No Heat During a Texas Freeze? What to Do (San Antonio)

Updated September 2026 · HVAC Flow Solutions

If your heater will not turn on during a San Antonio cold snap, run through six quick checks first: thermostat on Heat with fresh batteries, the furnace power switch and breaker, the air filter, the ignition on gas furnaces, the defrost cycle on heat pumps, and open vents. Most no-heat calls trace back to one of those. This guide walks you through each check, the safety rules that matter when the temperature drops, how to protect your pipes, and when to stop and get a pro out.

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Check these 6 things, in this order

Thermostat. Set it to Heat, not Cool or Fan, and raise the setpoint 3 to 4 degrees above room temperature. Swap the batteries. After months of not using heat, the mode switch and dead batteries are the two most common culprits.
Furnace switch and breaker. Most furnaces have a wall switch nearby that looks exactly like a light switch, and people flip it off without realizing. Check it, then check the breaker panel for anything labeled furnace, heat, or air handler. Reset a tripped breaker once. If it trips again, stop and call.
Air filter. A clogged filter chokes airflow, the furnace overheats, and a safety switch shuts the burners off. That is the classic reason a furnace blows cold air or short cycles. If you cannot see light through the filter, replace it.
Gas furnace ignition. Newer furnaces flash a status light with an error code behind a small window on the unit. Note the blink pattern for the technician. On older furnaces the pilot light may be out. If you are not comfortable relighting it, do not force it. And if you ever smell gas, leave the house and call CPS Energy before anything else.
Heat pump ice check. Light frost and occasional steam from the outdoor unit is normal defrost mode. A unit frozen into a solid block of ice is not. If it is iced solid or the house keeps getting colder, switch the thermostat to Emergency Heat so the backup strips carry the house, and book a pro.
Vents and returns. Make sure supply vents are open and return grilles are not blocked by furniture, rugs, or holiday storage. Closed vents in unused rooms raise pressure and can trip the same safety shutoffs as a dirty filter.

Safety first, always: never heat your home with a gas oven, grill, or camp stove, and never run a generator indoors or in the garage. Carbon monoxide from those choices kills people in Texas every freeze. Keep space heaters 3 feet from anything that burns, plugged straight into the wall, never a power strip. If you smell gas, leave first and call from outside.

Why San Antonio homes struggle when it freezes

Our houses are built for 100° summers, not 20° nights. Insulation is thinner than up north, pipes run through exterior walls and attics, and many homes heat with heat pumps that lose efficiency exactly when the temperature plunges. Add a furnace that has sat unused for nine months, and the first hard front of the year becomes the moment weak parts give up. The 2021 winter storm proved how fast it happens: heating systems across the city failed in the first 24 hours, and every repair company's phone lit up at once. The homeowners who got help first were the ones who called early.

Protect your pipes while you wait

If the heat is out during a freeze, your pipes are the second emergency. Let faucets on exterior walls drip, open the cabinet doors under sinks so room air reaches the plumbing, cover outdoor faucets, and find your main water shutoff now, before a burst pipe makes you search for it in the dark. A dripping faucet costs pennies. A burst pipe costs thousands.

Beat the rush: prep before the front arrives

Cold fronts in Texas are forecast days ahead, and the smartest time to find a heating problem is before everyone else finds theirs. When a front is coming:

Test your heat today. Run it for 15 minutes and make sure warm air reaches every room. A dusty smell in the first hour of the season is normal and fades.
Replace the filter so airflow is not the thing that shuts you down on the coldest night.
Cover outdoor faucets and locate your water shutoff while it is still comfortable outside.
Book the repair early. If the test run shows a problem, getting a pro out before the freeze means choosing among available companies instead of joining a city-wide queue.

Get your heat handled before the next front

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Frequently asked questions

Why is my furnace blowing cold air?

First check that the thermostat fan is set to Auto, not On. On the On setting the blower runs between heating cycles and pushes unheated air. Other common causes are a clogged filter overheating the furnace so it shuts the burners off, or a failed ignition. If switching to Auto and replacing the filter does not fix it, call a pro.

Is it normal to smell burning when I first turn on the heat?

A dusty burning smell for the first hour of the season is usually just dust burning off the heat exchanger after months of sitting unused. It should fade quickly. A persistent burning smell, an electrical smell, or any gas smell is not normal. Turn the system off and call. If you smell gas, leave the house first.

Should I switch my heat pump to Emergency Heat?

Only if the heat pump itself has failed or is frozen into a solid block of ice. Emergency Heat runs electric backup strips that cost far more to run. Light frost on the outdoor unit with occasional steam is normal defrost mode, not a failure. If the unit is solid ice or the house keeps getting colder, switch to Emergency Heat and call a pro.

How do I keep my pipes from freezing in San Antonio?

Let faucets on exterior walls drip, open cabinet doors under sinks so warm air reaches the pipes, cover outdoor faucets, and know where your main water shutoff is before you need it. San Antonio homes are built for heat, not hard freezes, so exposed pipes ice up faster here than the temperature alone suggests.

Not sure who to call when you need the work done? See how to choose an HVAC contractor in San Antonio, or get a feel for pricing with our repair cost guide. Summer trouble instead? Start with why is my AC not cooling.

This guide is for general information and reflects HVAC practices in the San Antonio, Texas area. In any emergency involving gas or carbon monoxide, leave the home and call 911 or CPS Energy first. Last updated September 2026.