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 igniter glows but the burners never light — what's wrong?
If the igniter glows and gas never lights, the gas is not arriving: about 52% of these repairs come back to the gas valve failing to open. Check that the gas is actually on and that the valve is getting 24V before condemning it — and note that gas valve replacement is licensed work in most jurisdictions. A pressure switch stuck open (26%) or a board that never energises the valve (15%) produce the same symptom.
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Most likely — 52% Licensed tech install
GSV-36J
36J Series Gas Valve, 24V
Low stock — 12 left · ships today
$96.50 Pro price $82.03 save $14.47 (15%)52% of matching repairsIgniter hot, no flame, means gas never arrived. Confirm the manual shutoff is open and that the valve sees 24V during the trial-for-ignition window — if it is powered and still doesn't open, the valve has failed.
Try this first: Free first: check the manual gas shutoff and, if you have other gas appliances, confirm they still light.
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Also check — 26%26% of matching repairs
Some boards run the igniter but hold the valve closed while the pressure switch is open — you get the glow and nothing else.
Try this first: Check the switch hose for water or cracks first; that is free.
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Also check — 15%
CTB-1084
Integrated Furnace Control Board
23 in stock · ships today
$128.00 Pro price $108.80 save $19.20 (15%)15% of matching repairsA board that heats the igniter but never energises the valve output is failing mid-sequence. Meter the valve terminals during trial-for-ignition to separate this from a dead valve.
The remaining 7% of matching repairs resolved without a replacement part — a filter, a reset or a thermostat setting.
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