, tighten the screws again.

But if the thermostat is too far from level, drill new mounting holes. To do that, remove the screws and wires if they get in the way. Then reposition 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 hold.

If you still have a mercury thermostat, it may be time to replace it with a current model. Today’s thermostats have more accurate sensors and more features. Plus, these newer ones work well, no matter how far off of level you install them. They’ll warm the house correctly in any position.



Honeywell Thermostat Lost Power

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. There may be no indication of power loss on today’s non programmable thermostat models, except that their backlights don’t light up. But the effect is still the same. That is, that the furnace warms your home not at all, no matter the thermostat setting.

Fixes

Honeywell thermostats get power from the furnace system usually. So, check that all parts of that furnace have power. Often there’s one circuit breaker that feeds the furnace itself, and another that delivers power to the outside unit in heat pump setups. So check that none of these has tripped out.

Check that the heat works. The heating and cooling subsystems often get power from separate circuit breakers. So, the thermostat could get its power from either one, although usually not both. A power loss in either system could cause Honeywell thermostat not heating up the home. By checking that the heat works, 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 Not Calibrated Correctly Might Cause Honeywell Thermostat Not Heating Up the House

Problem

The current temperature reading on the thermostat may not show actual room temperature. Think about your heating system. The thermostat reads high. That is, it reads 76 degrees when the actual room temperature is 72 degrees. Here again, the furnace may be not run at all because the thermostat thinks that the home is warmer than it actually is.  So, the furnace will not raise room temperature further. Thus, the thermostat never heats up your home to comfortable levels for you.

Fixes

Calibrate your Honeywell thermostat on those models that support this. To calibrate the thermostat, buy an accurate thermometer. Then, place it near the thermostat. Next, wait for a half hour for the readings to stabilize. Then, note the difference in reading between the thermometer and the thermostat reading. In the 72 degrees Vs. 76 degrees example above, the difference is four degrees. If the thermostat reads four degrees warmer than the thermometer, then adjust thermostat calibration four degrees in the negative. If the thermostat reads four degrees cooler, then adjust the reading four degrees in the positive.




Thermostat Badly Wired

Problem

If the heating problem happened when you installed a new thermostat, you may have erred in how you wired it. 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, attach all wires to the right terminals in the wall plate. Then, do the same at the furnace end. Get help from a professional heating system repairman if you feel insecure matching these wires up with the right terminals.




Broken Thermostat Wiring can Cause Honeywell Thermostat Not Heating Up Your Home

Problem

The solid copper wires in the thermostat cable can break if flexed too often. Or, perhaps the installer stapled the cable with too much pressure or stapler misalignment, and nicked the cable.

This issue normally shows up during new thermostat testing. But sometimes, it might not surface for years. Plus, settling of wall studs can flex these wires that installers often fasten to them. So, after decades, this flexing can wear wire coverings, causing faulty furnace heating operation.

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.



Honeywell Thermostat Temperature Offset Set Too Large

Problem

The thermostat temperature display seems to show that the current room temperature never reaches the set heating temperature. In this case, your heating system may indeed be heating to your desired temperature, as it should.  But if you go by the thermostat’s current temp readout, your home appears to never warm to that set temperature.

Now, consider the following.

  • Let’s say that you set the thermostat to heat to 75 degrees.
  • Further, you have set your display temperature offset to -3 degrees. This makes your thermostat display a current temperature that is three degrees cooler than it actually is. In this case, when the current house temperature is 75 degrees, the thermostat would show 72 degrees.

Now regardless of your temperature display offset setting, the thermostat still calls for heat from the furnace until the actual room temperature reaches 75 degrees.  Then, it would stop heating further when the thermostat temperature readout reaches 72 degrees, not 75 degrees. Thus, the reported room temperature on the thermostat display, would never reach the set temperature (75) because the thermostat shuts off the heat when the actual temperature hits 75 degrees. So, a large temperature offset can look like a Honeywell thermostat not heating up issue. But it isn’t here. The thermostat is actually heating correctly.  It’s just that the lower display reading makes it appear that it’s not.

