How to inspect a furnace control board?

Author: Dr. Hank Nolan PhD  |  Last update: Saturday, November 8, 2025

How to Check a Control Board
  1. Take off the furnace access panels. – Remove the front access panels. ...
  2. Check the control board. – Now you can see the control panel. ...
  3. Check the control board light. ...
  4. Test power going to the board. ...
  5. Check the terminals. ...
  6. Check the power going out from the control board.

How to test if a furnace control board is bad?

Turn the furnace off and check each control terminal of your control board. Start with either Hot or Ground then move on to Cooling, Heat, Fan, and Limit Switches. If your voltage meter readings show no power at any of these control terminals, then you should replace your control board.

What is the life expectancy of a furnace control board?

If the control board gets wet, it may fail. How long does a control board last on a furnace? The control board on a furnace should last about 15 to 20 years, which is the typical life span of a furnace. However, certain parts of the control board can fail early, or a power surge can damage the system.

How do you conduct a furnace inspection?

A Brief Furnace Inspection Primer
  1. Checking the Electrical Control Systems. ...
  2. The Gas Furnace Burner Must be Inspected and Cleaned. ...
  3. Examining the Heat Exchanger. ...
  4. Testing the Ignition System. ...
  5. Inspecting the Exhaust System. ...
  6. Checking the Gas Pressure. ...
  7. Testing the Gas or Oil Connections.

What makes a circuit board go bad in a furnace?

ESD or static electricity will cause a furnace control board to fail over time. Electronics fail over time, but other damage caused by a power outage, power surge, or another voltage spike like someone taking a power pole out. A blown fuse can prevent the circuit board from working too.

Furnace/AC How to Troubleshoot The Control Board

How do you diagnose a bad control board?

Now that you know where the control board is and what it does, let's explain the top signs that your control board is malfunctioning.
  1. Illuminated Warning Lights. ...
  2. Immobilized Switches on the HVAC Control Board. ...
  3. Faulty Soldering Connections. ...
  4. Interrupted Sequencing. ...
  5. Temperature Regulation Issues.

How much does a new circuit board for a furnace cost?

Depending on how technologically advanced your current furnace is, replacement costs for a new circuit board can run from around $300 to $1,200.

Who can inspect a furnace?

Category I and Category IV furnaces are inspected most often by home inspectors.

How much does a furnace inspection cost?

A furnace inspection costs an average of $80 to $100. Your cost may increase if more furnace repairs are needed, or based on the specifics of your HVAC system. If detrimental issues are uncovered, you'll be quoted for the repair or potential replacement of your HVAC equipment.

What does a thermocouple do on a furnace?

A thermocouple's primary responsibility is to monitor the performance of your furnace's pilot light. One end of the thermocouple is attached to the line that supplies gas to the pilot light. This allows the device to close off the gas supply to your pilot light at any time.

Is it easy to replace a furnace control board?

A furnace and AC board replacement is a rather tricky procedure that those with the necessary expertise should only carry out.

How does a control board go bad?

moisture in the system. high voltage. a loose wire connection that creates heat and burns through the wire. dirt in the terminals or relays in the control board.

Can you test a control board?

Connect the negative lead of a multimeter to the ground plane on the circuit board. Connect the positive lead of the multimeter to the power input of the board. Power on the board and check the voltage reading on the multimeter. The voltage reading should match the specified input voltage for the board.

How long does it take to replace furnace control board?

Replacing a furnace motherboard takes 20 to 30 minutes, depending on the furnace type, circuit board location, and accessibility. HVAC technicians may take up to 1 hour to run additional heating-system diagnostic tests.

What are the symptoms of a bad HVAC control module?

Since the module regulates the entire AC system, inconsistent cooling, out-of-date software, and uneven air distribution are typical signs of a broken AC control module.

What is the most expensive part to fix on a furnace?

A heat exchanger replacement is often one of the most costly repairs in a furnace, and the expense can sometimes rival that of installing a new furnace. Typical replacement costs vary widely but can easily reach several thousand dollars, especially if labor costs are factored in.

Can you clean your furnace yourself?

Your furnace may become dirty due to heavy use, requiring a cleaning mid-season, which you can likely do yourself – but if you're not comfortable, always call your technician for help.

Are HVAC inspections free?

The cost of an HVAC inspection is $300 on average, but can cost between $70 and $500 or more depending on the size of your home, type of HVAC system, and location of your HVAC unit in your home. The average HVAC inspection cost is $300, though homeowners can expect to pay anywhere between $70 and $500 per inspection.

Who do I call to check my furnace?

When you need help with your heating or air conditioning system, call a HVAC technician to inspect, diagnose, and perform any repairs. Let's dig into when and why you should hire a HVAC pro to restore your home to its usual temperature.

Does homeowners insurance cover furnace issues?

A standard policy typically won't cover the cost to replace your furnace if there was a mechanical problem, but you may be able to add an equipment breakdown endorsement for an additional cost that may provide coverage.

How long does a furnace inspection take?

How Long Does A Furnace Inspection Take? You can expect the inspection process to take up to an hour, depending on the configuration of your system. Upon completion, your service technician should present their inspection checklist and share any professional recommendations about your system.

How do I know if my furnace control board is bad?

If your control board is bad, you'll have trouble operating your furnace correctly. Control boards can fail for various reasons, but the tell-tale symptoms look the same: Warning lights flashing or staying on. Inability to settle on a stable temperature.

Is it worth replacing a control board on a furnace?

Conclusion. Replacing a furnace control board is an essential aspect of maintaining the efficiency and safety of your home's heating system.

How do you fix a bad circuit board?

How To Repair Circuit Boards
  1. Gather the tools and other materials that you'll need.
  2. Remove the damaged pad or component.
  3. Clean the track and remove solder.
  4. Place your copper tape over the track.
  5. Solder the joints.
  6. Restore the PCB through-hole.
  7. Place and solder your component.
  8. Trim excess tape from the repaired area.

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