Informational Guide

Heater Won't Turn On But AC Works (Causes & Solution)

Having a heater that doesn’t work but an AC that does can be frustrating. Learn all about the causes and solution to this HVAC problem.

by Josh M

Is your heater not producing heat or producing it inconsistently, but your AC pumps out cold air without a problem? The situation isn’t just chilly but also frustrating.

Fortunately, when your AC works but not heat, several solutions are available. Read on to learn how to get your entire HVAC system working quickly and correctly.

Faulty Thermostat

Thermostats can be fairly sensitive, especially the older analog type. If your heater turns on and off inconsistently, heats your home unevenly, or doesn’t work at all, a faulty thermostat might be to blame.

Check the thermostat carefully for signs of damage. Also, make sure it’s level on the wall.

Note the thermostat’s placement in the home. Is it exposed to direct sunlight throughout the day? Is it near a draft? Extremes can impair the thermostat’s ability to read the temperature.

Related ArticleHow To Reset An AC Thermostat

Honeywell thermostat wall

Clogged Filters and Ductwork

Clogged furnace filters and interior ductwork can impair or stop your home’s heating system. Dust is the most likely culprit. It typically builds up the fastest during the winter months, especially in homes with poor ventilation.

The EPA recommends duct cleaning to help improve function. While no official cleaning guidelines exist, you’ll want to have ducts cleaned more frequently if you own pets, live in an older house, or suffer from allergies.

Check your air filters often. Replace when they’re dirty. At a minimum, replace your air filters every three months, but monthly is ideal.

Pilot Light

Gas and propane-powered furnaces can fail if the pilot light goes out. To reset the furnace, you’ll first need to turn off the electrical component and breakers. Then open the front access panel.

The pilot light is a metal tube running from the gas value into the furnace. When working correctly, it should have a small flame. Relighting it requires either pressing the priming button or lighting it manually with a long lighter (this is relatively rare).

Never light your pilot light if you smell or hear gas. The valve on your pilot light is likely damaged.

Poorly Maintained Furnace

A consistent lack of basic maintenance can lead to various mechanical problems, including the heat going out but the AC working properly. Without proper upkeep, common issues that can occur include:

  • Motor slowdown or stoppage
  • Excess stress on components
  • Overall reduced lifespan

An annual or semi-annual professional furnace inspection is the best way to prevent major problems with both the heating and cooling elements. A standard furnace inspection includes cleaning, lubrication, connection tightening, and measurements.

Central Air Not Working But Heat Is: Causes Explained

If the heat works but not the AC, there are several potential causes.

Lack of Power

A problem with the power supply is one of the most common reasons why an AC unit won’t turn on at all. Check your home’s breaker box for a tripped fuse. Getting the AC running could be as simple as flipping a switch.

Damaged Vents

As with heat, damaged ductwork can stop your AC system from blowing out cold air. If the ventilation system has leaks, holes, or tears, you’ll likely notice inconsistent temperature levels throughout your house.

Damaged vents should be replaced or repaired as soon as possible, as they’ll result in not just inconsistent temperatures but also high utility bills. The best option is hiring an HVAC professional.

Leaks

An air conditioning systems works by removing heat and moisture from the air, which cools its temperature. As part of this process, the system uses a drain line to direct water into a pan.

If the line becomes damaged or moves out of position, the system won’t cool the air properly. Even worse, water can leak from the AC throughout your home. Contact HVAC professionals at the first sign of water leakages, such as unexplained pools and stains on the ceiling.

A less obvious scenario could include a refrigerant leak. You will need a licensed HVAC specialist to test for this.

Central Heat & Air Conditioner Both Not Working: What To Do?

If both your central heat and air are not working, a few potential issues might be occurring system-wide. Here’s how to identify and treat the most common reasons why both the heat and AC have stopped.

Central Air Conditioner Condenser Unit Mounted on a Wall
Check the Power

Power issues will result in both the heat and AC failing to work. Check your home’s circuit panel to make sure it hasn’t flipped a breaker or blown a fuse.

Check the Thermostat

Make sure the thermostat is level against the wall and out of direct sunlight. Set it at least three degrees either above or below your home’s current temperature. If the system fails to turn on, you might need a new thermostat.

Check the Ventilation System

If both your heating and AC turn on but aren’t changing the temperature in your house as efficiently as you’d expect, check your ventilation system. If the external vents are open and unobstructed, the problem might be inside the ventilation system, requiring either cleaning or replacement.

People Also Ask (FAQ)

Why is my heat blowing cold air in my house?

Common HVAC system problems that result in the heater blowing cold air include:

  • Damaged blower motor
  • Faulty fan switch
  • Low refrigerant levels

These issues require mechanical repair, meaning they’re usually best handled by a technician.

How do I get my heat to kick on?

If your heat won’t turn on, the first step is to raise the thermostat by at least three degrees. Also, check your vents for both internal and external obstructions. Finally, check the pilot light.

Can I reset the central heating system if it’s not working?

Rebooting your home thermostat will sometimes get it to start working. Turn the thermostat two degrees below room temperature (keep it set to Heat, not Cool). You’ll hear a click.

After you hear the click, go to your breaker box, where you’ll reset your furnace. Wait about 30 seconds between flipping the switch off and on. Finally, set your thermostat a few degrees higher than your house.

How many times can I hit the reset button?

Be careful! Pressing the reset button more than two times is dangerous. Each button press forces more oil into the chamber.

If the furnace lights when too much oil is present, an explosion can occur.

Conclusion

If the AC works but not the heat, several solutions are available. First, check the obvious, such as the thermostat settings and vent clearance. Then, check for mechanical issues, such as a slowed fan or unlit pilot light.

With routine maintenance and regular inspection from an HVAC professional, you can enjoy both hot and cold air year-round.

Last Updated on May 26, 2022

Josh M

My name is Josh and I am obsessed with the HVAC industry. I created this website to help HVAC techs of all levels get the best out of their heating & cooling systems. I have spent thousands of hours studying air conditioners, heaters and home air products so you can learn & buy with confidence. Learn more about the team here.

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