How To Check Control Board On Furnace? Vital Tips And Guide

Control Board in Furnace

A furnace’s control board is key. It controls the heating system’s functions, from the fan motor to the gas valve. Malfunctioning boards can cause blower issues or shorts in other parts.

Find the board and turn off the breaker. Use your user manual or access panel to find the diagnostic light and check it. Look for solder joint burn marks that could signal problems.

Before making any repairs, make sure there is no voltage going to the system. Disassemble the system and test each wire. Mark where they were connected.

If tests and visual inspections check out, you may need a new board. Contact HVAC technicians to install or fix it. Proper HVAC work protects you and your family from costly damages and keeps them warm in winter! The diagnostic light is like a mood ring for your HVAC system.

How To Check Control Board On Furnace

The Diagnostic Light

When it comes to furnace control boards, look out for the diagnostic LED light. It is an important element in identifying and solving HVAC system problems. Depending on the board, the LED can be in different places. It will blink and form a pattern that can help you detect the issue. Each manufacturer has its way of using this tool.

It’s possible that your furnace control board doesn’t have a diagnostic LED. In that case, check the user manual or wiring diagram. Make sure the power is off first. Then, test the components with a multimeter.

Recently, I had to replace an old control board. Before calling an HVAC technician, I followed the user manual steps. When nothing worked, I got a new integrated furnace control board and installed it.

Knowledge of the diagnostic LED light is really beneficial. It can save time and money when maintaining or troubleshooting. Get familiar with the furnace circuit board – it’s just wiring.

Checking the Circuit Board

Why did the furnace feel left out? Because everyone was talking about the control board. Checking a furnace control board is something most homeowners are hesitant to do. It can be risky and complex. But with the right steps, it’s possible to diagnose and fix the issue. Here’s how:

  1. Safety first! Turn off the electricity to your unit so you don’t get shocked.
  2. Access: Find the access panels and remove them with screws or clips. Locate the control board by following wiring diagrams, and service manuals, or asking an HVAC technician.
  3. Diagnosis: Look for blown fuses or melted wires on the board. Check all wire connections for damage or looseness and re-solder/replace if needed.
  4. LED Light Indicators: Look for any marks on the PCB that indicate an error code (labeled in your service manual).
  5. Testing Voltages: Use a multimeter to test the high and low voltage wires at terminals marked H, C, W, G, R, or V. They should show correct voltages (<24VDC – low voltage circuits/HI/120VAC – Line Voltage circuit).
  6. Re-test and Endorsement: After repair/replacement of any component, test all associated components. This includes the door switch/fan relay/vacuum pressure/safety switches/draft inducer motor/gas valve sequence from the control panel.


  • When testing with a meter, make sure probes are connected properly.
  • Vacuum tubing should be checked for blockage.
  • Do a quick smell check to identify burnt solder joints.
  • Be careful when disconnecting Molex plugs, they can be brittle.

Checking the Door Switch

When it comes to the door switch on your furnace control board, it’s important to be careful. Here’s a simple 4-step guide:

  1. Turn off the power supply. For safety, switch off the HVAC system from the main circuit breaker.
  2. Find the door switch. It’s usually near an access panel. Look for a button or lever attached to a metal bar on the inside of the door.
  3. Test continuity. Use a multimeter and place one lead on each terminal. Check the needle movement when you press and release the button or lever.
  4. Replace or repair. If there’s no continuity, the switch may need replacement or repair. Get advice from an expert HVAC technician.

Keep in mind, the issue may not be just the door switch. If you’re confused, don’t hesitate to ask a pro.

Fun fact – Repair Clinic says that burnt solder joints and faulty connection points due to heat buildup can cause furnace control board failure. Transformers and wiring diagrams are helpful for this complex task.

Checking the Transformer and Wiring Diagram

To check a transformer and wiring diagram, it’s important to take specific steps. The transformer changes high voltage to low voltage so appliances can use electricity safely. Looking at the wiring diagram will show how the system is connected and check for problems.

These steps are needed to check the transformer and wiring diagram:

  1. Shut off power
  2. Locate the transformer and test voltage with a multimeter
  3. Check wiring connections according to the diagram
  4. Look for loose or damaged wires
  5. Test components individually with a multimeter

It’s essential to note that transformers generate heat, so be cautious when assessing them. Also, always check voltage carefully before touching or repairing parts of the HVAC system.

If you smell burning from the furnace or hear strange noises coming from your HVAC unit, there might be a problem with the control board or another component in your heating system.

Overall, checking the transformer and wiring diagram is a step in maintaining your furnace. If you’re concerned about furnace performance or have noticed issues during regular use, consult a professional HVAC technician.

Don’t wait until it’s too late; call a professional now to assess your heating system and prevent expensive repairs later!

Checking for Voltage

When inspecting your furnace’s control board for voltage, there are some things to remember. Here’s the scoop:

  • Start by cutting power to the HVAC system and opening the furnace access panels.
  • Use a multimeter to test for line voltage. Set the meter to 120VAC and touch one lead to the white “common” wire and the other to the wire that activates relays or the fan motor.
  • To test for low voltage, set the meter to 24VAC. Touch one lead to the R terminal on the circuit board, and the other to either of the remaining terminals (W, Y, G).
  • If you get 24 volts, things are working. But if you don’t, there could be an issue with a component.
  • You may also use a junction box or Molex plug tester to check for continuity across certain points in the circuit board. This can uncover wiring issues or short circuits.

