HVAC troubleshooting guides

Heating

• Furnace won't ignite? Nine checks, in the order a tech runs them — thermostat, power, filter, gas, ignitor, flame sensor, condensate, error codes.
• Furnace blowing cold air? Seven causes, in order — fan settings, high-limit trips, ignition, disconnected ducts, and true undersizing.
• Furnace making loud noises? What each sound means — the startup boom that means shut it down, plus squeals, rattles, hums, and clicks.
• Thermostat blank or not working? Seven checks — batteries, furnace power, the $3 board fuse, the float switch, and smart-thermostat C-wire traps.
• Furnace short cycling: why it turns on and off every few minutes — high-limit trips, thermostat placement, oversizing, and when it's a part failing.

Cooling

• AC blowing warm air? Eight checks, in order — fan settings, frozen coils, cottonwood-clogged condensers, capacitor symptoms, and the truth about refrigerant.
• AC leaking water? First-hour steps, then the causes — clogged drains, frozen coils thawing, rusted pans, and dead condensate pumps.
• AC won't turn on at all? Seven checks before you call — blank thermostats, the outdoor disconnect, the condensate float switch, and surge casualties.

Before any replacement conversation

Troubleshooting ends in a replacement quote more often than it should. If a tech tells you the system is done, sanity-check the numbers against the Denver-metro HVAC cost guide — installed price ranges for furnaces, ACs, and full systems, plus the repair table these guides draw from.