Furnace won't ignite / no heat
Ranked from 3,800 repairs on furnaces with this symptom. Narrow it below and the ranking recomputes — the more you can tell us about what your furnace is actually doing, the shorter this list gets.
Before you start — Kill the power before you touch anything gas · electrical safety
Switch the furnace off at the service switch AND at the breaker — they are not the same thing, and the blower can start on its own while your hands are in the cabinet. The parts ranked below are safe DIY swaps with the power off. Gas valve and heat-exchanger work is licensed-tech territory in most jurisdictions.
If you smell gas: stop. Don't switch anything on or off, don't use your phone indoors. Leave the building and call your gas utility from outside.
Narrow it down
My furnace is blinking an error code — what does it mean?
Count the flashes and read them against your unit's code chart before buying anything — the code is the furnace telling you exactly what it sees, and it beats any ranking we can offer. Across these repairs the control board accounts for 41%, a pressure switch open or intermittent for 27%, and a failed flame sensor for 18%.
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Also check — 41%
CTB-1084
Integrated Furnace Control Board
23 in stock · ships today
$128.00 Pro price $108.80 save $19.20 (15%)41% of matching repairsLockout and internal-fault codes point at the board itself — but read the code chart first: most codes name a sensor, not the board.
Try this first: Free and faster than any of this: match your flash code against the error code chart for your unit.
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Also check — 27%27% of matching repairs
Pressure switch codes are the most common flash code on an 80% furnace, and the most commonly misread — a blocked flue throws the same code as a dead switch.
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Also check — 18%18% of matching repairs
Flame-sense lockout codes usually clear after cleaning the rod.
Try this first: Clean the rod first — 5 minutes, free.
The remaining 14% of matching repairs resolved without a replacement part — a filter, a reset or a thermostat setting.
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