Fixes

Decrease the display offset temperature. This helps assure that the temp reading on the thermostat reads close to actual room temperature.  Plus, an accurate display reading helps prevent exceed your furnace’s heating capacity. Avoid setting the temperature offset to more than one degree either way (+ or – offset).



Mechanical Thermostats can Seize 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 the same. 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

When Honeywell thermostat not heating up the house happens, try rebooting the thermostat. Turn off power to it for ten to twenty seconds. Then switch it back on. This power cycling is simple with many smart thermostat models because they can detach from furnace power. Just unsnap them from their wall plates. Then, wait a few seconds, and finally re-attach them to reboot. Or, if your Honeywell thermostat 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.

Thermostat Temperature Set Too High or Too Low

Problem

You can set thermostats way lower than the heating system can deliver. During a cold time outside for example, you might set the heat temperature to 74 degrees. But your furnace moves only enough BTUs to heat to 72 degrees.

Fixes

  • Try setting the thermostat to a realistic temperature for your furnace. A realistic temp is one that your home heaters can reach based on current weather conditions. If that setting does not feel comfortable, then your furnace may be at fault.
  • So, check your furnace for proper working as discussed elsewhere in this piece, and fix as needed.

If you do these things but still want higher temps in the home, then try the following.

  • Add more heaters around the house, such as electric baseboard heaters or portable space heaters.
  • Or, upgrade the central heating unit to a larger size.  Discussed more in the next section.
  • Add more insulation around your home.
  • Install better sealing windows and doors can also raise the high temperature in your home that your furnace can reach.




Furnace Issues can Cause Honeywell Thermostat Not Heating Up your House

Clogged Furnace Filters and Fan Blades

Problem

Dirty air filters can constrict airflow though the furnace’s heat exchanger. Clogged filters reduce how much the furnace heats. How so?  Dirty filters and fan blades move air less well. Plus, they make more noise besides.

Fixes

  • Replace furnace filters monthly.
  • Plus, hire a pro home heating technician yearly, to check your furnace. He should clean out dust buildup inside.
  • Also, have him remove blockages in the air hander, inspect the control units for damage, clean out air ducts, check heat registers around your home for clogs, and so on.




Wrongly Sized or Worn Furnace System can Cause Honeywell Thermostat Not Heating Up your Home

Problem

Sometimes, home builders cut corners to cut costs when figuring furnace size. They want the cheapest furnace they can get by with.  Sadly, these cheapo models are often too small thus, to control the heating temperature well. So, on very frosty days, you might see the Honeywell thermostat not heating up problem show up.

Also, over time with heat pumps especially, their compressors lose efficiency. Why? Because either their valves start leaking. Or the refrigerant leaks out through small holes in the piping.  As more refrigerant leaks away, the less efficient the heating system becomes.

Fixes

  • Have an HVAC tech check refrigerant pressure and fill with enough refrigerant to bring this reading into line with what the HVAC system specs say it should be.   This value differs depending on the model of heating system you have.
  • The tech should also read the head and tail pressures while the compressor runs. Find the right values for all of these on a sticker somewhere inside the HVAC unit.  If the ratio between head and tail pressure is too low, it may be time to replace the compressor.
  • Also, the changeover valve might be cheap enough to replace. So too would the compressor. This repair may be the right thing to do as long as the system is less than fifteen to twenty years old. But if it is older, then replace the whole system.




Dirty or Frosted Heat Pump Coils can Trigger Honeywell Thermostat Not Heating Up your House

Problem

Dirty heat pump coils, again, slow airflow through the condenser outside, and the evaporator unit inside. Thus, dirt can interfere with the heating system’s efficiency. Dirty coils lowers the BTUs per hour that a heat pump can pump for example. That could mean that the system cannot keep your quarters as warm as your thermostat setting calls for.

