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photo of colorful fall leaves

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It’s time for your Fall Furnace Tune Up!  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 (same company as American Standard) and Coleman HVAC (same company as 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 Profressional Series gas & electric water heaters, and tankless water heaters.

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, and offer 24/7 Emergency Service.

Fall Gas Furnace Tune Up — Why It’s Needed

high efficiency gas furnace with two white pipes visible

Image Source: Dreamstime

A Fall Tune Up Ensures The Furnace Is Heating Properly & Safely

  • The Gas Furnace Tune Up checks many components of the furnace for proper operation.  A complete list of what is checked by Al’s Plumbing, Heating & A/C is at the bottom of this article
  • Also checked is if Cleaning Of Any Component Is Needed (some cleaning services may be an extra charge).  Cleaning dirty components ensures the furnace is heating at its peak ability & efficiency.

Example:  The Flame Sensor checks to ensure a flame exists while the gas valve is open.  If the furnace cannot determine a flame exists, it will shut the furnace down.  Without periodic cleaning, the Flame Sensor becomes so dirty it cannot detect a flame.  It shuts the furnace down to protect itself and you.

  • Most Furnace Tune Ups include an analysis of the combustion / exhaust-gasses.  This analysis will determine if further inspection of the Heat-Exchanger is needed.  We go into detail about this just below.

 

A Unsafe Gas Furnace Can Continue To Operate 

There Is No Safety Device On A Gas Furnace To Determine If The Heat-Exchanger Is Cracked. 

The Furnace Will Continue To Operate and Make Heat With A Cracked Heat-Exchanger. 

A Cracked Heat-Exchanger In A Gas Furnace Puts You At Risk Of Carbon Monoxide Poisoning.

Note: Electric furnaces do not have a heat-exchanger.

  • The burners create heat + exhaust gasses that pass inside the heat-exchanger.
  • The furnace blower fan moves your home’s indoor-air along the outside of the heat-exchanger.
  • If the heat-exchanger is cracked, exhaust gases can mix with the home’s indoor air.

photo of heat exchanger in gas furnaceImage Source: Dreamstime

SHOWN: New Gas Furnace Heat-Exchanger 

 

Click Here To See A Cracked Heat-Exchanger:  Photo Of Cracked Heat Exchanger

 

These Safety Devices Exist On Gas Furnaces 

Though perhaps appearing simple, a gas furnace is quite sophisticated.   A furnace has a computer type circuit-board (Furnace Control Board) that instructs the furnace to go through several safety checks during each heating cycle.  The furnace monitors for correct & safe operation the entire time it’s running.

Gas Furnace Safety Devices Are Typically Tested During A Furnace Tune Up

  • Control Board:  Check Performance To Ensure It’s Working Correctly & Safely.

If the control board gets a message something isn’t working correctly & safely, the control board shuts the furnace down.  This prevents the furnace from; creating a gas explosion, catching on fire, or allowing carbon monoxide into your home (except if it has a cracked heat-exchanger — described above).

Click Here To See A Gas Furnace Control Board: Photo Of Furnace Control Board

 

  • Flame’s Sensor:  Are The Burners Ignited?  What the furnace does if burners did not light.  If the burners don’t ignite, the Flame Sensor tells the furnace control board, and it shuts the gas off & shuts down to avoid a gas explosion.

close up photo of gas furnace flames

Image Source: ShutterStock

Shown: Property Ignited & Operating Burners Will Be Mostly Blue And Burning Within A Confined Area

  Click Here To See A Gas Furnace Flame Sensor: Photo Of Gas Furnace Flame Sensor

 

  • Flame Rollout Switch: Are The Burners’ Flame Only Where They Are Supposed To Be?  If the flames are outside their correct location, this is called Flame Rollout.  This can cause a fire.  The Flame Rollout Switch is designed to detect this problem and shut the furnace down.

photo of properly working gas burners in a gas furnace

Image Source: ShutterStock

  Shown: Gas Furnace Flames Correctly & Safely Within Their Proper Location

Click Here To See A Flame Rollout Occurring In A Gas Furnace:Photo Of Flame Rollout In Gas Furnace

Click Here To See A Flame Rollout Limit Switch: Photo Of Gas Furnace Flame Rollout Limit Switch

 

  • Is The Furnace Getting Too Hot?

If a furnace gets too hot, it shuts down to protect itself and you.  If it continued to get hotter & hotter, it could cause on fire.  To ensure this does not happen, a Gas Furnace Limit Switch checks the temperature of the furnace during each heating cycle.

What could cause a furnace to get too hot?  The most likely thing would be a failure of the furnace’s gas-pressure controller.  If gas enters the furnace at a pressure higher than the burners are designed for, the flames will become larger and can cause the furnace to overheat.

There is a whole-house gas-pressure regulator (attached to your gas meter outside) that ensures the gas enters the home at the correct pressure.  BUT, that pressure is  based on the total number of gas burning appliances your home has.

A home with a gas: furnace, water heater, fireplace, clothes dryer, & cooking appliances requires a higher gas pressure entering the home to ensure all these items can be running at once and have enough gas pressure for each of them.  If the home had only a gas furnace, the home’s gas-pressure regulator could be set to what the furnace requires.

