Hands sliding a new pleated air filter into the filter slot of a furnace
A clean filter is the first fix for weak airflow and short cycling.
Heating & cooling

HVAC maintenance and fixes to try before you call

When the house is too hot or too cold, start with the basics. A dirty filter, a tripped breaker or a thermostat setting explains a lot of heating and cooling problems. These guides cover the checks for furnaces, air conditioners, radiators and water heaters, and the signs that it's time to call for service.

  • 24 fixes
  • Step-by-step pictures
  • When to call a pro

Where to start: The single most useful habit is changing the air filter on schedule. If the heat won't come on, run through the five furnace checks, and if a radiator is cold at the top, bleed out the air. If the AC runs but the air isn't cold, work through the AC checklist, and give the outdoor unit a spring coil cleaning. Electric water heater gone cold? Try the hidden reset button.

Outdoor AC condenser with dirt packed into the coil fins, the fan on top, the disconnect box, and a fin comb
From the guide: Clean your AC condenser coils →

Water heater trouble, like no hot water or a noisy tank, is in Plumbing.

No heat? Start hereA step-by-step checklist for a home with no heat: gas smell, thermostat, does it start, is the air warm, does it shut off early, with a repair guide for each answer.No heat? Start hereAnswer each question in order.1Smell gas or rotten eggs?YESSAFETY FIRSTLeave the house nowDon't flip switches or touch the thermostat.Call the gas company or 911 from outside.No, keep going2Thermostat on Heat, set aboveroom temp, screen working?NOMOST COMMON FIXFix the thermostatSet it to Heat, raise the temperature,swap the batteries.Thermostat not working →Yes, keep going3Does the furnace or heat pumpstart up?NOCHECK THE POWERBreaker and furnace switchLook for a tripped breaker, the furnacepower switch and the blower door.Furnace not turning on →Yes, keep going4Is the air from the ventswarm?NO, COLDDo you have a heat pump?YESLIKELY CAUSEDefrost cycle or low chargeDefrost is normal and passesin a few minutes.Heat pump blowing cold air →NOLIKELY CAUSEFan setting or ignitionSet the fan to Auto, then checkthe filter and flame sensor.Furnace blowing cold air →Yes, keep going5Does it shut off after only afew minutes?YESLIKELY CAUSEShort cyclingUsually a dirty filter, a dirty flamesensor or a badly placed thermostat.Furnace short cycling →No, keep goingSTILL CHILLY?Weak airflowA clogged filter starves the wholehouse. Change it first.Change your air filter →
No heat? Answer each question in order and follow the link to the matching repair guide. Open full size

What are you dealing with?

House feels dusty, bills are upAC blowing warm airFurnace won't turn onRadiator cold at the topElectric water heater stopped heatingOutdoor AC unit is dirtyThermostat is blank or not workingWater leaking around the AC or furnaceOne room is too hot or coldBurning smell when the heat comes onIce on the AC linesFurnace turns on and off a lotHeat is on but vents blow coldBaseboard heater stays coldHeat pump blows cool air in winterFurnace is making noise
Heating & cooling

How to replace a furnace humidifier pad

 Easy30 min–1 hr$15–$40
Heating & cooling

Fireplace smoking into the room

 Easy15 min–1 hr$0–$40
Heating & cooling

Humidifier not working or not putting out mist

 Easy20 min–2 hr$0–$20
Heating & cooling

Space heater keeps shutting off

 Easy15–45 min$0
Heating & cooling

AC vents sweating or dripping water

 Easy30–90 min$5–25
Heating & cooling

Heat pump frozen in winter

 Easy30–90 min, plus thaw time$0–30
Heating & cooling

Dehumidifier not collecting water

 Easy15–60 min, plus thaw time$0–20
Heating & cooling

Window AC leaking water inside

 Moderate30–90 min$0–20
Heating & cooling

Change your HVAC air filter

 Easy5 min$8–30
Heating & cooling

AC not cooling? Check these first

 Easy20–45 min$0–30
Heating & cooling

Furnace won't turn on

 Easy15–30 min$0–30
Heating & cooling

Bleed a radiator

 Easy10 min per radiator$2–5
Heating & cooling

Reset an electric water heater

 Moderate15–20 min$0
Heating & cooling

Clean your AC condenser coils

 Easy45–60 min$15–30
Heating & cooling

Thermostat not working or blank

 Easy15–30 min$0–10
Heating & cooling

Water leaking from the AC: clear a clogged condensate drain

 Easy20–40 min$0–15
Heating & cooling

One room too hot or too cold

 Easy30–60 min$0–20
Heating & cooling

Burning smell when the heat comes on

 Easy15–60 min$0–20
Heating & cooling

Ice on the AC lines or coil

 Easy3–24 hours to thaw, 20 min of work$0–20
Heating & cooling

Furnace turns on and off too often

 Moderate30–60 min$0–20
Heating & cooling

Furnace blowing cold air

 Easy15–60 min$0–40
Heating & cooling

Electric baseboard heater not working

 Moderate20–60 min$0–50
Heating & cooling

Heat pump blowing cold air

 Easy15–45 min$0–40
Heating & cooling

Furnace making noise

 Moderate15–60 min$0–30

Common questions

How often should I change my furnace filter?

Every 1 to 3 months for standard 1-inch filters. Check it monthly if you have pets, allergies or construction dust.

When should I call an HVAC technician?

If you smell gas, the unit trips the breaker again after a reset, or the free checks don't help. Refrigerant, gas valves and electrical parts inside the unit are jobs for a pro.

Looking for something else? Browse all fixes or see emergency steps.