Fixes

  • These coils have closely spaced metal fins that often become logged with dirt. So have a pro clean these with forced air or steam in extreme cases.
  • Or, try vacuuming the coils with a household hose and brush sweeper. Be careful not to bend the fins though, as they’re delicate. Bending them too much can forever restrict airflow and thus, reduce how well your heating system (heat pump) heats your house.



Extremely Cold Temps Outside Often Cause Honeywell Thermostat Not Heating Up your House Inside

Problem

It’s common for furnaces to fail to keep up when the weather outside is very chilly.  They might run constantly yet still fail to keep up. Now there may be nothing wrong with the thermostat per se. And, there might be nothing the matter with the furnace either. The issue might be that your central heating system is too small to overcome the entering cold from outside.

Fixes

  • Close all windows and drapes, especially during the night.
  • If you have a multi stage heating system, check that all heating stages are working as they should.
  • If your windows are old or are single-pane, try upgrading to at least double-pane. We like triple-pane.  Why?  Because these offer greater insulating. Thus, they keep the heat inside better.

One Stage Not Working in Multistage Systems

Problem

You may be getting SOME heating, but not enough to hold room temperature at the desired value.

Fixes

If you see the Honeywell thermostat not heating up the home, check that your compressors are working.

Check all the heating stages in the furnace (burners, elements), as some have more than one. For multi stage heating, stage one should come on first. As soon as room temperature falls below the set point by half a degree or so, you should hear it start up. If it does not, find out why. Then, the second stage should kick in if the room temp hits two or three degrees less than set temperature. Again, if it does not, this may be what’s causing your Honeywell thermostat not heating up your living quarters.



For heat pump systems, a faulty or badly wired changeover valve may also cause weak heating. In this case, your HVAC system may deliver chilled air though the thermostat is really calling for heat.

Too Little Insulation or Too Much Outside Air Getting In

Problem

If your house lacks enough insulation, this worsens the Honeywell thermostat not heating up issue. Indeed, much warmth leaves through cracks around windows, walls, and doors. Thus, the furnace works harder to bring the house up to the set temperature. Indeed, there may be many BTUs leaking in in this way. So many BTUs, that the central heating system cannot backfill. The furnace cannot thus, maintain the set temperature. So, your thermostat never reaches that set heating temperature.

Fixes

Find the most leaky areas of your home. Do that by walking around inside the house, feeling for cold spots. Look for places where chilly air leaks in. Then, seal these spots with the calking, hardening foams, and other materials.

Be sure that the louvers on any exhaust fans to the outside that you have, close completely when the fan is off.  These include bathroom or kitchen exhaust fans.

Replace faulty windows and doors. Again, single pane windows are huge energy hogs. We suggest replacing these with at least double pane models.

Also, remember the basement. We’ve found that replacing our old single pane basement windows with glass block units helped a lot. See our  How to Install Glass Block Windows post for details on that project.

These new windows took a big load off of our HVAC unit. Indeed, the set temperature grew much easier to maintain over a wide range of heating values. Basement glass block windows, in our case indeed lessened our Honeywell thermostat not heating up problem.




Conclusion

As should be clear, the Honeywell thermostat not heating up problem in homes has many causes. Plus, most of them lie beyond the thermostat. A poorly insulated home, a furnace that’s too small, leaky windows and doors also contribute. All of these make the HVAC system work too hard to heat your home. In many homes there’s little coolness to spare due to poor HVAC sizing. Sadly, the fix for this often costs a lot. Why? Because it means replacing windows and doors, or adding more insulation. Or you may need to upgrade your furnace or add more supplemental heaters to your home.

But we hope that now, you know what might cause the Honeywell thermostat not heating up your home issue. Knowing the causes often helps in choosing the right fixes. Even though the best fix may cost the most, at least now, you have the data in front of you. Good luck, and choose the fixes wisely.

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References

Revision History

  • 2018-05-28: First published.