Cracked Heat Exchanger: Symptoms and How It's Confirmed
Signs of a cracked furnace heat exchanger, how a technician confirms it with a camera and CO readings, what to do after a red tag, and repair vs replace.
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For a Maplewood furnace repair, approve the fix and we waive the $79 trip charge, and the flat-rate price is written before work starts. North-end ramblers often vent the furnace and water heater up one old chimney, so we check its draft.
In Maplewood's north-end ramblers from the 1950s and 1960s, the furnace and gas water heater usually share one masonry chimney, and plenty of repair calls begin there. A chimney partly blocked by a crumbling clay liner or a bird's nest drafts weakly; the furnace's rollout or pressure switch trips and the furnace locks out. We check the draft and the flue along with the furnace, because relighting a furnace into a bad chimney only brings the problem back.
Split-entries farther south and east put the furnace in a lower-level utility room, often finished around it, where the filter and condensate trap are easy to forget. Townhomes add closets with tight clearances. The parts that fail are the usual ones: igniters, flame sensors, inducers, blower capacitors. Xcel Energy is the gas utility in Maplewood, so if you smell gas, leave the house and call Xcel's gas emergency line first. We handle the furnace once it's safe.
Updated October 27, 2026
National averages (HomeGuide, 2026), not our prices: an inducer motor $400–$1,100, a PSC blower motor $500–$1,400, a variable-speed (ECM) blower motor $800–$2,300. More in the furnace repair cost guide.
Symptom guides: Carbon monoxide · Blowing cold air · Won't ignite · Short cycling · Signs your furnace needs a technician
No. That's usually a spill or blocked-vent switch, and it trips when exhaust backs into the house instead of rising up the chimney. Pressing it again sends more exhaust into your basement. Turn the furnace off and call us; if a CO alarm sounds, get everyone outside and call 911 from there. We'll check the chimney draft, the flue connector and the furnace, and give you a written price for what's wrong.
Finished rooms can choke a furnace. A solid door, a room packed with storage, or drywall that closed off the old air supply can starve the burners of combustion air, and a return grille blocked by furniture raises the temperature across the heat exchanger. Either one can trip a safety switch and lock the furnace out. We check the room's air supply along with the furnace; a louvered door or a combustion-air duct often fixes it.
Signs of a cracked furnace heat exchanger, how a technician confirms it with a camera and CO readings, what to do after a red tag, and repair vs replace.
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