It’s tricky to diagnose with these tests alone – so it’s wise to call a pro if unsure. When examining the circuit diagram, check all solder joints and connection points. If burnt smells or scorch marks are present, you need a new board. Also, make sure terminal strips are free from tape residue, corrosion, and moisture. I always keep my pressure and vacuum switches in check – don’t want my furnace to feel the cold!

Checking the Pressure Switch and Vacuum Switch

HVAC system troubleshooting starts with checking the pressure switch and vacuum switch. They work together to make sure your furnace is safe. Here are 3 easy steps:

  1. Locate the switches. They’re often near the blower motor or on the front of the control board.
  2. Check continuity with a multimeter. If there’s no continuity, one of the switches could be the problem.
  3. Test the pressure switch output voltage using a volt meter. Use caution when running tests or replacements.

A customer called us with a gas furnace issue. The pressure switch was malfunctioning. We replaced the control board and the furnace worked!

Checking these smaller components can be tricky. As pros, it’s our job to spot any safety hazards. When it comes to the gas valve and ignitor, don’t play with fire!

Checking the Gas Valve and Ignitor

It’s important to take a professional approach when checking your furnace’s gas valve and ignitor. Here’s a 3-step guide:

  1. Turn off the electricity. Ensure your HVAC system is completely off at the unit or circuit breaker. This prevents any electrical problems.
  2. Look for damage. Check for burn marks, leaks, or disconnections that could affect your system.
  3. Test functionality. Use a multimeter or voltage meter to measure the voltage output on the gas valve and ignitor. If you’re not confident in doing this, call an expert.

Issues with the gas valve or ignitor can be serious. It’s key to conduct regular checks. But if you suspect a problem, don’t hesitate to get help from a pro. Don’t wait too long – keep your family safe and warm by maintaining your furnace! Plus, don’t forget to inspect the blower motor and fan – maybe add some tape – to prevent it from malfunctioning.

Checking the Blower Motor and Fan

To guarantee your furnace is running smoothly, it’s essential to check the blower motor and fan. They work together to distribute hot air throughout your house. Follow these 3 easy steps to inspect them:

  1. Set your thermostat to ‘fan’ and turn up the heat. Open the furnace access panel, locate the blower motor, and inspect its wire connections. If you find any loose wires or burnt marks, use a voltmeter to test the voltage wires.
  2. If all looks good, switch off the power supply and unplug the Molex plug from the circuit board. Take a reading with your multimeter by placing one lead on terminal ‘C’ and another on terminal ‘HI’, then set your meter to read Volts AC. If you get around 120VAC hot when testing, there’s no problem with your fan motor.
  3. If everything is okay, turn the unit back on and observe how it works overall. If you smell something strange or it overheats, there could be another underlying problem in addition to checking the blower motor and fan.

Remember to make sure all connections are soldered securely, and that the wire connections aren’t damaged. By following these steps, you’ll spot issues that others may miss. Don’t risk burning out and damaging other furnace components – get them checked right away! In the winter months when temperatures drop below freezing, the last thing anyone wants is for their heating system to break down suddenly. So call a professional HVAC technician who can run tests before replacing parts like gas valves if needed. Ready to boost your DIY skills? Here’s how to replace your furnace control board like a pro.

Replacing the Control Board

Furnace repair can be tricky, but DIY-ing it can save you money on service calls. Here’s a 4-step guide to replacing your furnace’s control board:

  1. Turn off the power – Flip the circuit breaker that supplies the furnace.
  2. Remove Old Board – Unscrew any mounting screws and take out the old board. Note the wire connections.
  3. Install New Board – Place the new board in its spot. Connect all wires according to the wiring diagram.
  4. Turn On Power & Test – Reattach any mounting screws, turn on the switches in the circuit breaker box, and test your heating system.

Pro tip: Have all your materials ready before starting. This’ll help prevent damage to solder joints or connections.

And remember: when disconnecting terminals, use needle-nose pliers – never pull the wire!

Testing the Furnace Components

Before testing furnace components, it’s best to check all the power sources. Use a multimeter to test voltage wires for high and low voltage. Inspect wire connections and solder joints. Assess the switches with a multimeter. Check the ignition sequence of the components like the ignitor, gas valve, and relay. Use an ammeter clamp meter to check voltage leads supplying fans. Additionally, create a checklist using marks or signs for each component. Clean away dust from connectors before every test. Following these steps will help identify the issue quickly and avoid unexpected casualties. In any case, if the issue is too complex, consider calling for professional HVAC service.

When to Call for Professional HVAC Service

As an HVAC technician, I understand that there are times when a professional service call is needed. It may be time to call in the experts if your furnace needs more than a simple filter replacement and thermostat check.

For example, if the furnace control board has problems, it can be difficult for someone inexperienced to diagnose and fix them. Plus, if you detect strange smells or sounds from your HVAC system, professional help is always best.

Sometimes, even if everything looks okay and there are no signs of failure, there could still be something wrong. A professional repair service has the means and tools to test all the connection points of HVAC systems to avoid any future problems.

I once went to a service job where a homeowner had tried to replace their own furnace circuit board without disconnecting the power source. This caused a short circuit which damaged the new board and other components. It was much more expensive to repair than if the homeowner had called for professional help.

If you’re not sure whether to get HVAC assistance, it’s better to be safe than sorry. Contact us and we’ll check it out, saving you time and money!