No Heat? Safe Checks Before You Call

What should you check first when there is no heat?

Check the thermostat first: it should be set to Heat, set a few degrees above the room temperature, and showing a lit display. If the screen is blank, replace its batteries if it uses them.

Next, confirm that power reaches the furnace. Look for a tripped breaker in the panel and reset it once; if it trips again, leave it off and call a technician. Then find the furnace's service switch, often on or near the furnace, and make sure it is on. Carrier's installation manual warns that "there may be more than one disconnect switch", so check every one.

If the thermostat is the problem and its manual allows an owner swap (never a 120- or 240-volt baseboard thermostat, which is electrician work; turn the breaker off first, and if unsure call a qualified technician), PlumbingSupplyAndMore's thermostats (part of Upvalley Heat's ownership group) show the kinds sold; a heat pump or multi-stage system is safer left to a technician. Black Hills Energy's 2026 rebate form lists up to $100 for a smart thermostat, with applications due January 31, 2027 (see utility rebates).

Numbers on the checklist

• 12 inMinimum vent clearance over predicted snow depthCarrier, Lennox and Trane manuals
• $200–$1,000Usual LEAP heating benefit per seasonColorado CDHS
• 300 ftDistance to walk before calling about a gas smellBlack Hills Energy

Which no heat checks are safe for a homeowner?

The safe no-heat checks are the ones that need no tools and open nothing: the thermostat, the breaker and service switch, the air filter, the furnace door, the registers, and snow around the outside vents and any outdoor heat pump unit. Carrier draws the line plainly: untrained people "can perform basic maintenance functions such as cleaning and replacing air filters."

A clogged filter can starve the furnace of air. Carrier says to check the filter each month, never to run the furnace without one, and to point any airflow arrow toward the blower. Lennox says a filter must be in place whenever the unit runs. For filter types and sizes, see wildfire smoke filtration.

The furnace's front panel matters too. Carrier's blower door switch "opens 115-v power to control", so a panel left loose after a filter change can stop everything. Seat the panel firmly; never tape or hold the switch closed.

How do snow-blocked vents shut a furnace down?

A high-efficiency furnace pulls combustion air in through one plastic pipe and pushes exhaust out through another, and if snow packs either one, the furnace's safety controls stop it. That is why Carrier, Lennox and Trane call for vent ends to sit 12 inches or more over the deepest snow anticipated.

After a storm, walk outside and check both pipes. The National Weather Service says to make sure a gas furnace vent is not blocked by a drift as soon as it is safe to go out, and Black Hills Energy says to keep exhaust and air intake areas clear. Clear packed snow by hand or with a soft brush; no shovels or tools that could crack the plastic.

If ice keeps building on the exhaust, or the furnace keeps locking out, call a technician; the vent may need to be raised or rerouted. A frozen or backed-up condensate drain can shut a furnace down too, and protecting it is installer work (see frozen pipes). A heat pump's outdoor unit needs the same care: Lennox says to raise it above the average snow line.

What should you never touch?

Never open or adjust gas valves beyond the on and off steps in the owner's manual, and never touch burners, igniters, orifices, pressure switches or altitude settings. Lennox's EL297 manual tells owners "Use only your hand to move switch. Never use tools," and not to force a control that will not move; it also says not to light the burners by hand and not to use a furnace if any part has been underwater.

Never bypass or jumper a limit, rollout, pressure or flame switch. These switches exist because, as Trane's high-altitude kit sheet puts it, a furnace set up wrong can produce carbon monoxide. Leave refrigerant to the professionals too: the EPA requires Section 608 certification for technicians who service equipment that could release refrigerant.

Many modern furnaces light with a hot-surface igniter (Lennox's EL297 uses one), and a worn igniter is a part a technician diagnoses and replaces, matched to the furnace model. If you are unsure, stop and call a qualified technician.

Carbon monoxide alarms belong on every level of the home (CPSC advice); Colorado's 2009 law requires one no farther than 15 feet from each bedroom entrance when a home is sold or a fuel-fired appliance is replaced under permit, among other cases. If an alarm sounds or anyone feels sick, get everyone outside, then call 911. More is on the carbon monoxide page.

When is it time to call a heating technician?

Call a heating technician when the five safe checks are done and the house is still cold, or straight away if a breaker trips twice, the exhaust keeps icing, water pools around the furnace, or the furnace starts and shuts off again. The CDC and EPA both advise a yearly check of gas heating equipment by a trained professional.

Call 911 and the gas utility instead if you smell gas: leave first, do not switch lights on or off or use phones inside, then call from about 300 feet away, as Black Hills Energy advises. Do not try to fix gas lines or equipment.

Help with the bill exists. Colorado's LEAP program takes heating-assistance applications from November 1, 2026, to April 30, 2027, usually paying $200 to $1,000 a season, and links to programs that help repair or replace a heating system.

How do you choose a heating technician?

Choose a licensed contractor who pulls the permit, knows your furnace's high-altitude requirements and holds EPA Section 608 certification if refrigerant is involved. Aspen and Glenwood Springs say replacing a furnace or boiler needs a mechanical permit; Pitkin County, Basalt and Carbondale publish mechanical permit applications, so expect one and ask your building department. Pitkin County also requires mechanical contractors to hold a City of Aspen contractor license.

Ask how the contractor sets up a furnace for your elevation: every town in the valley sits above the point where most makers call for high-altitude parts or settings, and the furnace altitude derating page explains why the model's manual decides. Ask for a written scope that covers venting, the condensate drain and freeze protection.

For a sense of what a full-service shop covers, Central Plumbing & HVAC's heating services page (part of Upvalley Heat's ownership group) lists the heating work such a company handles. That company is in Pennsylvania and does not serve Colorado; in the valley, look for a local licensed contractor offering the same range.

Lift-line questions

Other cold-weather pages

• Folder: The cold snaps overview
• Cold snaps: Thawing and protecting pipes
• Cold snaps: Heat and safety when the power fails
• Heat pumps: Backup heat and dual fuel