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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Furnace Repair in Saint Paul, MN
A Saint Paul furnace call, from Highland Park to Dayton's Bluff, is a $79 trip charge up front, waived when you say yes to the repair. In old bungalows and duplexes we test draft and sort out which unit is actually down before replacing parts.
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 November 10, 2026
What do common furnace repairs cost in Saint Paul?
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.
Symptom guides: Blinking light codes · Pressure switch trips · Strange noises · Leaking water · Signs your furnace needs a technician
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
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Furnace repair near Saint Paul
- West St. Paul, MN furnace repair · 3 mi
- Maplewood, MN furnace repair · 5 mi
- Roseville, MN furnace repair · 5 mi
- Falcon Heights, MN furnace repair · 5 mi
- South St. Paul, MN furnace repair · 5 mi
- Little Canada, MN furnace repair · 5 mi
Brands we repair
Guides on furnace repair
Frozen Condensate Line on a High-Efficiency Furnace
Furnace quit in a cold snap because the drain line froze? How to thaw it safely, stop it refreezing, and our $79 trip charge, waived with the repair.
Read the guideLennox Furnaces Compared: Merit, Elite and Signature
Lennox Merit, Elite and Signature furnaces overlap more than the names suggest. Learn to decode a model number; our 96–98% AFUE installs run $6,500–$9,500.
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Heat out? AC quit? Call or send a request.