Why Is My House Not Heating Up?

Reviewed 2026-08-01 · How we research

Warning signs of not heating up

• Thermostat display is blank or unresponsive
• Furnace makes repeated clicking sounds and then goes silent
• Outdoor heat-pump unit is coated in ice or frost
• Vents blow no air at all, not even cold air
• A gas or oil delivery tank is reading empty

Most likely causes of not heating up, ranked

1. 1. Thermostat set wrong, dead batteries, or miscommunicating

   Most common — the first thing to rule out

   The thermostat has to be set to Heat mode with a setpoint above room temperature, and battery-powered models stop calling for heat entirely when batteries die, sometimes leaving a blank or frozen display. Smart thermostats can also lose their Wi-Fi connection to the equipment and simply stop sending the call for heat.

   10-minute self-test: Confirm the mode says Heat, raise the setpoint 5 degrees above the current room reading, and listen for a click within a minute. If the screen is blank or dim, replace the batteries before doing anything else.

2. 2. Tripped breaker or a furnace power switch left off

   Very common

   Furnaces and heat pumps run on a dedicated circuit breaker, and furnaces also have a wall switch that looks like a light switch near the unit. Either one being off stops the system completely even though the thermostat still shows power.

   10-minute self-test: Check the breaker panel for a breaker in the middle position and switch it fully off, then on. Confirm the furnace's own toggle switch, usually mounted on or near the unit, is in the up/on position.

3. 3. No fuel reaching the furnace or boiler

   Common, especially with propane or oil

   A propane tank running empty, a paid oil delivery that has not arrived, or a natural gas utility shutoff (planned maintenance, unpaid bill, or a safety shutoff after detected leak) all stop combustion heat completely. This is one of the most overlooked causes because the thermostat and blower can still appear to work normally.

   10-minute self-test: Check the propane tank gauge or oil tank sight glass. For natural gas, check whether other gas appliances like a stove or water heater are also working; if none of them work, the gas supply itself is the issue and needs the utility, not a technician.

4. 4. Furnace in safety lockout after failed ignition

   Common in older or poorly maintained furnaces

   Gas furnaces attempt to light a set number of times and then lock out to prevent gas from building up unburned. This is a safety feature, not a malfunction to force past. Causes include a fouled flame sensor, weak igniter, or blocked intake or exhaust vent pipe outside the house.

   10-minute self-test: Turn the thermostat off for 30 seconds, then back on, and listen for one full ignition attempt. If it locks out again, do not keep resetting it — repeated attempts can allow unburned gas to accumulate. Call a technician instead.

   This cause is not a DIY repair — it needs a hvac technician.

5. 5. Frozen or ice-covered heat pump outdoor unit

   Common in freezing, humid weather

   Heat pumps run periodic defrost cycles to clear normal frost, but a coil fully encased in ice means airflow is blocked, a fan motor has failed, or the defrost control board is not cycling correctly. A frozen unit cannot move heat and effectively shuts the system down.

   10-minute self-test: Walk outside and look at the coil fins around the unit. A thin, even frost that disappears within an hour is normal; a solid sheet of ice covering the coil or fan is not and needs a technician.

6. 6. Reversing valve or refrigerant problem in a heat pump

   Less common but produces a total heating failure

   The reversing valve switches a heat pump between cooling and heating modes. If it sticks or the system has lost refrigerant charge, the outdoor unit may run without producing any usable heat indoors. Refrigerant work requires an EPA-certified technician and is not a homeowner task.

   10-minute self-test: Feel the two refrigerant lines running to the outdoor unit while the system is set to heat. If both feel roughly the same temperature instead of one being warm, suspect the reversing valve or charge and call a technician rather than adding refrigerant yourself.

   This cause is not a DIY repair — it needs a hvac technician.

7. 7. Clogged filter starving the blower and tripping a safety switch

   Common and easy to fix

   A filter packed with dust restricts airflow across the heat exchanger, which can overheat and trip a high-limit safety switch that shuts the whole unit down before it produces warm air.

   10-minute self-test: Pull the filter and hold it to a light. If light does not pass through it, replace it and try the thermostat again.

8. 8. Duct disconnection or major leak in an unconditioned space

   Less common but total when it happens

   A duct that has fully separated in an attic, crawlspace, or basement can dump most of the heated air outside the living space, leaving registers blowing weak or no warm air at all even though the furnace runs.

   10-minute self-test: With the system running, go into the attic or crawlspace and listen for rushing air or feel for warm air near duct joints away from any register.

Your 10-minute check list for not heating up

1. Confirm thermostat mode is Heat and the setpoint is above room temperature
2. Check the breaker panel and the furnace's own on/off switch
3. Check propane, oil, or gas supply and whether other gas appliances work
4. Inspect and replace the filter if it is dark or clogged
5. Look at the outdoor heat pump unit for solid ice

What it costs to fix not heating up

See the full cost breakdown for this repair →

DIY fixes for not heating up

• Cycle the thermostat and check batteries

  Replace batteries, confirm heat mode, and raise the setpoint. This resolves a surprising share of true no-heat calls.

• Reset the breaker once

  Switch the breaker fully off, then on. If it trips again immediately, stop and call an electrician or HVAC technician — repeated tripping means a fault, not a fluke.

• Replace the filter

  A new filter takes two minutes and removes one of the most common causes of a safety shutdown.

• Clear snow and debris from the outdoor heat pump unit

  Keep at least 18 inches of clearance around the unit and brush away snow, but do not chip at ice with a hard tool, which can damage the fins.

Mistakes to avoid with not heating up

• Never repeatedly reset a furnace that keeps locking out; that risks unburned gas accumulating
• Never chip ice off a heat pump coil with a metal tool
• Never attempt to add or check refrigerant yourself
• Never re-enter a building after a gas smell or CO alarm until cleared by professionals

Where homeowners waste money on not heating up

• Paying for an emergency after-hours call before checking the breaker and thermostat batteries yourself
• Replacing a whole furnace based on a single lockout without a technician confirming the actual failed part
• Buying a space heater as a long-term fix instead of resolving a fuel-supply or ignition problem

When to call a hvac technician about not heating up

What a hvac technician actually does on this job →

How to prevent not heating up coming back

• Schedule annual furnace or heat pump maintenance before the heating season starts
• Replace filters every 60–90 days
• Keep propane tanks refilled before they run low in winter
• Install a CO detector on every level of the home

Why Is My House Not Heating Up — questions homeowners ask

Sources used for not heating up

• U.S. Department of Energy — Heating Systems
• CPSC — Carbon Monoxide Information Center
• ENERGY STAR — Home Sealing and Insulation
• American Gas Association — natural gas safety
• Carrier — technical resources
• ACCA — HVAC service standards