When to call an HVAC pro (and what you can do first)

Leave, or call right now

• You smell gas or rotten eggs, or hear hissing or blowing near a gas line or the meter.The American Gas Association says utilities add mercaptan to natural gas so leaks smell like rotten eggs. DTE Energy lists a burnt-match odor and a hissing sound as leak signs too. A spark from a switch or phone can ignite leaking gas.
  Leave the building now and take everyone with you. Don't flip switches, use appliances or use a phone inside. Call 911 or your gas utility once you're well away from the house.
• A carbon monoxide alarm is going off.The CPSC says to get outside to fresh air immediately and then call 911 if you suspect CO poisoning. Trane gives the same instruction for a CO detector going off.
  Get everyone outside, then call 911. Don't go back in until responders say it's safe.
• People in the house have headaches, dizziness, weakness, nausea, chest pain or confusion, especially when the heat is running.The CDC lists these as carbon monoxide symptoms and describes them as flu-like. The CPSC says more than 200 people in the United States die every year from accidental non-fire related CO poisoning.
  Get everyone outside to fresh air, then call 911.
• A burning, metallic or chemical smell from the furnace, or soot around the furnace or its vents.Lennox lists these among the signs of a cracked heat exchanger, and Carrier warns a cracked heat exchanger can leak carbon monoxide.
  Shut off the furnace, ventilate the house, and call an HVAC technician. If a CO alarm sounds or anyone feels sick, get outside and call 911.
• A burning or musty smell when the AC runs.Trane's advice for burning or musty smells from an air conditioner is to turn off your system and contact an HVAC professional immediately.
  Set the thermostat to Off and call an HVAC technician.
• The furnace vent pipe outside is blocked by snow, leaves or a nest.Trane warns a blocked flue creates a risk of CO poisoning. Bryant says not to attempt to repair or modify furnace venting yourself.
  Turn the furnace off and call an HVAC technician. If a CO alarm sounds, get outside and call 911.

Call a HVAC technician soon

• Hissing, oily residue near the AC or heat pump lines, or ice that keeps coming back after you change the filter and open the vents.Trane, Lennox and Carrier all point to low refrigerant or a leak. Only EPA Section 608 certified technicians can buy refrigerant for home AC and heat pump systems, and releasing refrigerant while servicing a system is prohibited. Lennox says homeowners should not handle refrigerant.
  A licensed HVAC technician with EPA Section 608 certification.
• The outdoor unit hums or clicks but the fan won't spin, or stays silent with the power on.Lennox lists the capacitor and fan motor among the causes. These parts hold and carry high voltage, and Trane says servicing an AC can be dangerous.
  A licensed HVAC technician.
• The furnace clicks over and over but never lights, or lights and goes right out.Trane lists the igniter and flame sensor as likely causes and says you should not attempt to clean or replace the flame sensor yourself.
  A licensed HVAC technician.
• A breaker for the AC, furnace or heat pump trips again after one reset.HVAC.com says not to try turning the system on again, and Lennox says a breaker that re-trips points to an overloaded circuit.
  A licensed HVAC technician.
• The furnace keeps short cycling with a clean filter and open vents, or you see rust or corrosion on it.Bryant says it's not recommended to leave a short cycling furnace running. Lennox lists frequent short cycling and rust among the signs of a cracked heat exchanger. Trane gives 7 minutes as the minimum normal cycle length.
  A licensed HVAC technician. Turn the heat off until they've checked it.
• The condensate drain keeps clogging, the drain pan is cracked or rusted through, or there's water damage.Lennox says recurring clogs, extensive water damage or a clog you can't reach are signs to call a professional. Trane lists a cracked or corroded drain pan as a leak cause.
  A licensed HVAC technician.
• Your fuel-burning furnace or boiler hasn't been inspected in the last year.The CPSC recommends a yearly professional inspection of all fuel-burning home heating systems, including furnaces, boilers, chimneys, flues and vents.
  A licensed HVAC technician, for a routine inspection.

Safe to try first

• Replace the air filter. Trane and Carrier recommend every 1 to 3 months; Bryant suggests checking it monthly and replacing it every 30 to 90 days.
• Check the thermostat settings: Cool or Heat as needed, fan on Auto, and for cooling, at least 3 to 5 degrees below room temperature, as Lennox suggests.
• Replace thermostat batteries with fresh alkaline batteries of the same brand, as Honeywell recommends. Trane suggests doing it yearly.
• Open closed supply vents, clear furniture and rugs off vents and return grilles, and keep interior doors open, as Energy.gov advises.
• With the power off at the disconnect, clear leaves, grass and snow from around the outdoor unit and keep plants about 2 feet away, per Trane.
• Clear a clogged condensate drain with a wet/dry vac at the outdoor end and diluted vinegar at the indoor access point, as Lennox and Carrier describe. Turn the AC off first.
• Thaw a frozen AC by switching from Cool to Off and running the fan on On. Carrier and Lennox both suggest it. Never chip at the ice.
• Reset a tripped breaker once, opening only the hinged panel door, never the metal cover behind it. If it trips again, leave it off and call a technician.

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