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Furnace Blowing Cold Air: Repair or Replace? A North Las Vegas No-Heat Call

When a furnace blows cold air, the blower is running but the burners aren’t lighting or aren’t staying lit. A dirty flame sensor, a failed igniter, a tripped safety switch, a gas valve problem, or a thermostat fan set to “On” are the usual causes, and many are single-part repairs. Whether to repair or replace comes down to the furnace’s age, its condition, and whether the AC is due soon too. On December 2, 2025, a North Las Vegas home in the 89084 ZIP had no heat and cold air from the vents, starting the day before. After our diagnostic, the homeowner chose a full new heating and cooling system.

What We Found

The homeowner called with no heat since the previous day and cold air blowing from the vents. When we photographed the thermostat, it was switched off with the house at 66 degrees. The furnace is a Bryant in the attic. We opened it up and checked the control board, the gas valve, and the blower motor, which had a heavy coat of dust, and looked over the outdoor AC unit.

How We Fixed It

Reviewed the findings with the homeowner after testing.
The homeowner chose to replace the full system with a RunTru by Trane 5-ton straight cool system rated 14.3 SEER2, paired with an 80% efficient gas furnace.
“Straight cool” means the outdoor unit handles cooling only, and the gas furnace handles all of the heat.

How it turned out

The homeowner approved the full system replacement, which covers both the heating and the cooling side of the house.

Why is my furnace blowing cold air?

Start with the easy checks. Make sure the thermostat is set to Heat and the fan is on Auto, since “On” runs the blower even when the burners are off. Then check the filter. If those are fine, the furnace is likely shutting off its burners for a reason: a dirty flame sensor, a weak hot surface igniter, an open safety switch, or a gas valve that won’t open. Many furnaces flash a code on the control board that points to the cause.

Should I repair or replace a furnace that blows cold air?

Repair makes sense when one part failed and the furnace is otherwise in good shape. Replacement starts to make sense when the furnace is older, repairs keep adding up, or the AC is the same age and close to the end of its life. In Las Vegas, the AC usually wears out first, so many homeowners replace both together. Our page on full system replacement walks through that decision.

What does an 80% furnace mean?

It’s the furnace’s efficiency rating (AFUE). About 80% of the gas it burns becomes heat in your home, and the rest leaves through the vent. Las Vegas winters are short and mild, so 80% furnaces are a common, practical match here.

Safety note: HVAC repairs involve high voltage, refrigerant and, on gas furnaces, combustion gases. Leave them to a licensed technician.

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