What to Check Before You Call for Service

If you smell gas anywhere in the house, stop and act. Do not flip a switch, do not use a phone inside, do not hunt for the source. Get everyone out including pets, leave the door open behind you, and from outside call 911 and Washington Gas. That rotten egg smell is an odorant added to natural gas so you can detect a leak. Treat it as real every time, even if it fades. If a carbon monoxide alarm sounds, the same rule applies: outside first, then call.

Two other hard limits. Do not open sealed equipment. The burner compartment of a furnace, the electrical cabinet on an outdoor unit, and anything containing refrigerant are not homeowner territory, and an outdoor unit holds a capacitor that can store a dangerous charge long after the power is off. And do not touch wiring. Everything below can be checked with the power off, a flashlight and your hands. Past that line, a call is the right answer.

Look at the thermostat first, because this is the most common reason a no heat or no cool call turns out to be nothing. Confirm the mode: COOL in July, HEAT in January, not OFF. Confirm the setpoint is actually calling for something, meaning several degrees below room temperature for cooling or above it for heating. Confirm the fan is set to AUTO. A fan left on ON blows room temperature air and convinces people the system is running when it is not.

If the screen is blank, dim, or showing a low battery icon, change the batteries. Most models take two AA or AAA cells behind a faceplate that pulls straight off the wall plate. Do it even if it seems unlikely, because dying batteries produce strange behavior well before they produce a blank screen: a system that runs and will not shut off, or one that ignores its own schedule. Check the date and time too, since a wrong clock runs the wrong program.

Go to the electrical panel and find the breakers for the furnace or air handler and for the outdoor unit. They are usually labeled. A tripped breaker often does not look obviously off. It sits slightly out of line with its neighbors. To reset one, push it firmly to OFF until it clicks, then back to ON. If it trips again immediately, stop. A breaker that will not hold is telling you something is wrong downstream, and resetting it repeatedly is not safe.

Then look for the service switch. It is an ordinary looking light switch, usually on or beside the furnace or air handler, at the top of the basement stairs, or right outside the attic access. Painters, cleaners and anyone hunting for a basement light flip it by mistake, and it cuts all power to the equipment. There is often a matching disconnect in a small metal box next to the outdoor unit. Check both.

On the gas side, the shutoff valve in the pipe feeding the furnace, boiler or water heater should have its handle parallel to the pipe, which means open. Perpendicular means closed. On older equipment with a standing pilot, a small flame that stays lit all year, look through the sight window and see whether it is burning. Relighting instructions are printed on a label on the unit. Follow it exactly, and if the pilot will not stay lit after one try, stop and call.

Pull the filter out. If it is gray and packed, that alone explains weak airflow, a frozen indoor coil in summer, or a furnace that heats a few minutes then shuts off and blows cool air. Replace it and give the system time. If the coil has already iced up, switch the system to OFF and the fan to ON for a few hours to melt it, then restart in COOL with the new filter in. Ice does not clear in ten minutes.

Then walk the house. Supply registers hidden behind a sofa, under a long curtain or covered by an area rug are common after furniture gets rearranged. So are registers closed off in unused rooms, which people shut to save money and which mostly just raise duct pressure. Return grilles matter even more, and they are usually the big ones in a hallway or high on a wall. A return blocked by a bookcase starves the whole system.

Walk out to the outdoor unit and actually look at it. It needs clear air on all sides and above. The usual offenders here are a mulch bed that crept up over the base, grass clippings blown into the coil fins, cottonwood fluff in June, leaves packed against it in October, and a shrub grown until it touches the cabinet. Aim for two feet of clear space on every side and several feet of open air above the fan.

With the power off at the disconnect, you can clear leaves by hand and rinse the outside of the coil fins with a garden hose on low pressure, spraying from the inside outward where you can reach. Do not use a pressure washer, which bends the fins flat permanently. In winter a heat pump will frost and defrost normally, but a unit encased in solid ice, or buried by a plow bank or sliding roof snow, needs attention.

An air conditioner or a heat pump in cooling pulls a remarkable amount of water out of Mid-Atlantic summer air, and every drop has to drain. Look for a PVC pipe leaving the indoor unit and a drain pan under it. Standing water in the pan, water on the floor around the air handler, or a fresh ceiling stain under an attic unit all say the same thing: the drain line is clogged. In this climate the clog is almost always biological growth inside the pipe.

Most systems have a float switch, a small plastic device in the drain pan or spliced into the drain line. When water backs up, the float rises and opens the control circuit, shutting the system down deliberately so it does not flood your ceiling. A system that is simply dead in July with no other symptom is very often a clogged drain and a tripped float, not a broken air conditioner. Clearing the line resets it.