The article is about a gas furnace control board (its brain).  Al’s Plumbing, Heating & A/C in Plano, Texas provides maintenance & repairs for all brands of Central A/C, Gas & Electric Furnace, and Heat Pumps.  Additionally, we sell and install new HVAC Systems from American Standard (same company as Trane), Ameristar (owned by American Standard) and Coleman HVAC (owned by York HVAC).

Al’s also provides full-service plumbing maintenance, repairs and replacements for every plumbing component in your home.  Al’s sells and installs Rheem Professional Series gas & electric water heaters, and tankless water heaters.  Al’s is near your home in Plano, TX; Allen, TX; and Frisco, TX.  We service all homes in southern Collin and Denton Counties with no travel charges.

Call Al’s today to discuss any concerns or problems you have with your HVAC System or Plumbing.  We will arrange an appointment at your convenience.

Image Source: Pexels.com

A Furnace Control Board Is Quite Similar To Any Printed Circuit Board (shown) That’s In Any Personal Computer

This Is Part 1 Of A 3 Part Article About; Furnace Control Boards, How To Protect Them From Power Surges, + Other Ways To Minimize The Risk Of Early failure. 

• Part 1: Furnace Control Board – Purpose And Functions
• Part 2:  Power Surges Protection
• Part 3: Ways To Minimize Early Furnace Control Board Failure.

Click Here For PART 2 Of This Article: AlsPlumbing Furnace Control Board – Part 2

The Furnace Control Board Tells The Furnace Which Function To Perform

And In What Order

Image Source: DreamsTime

A furnace control board is its brain.  It’s much the same as any computer circuit board.   It operates all functions — and in the order they occur.  It controls everything the furnace does during each heating cycle.  Because they are sophisticated electronic, circuit boards — they can fail and must be replaced — and can be an expensive repair on a Hi-E furnace.   There are reasons why one might fail early.

Replacing a furnace control board costs up to $1,000, so it’s worth the effort to do what you can to ensure yours lasts as long as possible.  Within this 3-Part Article, you will learn about the more common causes of the failure — and how to extend its service-life.

A Furnace Heating Cycle

Image Source: ShutterStock

Shown: Nest Smart Thermostat

A Heating Cycle:

• The Thermostat calls for heat.
• The Induced Draft Motor turns on.  This fan removes exhaust gases to outdoors.
• The Pressure Switch senses the drop in pressure (caused by the Induced Draft Motor).  It tells the control board the pressure dropped.
• The Pressure Switch is a safety mechanism.  It ensures the furnace’s exhaust is being removed to the flue even before the burners are ignited.

• The Burners’ Igniter begins to heat up until it’s glowing orange.
• The Gas Valve releases gas to the burners once the igniter is ready.
• The Burners ignite.  They don’t receive a message from the board to ignite, rather they ignite as gas is released to them.
• The igniter turns off.

• The Flame Sensor senses the flame and tells the control board that a flame exists.
• If the Flame Sensor does not sense a flame, it tells the control board.  The board turns off the gas valve and shuts the furnace down.
• If the flame sensor doesn’t detect a flame — it’s typically because the sensor is dirty.
• The Flame Sensor is a safety mechanism.  It ensures a flame is burning while gas is being released.

Image Source: YouTube Embedded Video

Video Shows Furnace Burners Light For 3 Seconds And Go Off.  This is because the flame sensor’s dirty & doesn’t detect a flame, so the control board shuts the gas off.

• The (Flame) Rollout Switch monitors the burner’s flames to check that flames don’t extend beyond where they’re supposed to be .   If a Rollout switch senses an irregular or oversized flame, it notifies the control board.  The control board turns the gas off, and shuts the furnace down.
• Flame Rollout Switches are a safety mechanism.  They cause the furnace to shut down if they sense flames are outside the correct area.  If flames were allowed to burn outside that area, they would likely cause a furnace fire.

Image Source: YouTube Embedded Video

Click On The White Arrow In Center Of Image To See An Example Of Flame Rollout

You Can See Flame Rollout In The Image Above.  The Flames should be only large enough to fit through the holes in front of the burners.

NOTE:  Oftentimes, owners discover they have a cracked heat-exchanger during a “no heat” service call.  Their furnace shut down because air (coming through the crack in the heat exchanger) was blowing flames outside their designated area.  The rollout switches sent a message to the control board, and it shut the furnace down.

• The Limit Switch tells the control board the furnace is warm enough to turn the blower fan on.  It also monitors if the furnace is getting too hot.  It it’s too hot, the limit switch tells the control board.  The control board shuts gas off.  If will shut the furnace off temporarily (until it cools down) or completely (because overheating keeps occurring).

The control board turns the Blower Fan on.  The fan moves air through the furnace, removing the heat and sending it into the house.

• The Thermostat determines the home’s temperature matches its setting and tells the control board. The control board shuts off gas to the burners, then the induced draft motor, and finally the blower fan motor.  The heating cycle is complete.

The Control Board Also Helps Diagnose Furnace Problems.  

Image Source: YouTube Embedded Video

Click On White Arrow In Center Of Image To View Video

If The Control Board’s Light Is Blinking — Something Is Wrong With The Furnace

The small blinking indicator light on your furnace’s circuit board helps to diagnose the furnace’s problem.  The flashing light is visible through a tiny window on the furnace door.

The number of blinks between pauses corresponds to the furnace’s problem.  This number corresponds to a chart located somewhere on the furnace (usually on the removable doors on the front).

Example: “blink…blink…pause…blink…blink…pause…” would represent Item #2 on the chart.  The chart may say: “Ignition Failure” or “Pressure Switch Open.”

The Control Board Helps Protect Your Safety  

The control board monitors each of the furnace’s functions to ensure safe operation.  If it determines something is wrong, it shuts the furnace down to protect itself and you.

Example:  If the igniter fails, the furnace’s burners can’t light.  When heat is needed, the control board opens the gas valve for the burners and awaits an immediate message from the flame sensor that a flame exists.  If it doesn’t get that confirmation, the control board shuts the gas valve off and shuts the furnace down until the igniter has been replaced.

Al’s Plumbing, Heating & A/C in Plano, Texas provides maintenance & repairs for all brands of Central A/C, Gas & Electric Furnace, and Heat Pumps.  Additionally, we sell and install new HVAC Systems from American Standard (same company as Trane), Ameristar (owned by American Standard) and Coleman HVAC (owned by York HVAC).

Al’s also provides full-service plumbing maintenance, repairs, and replacements for every plumbing component in your home.  Al’s sells and installs Rheem Professional Series gas & electric water heaters, and tankless water heaters.  Al’s is near your home in Rowlette, TX:  Murphy, TX; and Wylie, TX.  We service all homes in southern Collin and Denton Counties with no travel charges.

Call Al’s today to discuss any concerns or problems that you have with your Heating & Cooling System or Plumbing.  We will arrange an appointment at your convenience.