Regrettably, heat exchangers can’t be repaired; when a heat exchanger cracks, oxidizes, wears or rusts through it must be replaced. Since the heat exchanger is at the interior of the furnace, practically the whole furnace must be taken apart.
In many instances, a true crack will disturb the flame or set off a carbon monoxide detector in the home or work space. If you suspect a dishonest diagnosis, call us for a second opinion.
If a technician has doomed your furnace due to a cracked heat exchanger, I’d suggest clarifying to the technician that you’ll want to see the crack with your own eyes when they pull out the furnace. A trustworthy company should have no problem standing behind their conclusion. With the heat exchanger removed, the crack should be evident even to the untrained eye as in this picture.
More often than not, the cause of a cracked heat exchanger is lack of air flow or poor maintenance of the furnace. The primary cause of low airflow in a furnace is a dirty filter. Also, furnaces can be grossly oversized or used inaccurately which causes the heat exchanger to fail too soon. When a furnace is oversized, a number of problems can occur as well as short cycling and cycling on limit. Both of which cause the heat exchanger to heat up and cool down far more often than if the furnace was sized properly for the home or work space.