Heating & Cooling Combined Unit: Why won't my furnace turn on?

Check the thermostat to make sure it's set for heat and the temperature setting is high enough to call for heat. Adjust the thermostat if it isn't set properly.

If you have a digital thermostat and it doesn't light up, check the house circuit breaker for your furnace. Reset the house circuit breaker if it's tripped.

If the thermostat is getting power but won't light up, the thermostat may have failed. Replace the thermostat if it doesn't light up even though it's getting power.

Many furnaces have a power cut-off switch located next to the furnace that shuts off power to the furnace during the off-season. Check that switch to make sure it's turned on.

Other problems that can prevent your furnace from working include: failed interlock switches, exhaust ventilation system problems, wiring failures or control problems. Have a service technician diagnose and repair the furnace failure if you can't fix the problem using basic troubleshooting steps.

heating & cooling combined unit

THESE REPAIRS MAY HELP SOLVE YOUR HEATING & COOLING COMBINED UNIT PROBLEM

Thermostat replacement

Replace the HVAC system thermostat

The thermostat controls the heating and cooling system in your home. The thermostat senses the temperature inside your home and cycles the system on and off to maintain the set temperature. When your HVAC system control thermostat quits working, replace the thermostat.

Hvac system thermostat

Find the required part specific to your product.

HVAC Thermostat
March 3, 2022By Lyle Weischwill

How to replace a heating and air conditioning system thermostat

If the buttons on your HVAC system control thermostat don't work or if the display panel doesn't light up, the thermostat may need to be replaced. This DIY repair guide explains how to replace a thermostat in less than 30 minutes.

Repair difficulty
Time required
 30 minutes or less

Symptoms common to all heating & cooling combined units

Choose a symptom to see related heating and air conditioning system repairs.

Dirty air filter, clogged condenser coils, low refrigerant charge, faulty compressor
Thermostat problem, clogged air filter, burner failure
Dirty flame sensor, failed flame sensor, damaged burner, bad high limit switch
Thermostat problems, bad compressor/condenser fan capacitor, lack of refrigerant, failed compressor
Main causes: errant thermostat settings, lack of electrical power, clogged drain line, wiring failure, control failure.
Main causes: Errant thermostat settings, lack of power, bad interlock switches, lack of exhaust ventilation, wiring failures.

Repair guides common to all heating & cooling combined units

These step-by-step repair guides will help you safely fix what’s broken on your HVAC system.

March 16, 2022
By Sears PartsDirect staff
How to unclog the air conditioner drain line

The condensate drain line for your central air conditioner can clog with mold and mildew. Water will back up and start dripping below the inside air conditioner unit. Follow the steps in this guide to unclog the drain pipe.

Repair difficulty
Time required
 15 minutes or less
March 16, 2022
By Sears PartsDirect staff
How to replace the furnace flame sensor

The flame sensor detects when furnace burner flames are lit. You may need to replace the flame sensor if flames only stay on for a few seconds.

Repair difficulty
Time required
 15 minutes or less
How to replace a heating and air conditioning system thermostat

The control thermostat for your HVAC system can stop working. This repair guide shows how to replace it.

Repair difficulty
Time required
 30 minutes or less

Articles and videos common to all heating & cooling combined units

Use the advice and tips in these articles and videos to get the most out of your HVAC system.

August 5, 2022

Introducing new technical repair content that we’re developing for the Sears Technical Institute

By Sears PartsDirect staff

Learn about Sears Technical Institute and the advanced technical content being developed for aspiring appliance techs.

February 22, 2022

Why is my furnace not igniting?

By Lyle Weischwill

Find out why the burner on your furnace isn't igniting.

February 22, 2022

Can a furnace be repaired?

By Lyle Weischwill

Learn about furnace repairs and how much they cost.