What short cycling looks like
A healthy furnace in an Arvada winter runs ten to twenty minutes per cycle, three to six times an hour on a cold day, less on a mild one. A short-cycling furnace runs one to five minutes, shuts down, waits, and goes again. You will notice it as constant clicking and fan noise, uneven rooms, and a gas bill that does not match how cold the house feels.
It is worth fixing sooner than later. Every start is the hardest moment in a furnace's life: the ignitor glows, the inducer spins up, the blower motor draws its inrush current. A furnace that starts forty times a day wears parts out at four to five times the normal rate.
The causes, in order of how often they show up
Restricted airflow
The furnace makes heat faster than the blower can carry it away, the heat exchanger overheats, and the high-limit switch cuts the burners. The blower runs until things cool, the limit resets, the burners relight, and the loop repeats. Causes, in order: a clogged filter, closed or blocked supply registers, a return grille covered by furniture, a blower wheel caked with dust, or a filter that is too restrictive for the furnace (the pleated 1-inch "allergen" filters are a frequent offender on older Arvada furnaces with small return ducts).
Change the filter, open every register, and pull furniture off the returns. If the cycling stops, that was it.
Flame sensor
Burners light, run a few seconds, and drop out. Three tries and the furnace locks out for an hour. It looks like short cycling but the cycles are seconds long, not minutes. Cleaning or replacing the sensor is $150 to $300.
Limit switch
A limit switch that has weakened with age trips at a lower temperature than it should, so even a clean furnace with a fresh filter cycles off early. The tech reads the supply temperature and the switch rating and replaces it. $150 to $350 in Arvada.
Thermostat placement or a thermostat fault
A thermostat above a supply register, in direct sun, or on a wall shared with the furnace closet satisfies too quickly and shuts the furnace off before the rest of the house has warmed. Also common: a thermostat whose heat anticipator or cycle-rate setting is wrong for the furnace. Moving or reprogramming it is a small job.
Flue or intake restriction
On high-efficiency furnaces, snow drifting against the sidewall vent, ice in the exhaust elbow, or a nest in the intake makes the pressure switch open mid-cycle. After every storm, look at the PVC pipes on the outside of the house.
Oversized furnace
This one is common in Arvada for two reasons. Builders in the 1970s and 80s rounded up. And at 5,300 feet the derate rule (about four percent of output per 1,000 feet) was often ignored, so replacements got sized from a sea-level chart. An oversized furnace heats the space near the thermostat in minutes and shuts off, again and again, all winter. There is no repair for that; the fix is correct sizing on the next furnace, which is why the replacement quote here always includes a load calculation, not a nameplate match.
Carbon monoxide alarm going off? Get everyone outside and call 911. Then call us from the driveway. A cracked heat exchanger or blocked flue can put CO into the house with no smell at all, which is why every Arvada home with a gas furnace needs a working CO alarm on each floor.
What the fix costs this quarter
Prices verified September 2026| Cause | Cycle length | Parts and labor |
|---|---|---|
| Clogged filter or blocked registers | 2 to 5 minutes, warm then cold | $10 - $40 |
| Flame sensor | 3 to 10 seconds, then lockout | $150 - $300 |
| Limit switch | 2 to 5 minutes, filter is clean | $150 - $350 |
| Thermostat move or replace | Short cycles, rooms uneven | $100 - $350 |
| Blower wheel cleaning | Weak airflow, dust on the wheel | $150 - $400 |
| Pressure switch or vent clearing | Random shutdowns, worse after storms | $150 - $400 |
| Oversized furnace | Every cycle, every winter | Sized replacement, $3,500 - $10,400 |
| Compiled from published Denver-area contractor pricing and national cost guides, Q3 2026. Diagnostic $49 to $180, credited toward the repair. Written price before any work starts. | ||
A photo of the furnace sticker and the filter slot, sent through the photo quote, is enough for a tech to tell you whether this looks like a filter, a part, or a sizing problem before anyone comes out.