Furnace Not Working / No Heat In Arizona? A Troubleshooting Guide

Published by Air Conditioning Repair & Heating Repair Services Of Arizona — 24/7 emergency HVAC service statewide. Call (855) 424-2963.

Arizona winters are real above the Mogollon Rim. Flagstaff sees single digits, Show Low and Prescott freeze hard, and even Phoenix drops near freezing on January nights. A furnace that will not heat follows a predictable troubleshooting order. Start with the safe checks below, then call for heating repair if the problem is in the ignition, gas or safety circuit.

Step 1: Rule out the simple stuff

• Thermostat set to Heat, setpoint above room temperature, fresh batteries
• Furnace power switch (looks like a light switch near the unit) is ON
• Breaker for the air handler is not tripped
• Gas valve on the supply line is open and the propane tank is not empty
• The furnace door panel is fully seated — a loose panel opens a safety interlock
• Air filter is clean; a clogged filter causes overheat lockouts

Step 2: Read the status light

Most furnaces built after 1990 flash a diagnostic code through a small window, with the legend printed inside the door panel. Common patterns: pressure switch open (blocked flue or condensate), flame sensor failure (dirty sensor), limit switch open (overheating from restricted airflow), and ignition lockout after three failed tries. Power-cycling resets a lockout once — if it locks out again, the underlying fault is still there.

Step 3: Understand the common failures

Dirty flame sensor

The burner lights for 3–5 seconds, then shuts off, repeating three times before lockout. A carbon-coated sensor cannot prove flame. Cleaning is inexpensive and is the single most common no-heat repair.

Failed hot-surface ignitor

No glow, no light, no heat. Ignitors are brittle and fail on a predictable 4–7 year cycle.

Blocked flue or condensate drain

High-efficiency furnaces drain acidic condensate. A clogged trap or a bird nest in the flue opens the pressure switch and stops ignition. Check for water at the base of the unit.

Furnace short cycling

Heat for two minutes, off for two minutes, repeat. Causes include a restricted filter, closed supply registers, an oversized furnace, a failing limit switch, or a thermostat mounted in a draft. Short cycling wastes fuel and cracks heat exchangers — see furnace repair.

Cracked heat exchanger

The one repair no one should postpone. Symptoms include a yellow rolling burner flame, soot, a strong odor and CO alarms. If your technician red-tags the furnace, keep it off. Replacement options are covered under furnace installation.

Heat pumps and package units behave differently

Most Phoenix and Tucson homes heat with a heat pump or a rooftop package unit, not a gas furnace. A heat pump in heating mode delivers 90–100°F air — cooler than a furnace, and normal. Ice on the outdoor coil during a cold snap is only a problem if it does not clear during defrost cycles. See heat pump repair.

Call immediately if you notice

• A rotten-egg gas smell (leave the house first, then call the utility)
• A CO alarm sounding, headaches, nausea or drowsiness
• Soot, scorch marks or flames rolling out of the burner compartment
• Indoor temperatures below 50°F, or any risk of frozen pipes in the high country

We provide 24 hour heating repair and same-day furnace service statewide. Choose your city from the locations directory.