The short answer
Fix it if the furnace is under about 15 years old and the repair is a common part. Start comparing replacement if it is past 15, the repair is a major component, or this is the second or third call in two winters.
Repairs that are almost always worth it
These parts fail on furnaces of every age, cost little relative to the furnace, and we carry most of them on the van.
- Flame sensor cleaning or replacement
- Hot surface igniter
- Run capacitor or blower relay
- Pressure switch or a blocked condensate line on a high-efficiency furnace
- Thermostat or low-voltage wiring faults
Repairs that should make you pause
These are the expensive parts. On a younger furnace they are still worth fixing, especially under warranty. On an older one, price the replacement next to the repair before you decide.
- Inducer motor or blower motor on a furnace past 15 years
- Main control board on a discontinued model
- Gas valve
- Any second major repair within two heating seasons
When we will tell you to replace it
A cracked heat exchanger can let combustion gases into the airflow. We show you the crack on camera or with the combustion readings, shut the furnace down, and quote both a replacement and, if the furnace is still under parts warranty, the exchanger swap. We will not leave a furnace running with a confirmed crack.
The rule of thumb we use
Multiply the furnace’s age by the repair price. When that number gets close to the cost of a new furnace, replacement is usually the better money. It is a starting point, not a verdict. A well-maintained 18-year-old furnace in a house you are selling next spring is a different decision from the same furnace in a house you plan to stay in.
What changes the answer
- Efficiency. Going from an older 80% AFUE furnace to a 95% unit cuts the gas used for the same heat.
- Comfort complaints. If rooms were already uneven, replacement is the moment to fix sizing and ductwork.
- Heat pump plans. If you are considering a heat pump, a furnace near the end of its life is a good reason to price both together.
- Rebates and financing. These can narrow the gap between repair and replace.