Home/No heat or no cooling
Guide
HVAC emergency: no heat or no cooling
Safety first, what to check before you call, and what to tell the company – in plain English.
The short answer
If you smell gas, a carbon monoxide alarm sounds or you see smoke, get everyone outside first and call 911 or your gas utility from outside. For anything else, check the thermostat, the air filter and the breaker, then call a company that says it takes emergency calls.
What can wait, and what cannot
Gas, smoke or a CO alarm
- A carbon monoxide alarm is sounding, or anyone has a headache, dizziness or nausea that eases when they step outside
- You smell gas – often like rotten eggs – near a furnace, water heater or stove
- Smoke, or a hot burning smell, from a furnace or other equipment
First: get everyone, pets included, out into fresh air. Do not switch lights or appliances on or off. From outside, call 911 or your gas utility’s emergency number. Do not go back in until you are told it is safe, then have the equipment checked before you use it again.
No heat or no cooling, and it matters
- No heat in freezing weather
- No cooling in dangerous heat, especially with babies, older adults or anyone unwell at home
- Water leaking from a furnace or air handler onto a ceiling or floor
- A breaker that trips again every time the equipment starts
First: turn the equipment off at the thermostat if it is leaking or tripping the breaker, and call a company that says it takes emergency calls. If it is dangerously cold or hot, go somewhere safe until it is fixed.
Fix it soon
- Air that blows but is not heating or cooling well
- Ice on the outdoor unit or on the pipe running to it
- A system that turns on and off every few minutes
- Loud banging, grinding or squealing
First: check the thermostat setting and batteries, the air filter and the breaker. If the system has iced up, turn it off and let it thaw. Then call during business hours.
It can wait for a quote
- A yearly tune-up before heating or cooling season
- An older system that still works, and you want to plan the replacement
- Adding a heat pump or a mini-split
- Hot or cold rooms, or ductwork changes
Do: get two or three written quotes. How to compare them.
Check these first (two minutes)
- The thermostat. Is it on the right mode (heat or cool) and set past the room temperature? Replace the batteries if the screen is blank or dim.
- The air filter. A clogged filter can stop airflow and make a system overheat or ice up. If it is dirty, replace it.
- The breaker and the switch. Check the breaker for the system and the power switch near the indoor unit, which can be mistaken for a light switch. Reset a tripped breaker once. If it trips again, leave it off and call.
- Vents and outdoor equipment. Make sure supply vents are open and furniture is not blocking them. Keep snow, leaves and debris away from the outdoor unit and from any furnace intake and exhaust pipes that run through a wall.
Common situations
No heat
After the checks above, listen for the furnace trying to start. A furnace that clicks but does not light, or lights and shuts off, usually needs a technician – see furnace not working for the full checklist. If you have a gas furnace and smell gas, leave first. In freezing weather, keep faucets on exterior walls dripping and open cabinet doors under sinks to help prevent frozen pipes while you wait.
No cooling, or warm air from the vents
Check that the outdoor unit is running and its fan is spinning, and that the filter is clean. Ice on the indoor coil or on the thick copper pipe is a sign to turn the system off and let it thaw. Do not keep running it. The AC not cooling checklist walks through ten checks.
Water leaking from the system
A clogged condensate drain is a common cause. Turn the system off at the thermostat to stop more water forming, and put a pan or towels down. Water near electrical equipment is a reason to switch off the power to the unit at the breaker and call.
Strange noises or smells
Banging, screeching or grinding means something is failing – turn the system off and call. A burning smell, or any smoke, means switch the system off and, if it continues, leave and call 911.
A carbon monoxide alarm sounds
Get everyone outside into fresh air and call 911 or your fire department from outside. Carbon monoxide has no smell. Do not go back in until it is cleared, and have the heating equipment checked before you use it again.
Before the technician arrives
- Ask on the phone about trip fees and after-hours rates.
- Clear a path to the indoor and outdoor equipment.
- Ask for the license number where your state requires one – your state page links to the lookup.
- Ask for a written price before work beyond the emergency repair starts, and be wary of being told a whole system must be replaced on the spot – get a second opinion if it is not an emergency.
Find a company that takes emergency calls
Every city page has a filter for companies whose own website says they offer 24/7 emergency service. Call to confirm before you rely on it.
Questions
My AC is frozen over. Should I keep running it?
No. Turn the cooling off at the thermostat. You can switch the fan to “on” to help the ice melt, which can take a few hours. Running a frozen system can damage the compressor. A dirty filter or low refrigerant is a common cause, so if it freezes again, call a company.
Is it safe to use a space heater while the furnace is down?
Only a heater made for indoor use, with tip-over protection, plugged straight into a wall outlet, on a hard floor and well away from anything that burns. Never heat a home with a stove, an oven, a grill or a generator running indoors or in a garage – they can fill the home with carbon monoxide.
What should I tell the company on the phone?
What is happening, which part of the system (indoor unit, outdoor unit, thermostat), when it started, any error code or noise, and whether anything smells or leaks. Ask about the trip fee and after-hours rate before they set out.
Why does my furnace smell the first time I turn it on for the season?
A short, dusty burning smell is common as dust burns off the heating parts. If it lasts more than a few minutes, or you smell gas or anything like rotten eggs, leave and call your gas utility from outside.
Where should a carbon monoxide alarm be?
On every level of the home and near sleeping areas, following the manufacturer’s instructions. Test it regularly and replace it when it reaches its end-of-life date. An alarm that sounds is a reason to get everyone outside, not to silence it and carry on.
General guidance for homeowners, not professional or safety advice. When in doubt about gas, carbon monoxide, electricity or anyone’s safety, call 911.