honeywell thermostat says heat on but no heat

A common issue that often arises on analog and digital Honeywell Thermostats is Honeywell thermostat says heat on but no heat.

A Honeywell thermostat has a very critical job in a household; it’s the brains of the heating and air conditioning system, telling it what temperature to keep inside your home.

There are at least four main possible reasons why your Honeywell flashes heat on with no heating; wiring faults, clogged blades and filters, setting extremely high temperatures, faulty furnace parts.

It’s essential to tackle these issues separately to get to the root cause since they all have different solutions.

Don’t let the faults discourage you, even if you’re not an expert with Honeywell Thermostats or HVAC systems. Like most electronics in your household, you can quickly fix the problem in a few minutes.

Reasons Why There’s No Heat, but Honeywell Thermostat Flashes Heat On

When there is no heat but it indicates “heat on”, the first step to troubleshooting a problem is figuring out what’s wrong.

Older Honeywell thermostat models are usually analog kind and display minimal features. They cannot be programmed like their digital counterparts. They’re easier to troubleshoot and fix with few simple adjustments.

Here are some additional issues that may make your Honeywell Thermostat say Heat on but no heat:

Sensor Not Working

If there is no physical problem with the thermostat, it’s possible that the sensor isn’t working and, therefore, not relaying the correct temperature.

Sensors have a life expectancy of five to ten years and replacing them is pretty expensive compared to other parts of the Honeywell Thermostat.

Low Battery

Some homes have thermostats that run on batteries. If you’re having problems with your analog thermostat yet it has been working perfectly all along, try replacing the batteries.

It is worth changing your thermostat’s batteries periodically, even if you don’t get the “replace bat” message.

Honeywell Thermostat Says Heat On But No Heat – Solutions

fix honeywell thermostat heat

Solution #1 Rewire Honeywell Thermostat

If your Honeywell thermostat flashing heat on but no heat, it’s possible that you wired something wrong, which in turn caused the heating problem.

It would help if you rewired the thermostat before other symptoms started showing up.

Just like other thermostats, Honeywell Thermostats terminals are labeled and identified as per industry standards.

The following is a list of the terminal letters as well as their functions:

Rc – Acts as a switch for the cooling system.

Rh – Acts as a switch for the heating system.

W – For controlling heating.

O – Switches pump back and forth from cool to heat and vice versa.

Y – For controlling cooling and compressor.

C – It’s a return path for the transformer.

G – Controls the fan.

How to Rewire:

You may need to use a pair of needle-nose pliers to make sure the wires are straightened out before connecting them to the new terminals.

Here’s how to rewire the Honeywell thermostat:

Step 1: Connect the cable to the wall terminal, then the other end to the thermostat.

Step 2: Confirm that the wires are appropriately connected to the thermostat with matching color codes.

Step 3: At the furnace end, ensure that the cables are also connected with matching color codes.

Solution #2 Clean Clogged Fan Blades and Filters

The dirt that accumulates on the walls of your furnace or fan blades should be a cause for alarm.

It can waste fuel/electricity and drastically lower the efficiency of your HVAC system.

A clogged filter can make it harder for the HVAC furnace to heat your home. The three major parts of the furnace, the filter system, the blower, and the motor, are prone to clogging, primarily when used frequently.

You’ll need a screwdriver, clean rags, replacement filter, vacuum cleaner and a toothbrush.

Here’s how to clean the clogged furnace parts:

  1. Remove the outside panel of your furnace or air conditioner to access the blower or to get to the front of the furnace.
  2. Use a screwdriver to unscrew the fan unit, then slid it out.
  3. Clean out the dirt from the pulleys to the blower, belts, blower assembly and the motor housing.
  4. Use your toothbrush to clean each fan blade and clear any debris between blades.
  5. Clean off all debris and dirt from the inside and outside the motor housing to prevent heat buildup.

It’s best to mark the wire connections before they’re removed from the unit so that you can reattach them correctly later.

Solution #3 Avoid Setting Too High Temperatures

The temperatures you set may be way higher than what your HVAC system can handle and deliver. This is the most common cause of why Honeywell thermostat says heat on but no heat, but it’s easy to solve.

For example, in cold weather, you might set your thermostat to 80 degrees, but your thermostat can only handle 70 degrees.

Here’s how to fix the issue:

  1. Check your furnace and always be aware of its capabilities.
  2. Set up realistic temperatures for your heating system.
  3. If need be, upgrade the heating system to a bigger or more capable unit.

Solution #4 Replace Worn Out Furnace System

Like all home electronic systems, the furnace system has numerous parts that tend to lose efficiency over time.

Some parts are more efficient and last longer than others, but industry experts advise that you make replacements every ten to fifteen years.

In most cases, it starts with refrigerant leaks, then valve leaks which can go on for a long. If not fixed, your HVAC system will certainly not serve the function it’s meant for, even though your Honeywell Thermostat is just fine.

Here’s how to make replacements for worn-out furnace systems:

  1. Check the HVAC refrigerant pressure.
  2. Check the HVAC system specs and ensure the refrigerant pressure matches the specs.
  3. Check the manual or HVAC covering to find the correct values for the head and tail pressures of the compressor unit
  4. Run the compressor the read head and tail pressures.
  5. Replace the compressor if the ratio between head and tail pressures is too low.

Read Next: Why Honeywell Says – Low Battery?


If your Honeywell thermostat heat flashes on with no heat, at the very least, ensure you have set temperatures that your HVAC system can handle. If this doesn’t solve the problem, you’ll have to rewire your thermostat, clean away dirt from your HVAC system or replace worn-out furnace parts.

Most of the Honeywell thermostat says heat on but no heat issues lie beyond the thermostat itself.

Sadly, the cost of fixing the faults can run into hundreds or thousands if you have to replace crucial parts of the furnace. If you’re in extremely cold conditions, you may need to add supplemental heating sources.

Nicole B