Cracked Heat Exchanger: Symptoms, How It's Confirmed and What to Ask For
Signs of a cracked furnace heat exchanger, how a technician confirms one, what to ask for if your furnace is red-tagged, and when to repair or replace it.
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Furnace Repair in Saint Paul, MN
We repair furnaces across Saint Paul, from Highland Park to Dayton's Bluff, 7am–9pm, seven days a week. The visit is a $79 trip charge, waived when you approve the repair, and the flat-rate price is in writing before we start. Many furnaces here replaced gravity heat decades ago and still use those original ducts.
Furnace repair calls in Saint Paul homes
Most Saint Paul furnaces sit in basements built for something else. The 1910s and 1920s foursquares and bungalows in Macalester-Groveland, Hamline-Midway and Como started on gravity heat, and the forced-air furnace that replaced it often pushes air through the original oversized ducts and a couple of big floor returns. Low ceilings put the flue pipe tight to the joists, and many 80% furnaces still vent into a brick chimney shared with the water heater, so we test draft and look at the chimney base along with the failed part.
Duplexes add another layer: two furnaces side by side, two thermostats, and ducts for the upper flat that wander through the lower one. The first job on a January night is sorting out which unit is actually down. Xcel Energy is the gas utility citywide, so a gas smell is a call to Xcel from outside the house before it is a call to us.
Updated September 23, 2026
How much does furnace repair cost in Saint Paul?
Every furnace repair call in Saint Paul starts with a $79 trip charge, waived when you approve the repair, and a written price before any work. Same prices in Saint Paul as in every town we serve. National averages (HomeGuide, 2026), not our prices: a limit switch $100–$375, a control board $300–$650, an inducer motor $400–$1,100. More in the furnace repair cost guide. For what drives a quote locally, see HVAC cost in Saint Paul.
Signs your furnace needs a technician
- The inducer starts, the igniter glows, then the burners never light
- The burners light for a few seconds and shut off, over and over
- The furnace runs but the vents blow cool air
- A blinking code on the control board, or the furnace has locked out
- Your CO alarm went off or the burner flames look lazy and yellow
- New banging, squealing or grinding when the furnace starts
- Water pooling around a high-efficiency furnace
More detail on our furnace repair page.
Symptom guides: Blowing cold air · Won't ignite · Short cycling · Blinking light codes · Pressure switch trips · Strange noises · Leaking water · Burning smell · Red tag · Carbon monoxide
Furnace repair in Saint Paul: questions
The furnace in our converted-gravity Saint Paul house keeps shutting off and restarting. What causes that?
Usually the high limit. When air can't move across the heat exchanger fast enough, it overheats and the limit switch shuts the burners off until it cools. In these houses the culprit is often the return side: a packed filter, a floor return covered by furniture, or an old cold-air return that got closed in when the basement was finished. A weak blower motor can do it too. We measure temperature rise and static pressure to find which.
Our CO alarm went off near the furnace in our older Saint Paul house. What should we do?
Get everyone outside, then call the fire department or Xcel Energy from there. In houses this age, a common cause is a blocked or deteriorating brick chimney: fallen tile or mortar at the base chokes the flue, and exhaust from the furnace or water heater spills back in. A cracked heat exchanger is another. Minnesota law requires working CO alarms within 10 feet of every sleeping room, so after the repair, check those too.
More in Saint Paul
- Furnace replacement in Saint Paul
- AC repair in Saint Paul
- AC replacement in Saint Paul
- Heat pumps in Saint Paul
- Mini-splits in Saint Paul
- Boiler service in Saint Paul
- Tune-ups in Saint Paul
- HVAC cost in Saint Paul
- All HVAC service in Saint Paul
Furnace repair near Saint Paul
- West St. Paul, MN 3 mi
- Maplewood, MN 5 mi
- Roseville, MN 5 mi
- Falcon Heights, MN 5 mi
- South St. Paul, MN 5 mi
- Little Canada, MN 5 mi
Brands we repair
Guides on furnace repair
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Read the guideFurnace Blowing Cold Air: What to Check, in Order
Cold air from the vents with the heat on? The order a technician checks: fan setting, burners, limit trips, flame sensor, vents, gas supply and ductwork.
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Furnace repair in Saint Paul? Call or send a request.