Gas Furnace Won’t Ignite?

Most Tampa Bay homes run on heat pumps, but there are real pockets of gas furnaces out there, mostly in older Seminole Heights, Hyde Park, and South Tampa houses, plus a fair number of snowbird-built homes from the 80s and 90s. When that gas furnace fires maybe 30 nights a year (the ones below 50 degrees), the failures stay hidden until the first real cold snap, and that is when our phones start ringing nonstop.

Here is the ranked list of what we actually find when we pull a panel on a Tampa gas furnace that won’t light:

1. Hot surface igniter (HSI) cracked or failed. This is the single most common cause, hands down. A hot surface igniter is a thin silicon nitride or silicon carbide element that glows orange to ignite the gas. Lifespan is typically 5 to 7 years, and Tampa furnaces that sit unused for 9 months a year are not exempt. Thermal cycling and humidity inside the cabinet kill them.

2. Flame sensor dirty. The flame sensor is a thin metal rod that sits in the burner flame and confirms ignition happened. Over time, a layer of oxidation builds up and the sensor stops detecting the flame, so the gas valve shuts off after 5 to 10 seconds and the furnace locks out. A wipe with fine steel wool fixes this in minutes.

3. Bad thermocouple. Older Tampa furnaces with a standing pilot light use a thermocouple instead of a flame sensor. If the pilot lights but won’t stay lit, the thermocouple is usually the culprit.

4. Gas valve failure. No fuel reaches the burners even though the igniter glows. Less common, but happens.

5. Pressure switch failure. The inducer motor pulls a vacuum on the pressure switch to confirm the vent is clear. A bad switch (or a blocked vent from a wasp nest, common down here) keeps the sequence from advancing past the inducer stage.

6. Control board failure. The brain of the furnace fails, often from heat or moisture damage. You will sometimes see a blinking error code through the sight glass.

7. Gas supply issue. Peoples Gas service interruption is rare but possible, also check that the gas valve at the unit and the meter are both open.

Real Tampa pricing, no surprise fees, FREE estimates on every visit:

• Hot surface igniter replacement: $245 to $445. 30 to 45 minutes. We carry universal HSIs for almost every brand.
• Flame sensor cleaning or replacement: $145 to $195. 15 to 25 minutes. Most often a clean fixes it; replacement runs slightly higher.
• Thermocouple replacement: $195 to $295. Older standing-pilot furnaces only. Includes pilot adjustment.
• Gas valve replacement: $445 to $795. Brand and configuration drive the spread.
• Pressure switch replacement: $245 to $395. Includes vent inspection to make sure the new switch isn’t fighting a real airflow problem.
• Control board replacement: $445 to $795. Universal boards on the low end, brand-specific OEM boards on the high end.
• Filter replacement: $0 to $50 DIY. Standard 1-inch filters at any hardware store.
• Annual furnace tune-up: $145 to $295. The right move every fall before the first cold front. We clean the burners, check the HSI, wipe the flame sensor, test gas pressure, and run the safety circuit.
• Full gas furnace replacement: $4,995 to $8,995. Rare in Tampa, since most homes don’t justify a new gas system.
• Heat pump conversion if the gas furnace is past its life: $7,500 to $11,500. Federal 25C tax credit applies (up to $2,000 back). Cheaper to operate year-round in our climate, and you get real cooling out of it instead of just heat.

FREE estimates on any replacement or major repair. Call (813) 343-2212 for same-day service.