You might see your Honeywell thermostat that says that the heat is on, and yet you get no heat. This can happen for many reasons. A broken thermostat, incorrect wiring, tripped circuit breakers, blown fuses, or a broken HVAC system could cause this. Here, we describe some of these causes, and then offer troubleshooting techniques and repair hints to solve them. First, we look at what might go wrong in the thermostat itself. Then we talk about the power and appliance issues that can also cause this.
Why the Honeywell Thermostat Says Heat On but No Heat
1. Thermostat Badly Wired
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 heat. Other symptoms may arise too. These depend on which wires and how many of them you have connected to the wrong thermostat terminals.
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.
2. Broken Thermostat Wiring
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 heat operation.
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.
3. Thermostat Temperature Set Too High or Too Low
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. On particularly cold days, it may feel like there’s no heat output, even though the furnace is operating normally.
- 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 heat 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 highest indoor temperature that your furnace can reach.
Honeywell Thermostat Says Heat On but No Heat: Furnace Issues
1. Clogged Furnace Filters and Fan Blades
Dirty air filters can constrict airflow though the furnace’s heat exchanger, and cut the heat output to near zero. 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.
- Replace 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 and inspect the control units for damage. Plus, he should clean out air ducts, check heat registers for clogs, and so on.
2. Wrongly Sized or Worn Heat System can Cause
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 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. In this case, the unit will produce little or no heat even though it’s running.
- Have an HVAC tech check refrigerant pressure. If it is low, fill with enough refrigerant to bring this reading into spec. 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 not too old. But if it is older than a couple decades, then replace the whole system.
3. Dirty or Frosted Heat Pump Coils can Trigger the Honeywell Thermostat Says Heat On but No Heat Issue
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.
- 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. Thus you reduce how well your HVAC heats your house.
4. Extremely Cold Temps Outside Often Cause the Honeywell Thermostat Says Heat On but No Heat 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. Again, a very cold day can make it feel inside like there’s no heat.
- 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.
5. One Stage Not Working in Multistage Systems
You may be getting SOME heating, but not enough to hold room temperature at the desired value.
- 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, the furnace should start. But 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.
6. Too Little Insulation or Too Much Outside Air Getting In.
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.
- 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 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.