Your furnace also has a gas-pressure regulator.  As with every component on the furnace, it could fail and stop working.  If that were to occur (and the house’s gas pressure is higher than what the furnace requires) the burners’ flames will be too large and it will overheat.  In this case, the Furnace Limit Switch would sense the overheating condition and shut the furnace down to protect itself and you.

Click Here To See A Gas Furnace Limit Switch:   Photo Of Gas Furnace Limit Switch

 

  • Are Exhaust Gases Being Vented Outdoors?

A gas furnace Pressure Switch checks to ensure the electric exhaust-gasses fan is running (this fan is often called “Draft-Inducer”  It checks to see if the pressure dropped (within the exhaust section of the furnace) because the exhaust-gasses fan turned on.

Once the Pressure Switch has confirmed the exhaust-gasses fan is running, it allows current to pass to the burners’ ignitor.   If it does not allow current to the burners’ ignitor, the furnace won’t allow gas to the burners.  Then the furnace shuts down until it’s repaired.

The exhaust-gasses fan is not running, the exhaust gases would enter the home and cause carbon monoxide to build up.  Carbon Monoxide will make you ill in smaller doses.   In a larger dose, it can kill you.

Click Here To See A Gas Furnace Pressure Switch:  Photo Of Gas Furnace Pressure Switch

 

What A Combustion / Exhaust-Gases Analysis Checks

Often described by different names, a “Combustion-Gases Analysis” checks for: Carbon-Monoxide, Ooxygen, & Carbon-Dioxide levels in the furnace’s exhaust.   These readings have normal ranges.  If any of these 3 gases is out of normal range, something is wrong with the furnace and it’s not operating correctly (and possibly not safely).

A Prime Example: If the heat-exchanger is cracked, some of the home’s indoor-air can be forced into the combustion-chamber (while the blower fan is running).   If this occurs, an Exhaust Gases Analysis will show too much oxygen.  This alerts the Furnace Tech that the heat-exchanger may be cracked.  Further inspection of the heat-exchanger is required.

NOTE:  This Analysis can also indicate when the heat-exchanger is NOT cracked.

NOTE: When oxygen is being forced into the combustion-chamber, it will distort the burners’ flames + change their color from nearly all blue to lots of yellow.

Click Here For Futher Details About A Cracked Heat-Exchanger:  AlsPlumbing.com Signs Your Gas Furnace Heat Exchanger Is Cracked

1. This Video Shows Furnace Burners’ Flames Changing From Mostly Blue To Lots Of Yellow Once The Blower Fan Turns On:  

Click Here For A YouTube Video — Burner Flames Color Changes & Distortions Due To Cracked Heat Exchanger

Note:  You also see the flames becoming distorted due to air entering the combustion-chamber through the cracked heat-exchanger.

 

2. This Video Shows Using Combustion-Gases Analyzer To Test For A Cracked Heat-Exchanger.  

(In This Video The Exhaust-Gasses Test Shows The Heat Exchanger Is NOT Cracked)

 Click Here For A YouTube Video: Combustion-Gases Testing / Analysis

 

Why A Heat-Exchanger Cracks

Metal expands when heated & contracts when it cools.  This recurring expansion & contraction is part of a normal furnace heating cycle. All heat-exchangers eventually fail due to metal fatigue (though they are often still ok when the furnace is worn out).  There is no way to determine how long a heat-exchanger will last, as many factors come into play.  The largest factor is typically how much the furnace gets used.  One home may have the heat set to 60 during the day (while owners are at work) while another home is always occupied and the heat is kept at 75 all the time.

A cracked heat-exchanger is not the only reason why it may make more sense to replace the furnace than repair it.  The heat-exchanger can be ok, but other expensive components (such as the control board or blower fan) haved failed.

 

Replacing expensive components on an old furnace may not be wise because of the age of all the other components.  After replacing an expensive component in an old furnace, the likelihood that another expensive component can fail later is a key factor in the repair or replace decision.

One Definition Of “End Of Life” For A Furnace:  If the furnace is older than 2/3 of its normal lifespan (normal lifespan for a gas furnace in DFW is 15 years), and the cost of repairing it exceeds 1/3 of the cost of replacing it, careful consideration should be given to repairing versus replacing.

NOTE: Heat Exchanger Warranties Are Longer Than For The Rest Of The Furnace.  Example:  American Standard Gas Furnace Heat-Exchanger Warranty Is 20 Years (part only).  The (parts only) warranty on the rest of the furnace is 10 years if the warranty was registered.

An older furnace may still have its heat-exchanger under warranty.  If this is the case, replacing the heat exchanger may be the best option. That depends on the charge to install the replacement heat exchanger + the age of the furnace.  The heat-exchanger warranty is for only the part.  You must pay to have it installed.

Some factors that can accelerate heat-exchanger failure.  These factors are usually:

dirty air filter on left. New air filter on right.

Image Source: CanStockPhoto

  • Not changing air-filters when needed.  This reduces air flow, causing the furnace to work harder and longer.  This accelerates wear-out of the heat-exchanger.
  • How Much The Furnace Is Used.  As with everything, the more something is used the faster it will wear out.
  • Poor Furnace Maintenance
  • Incorrect Furnace Installation
  • Furnace Design

Steps In A Gas Furnace Tune Up

  • Inspection: A technician inspects the furnace, tests it for proper operation and checks for any problems needing repair.stem from time to time.
  • Cleaning: Clean components (if needed) . A technician can remove any accumulations (additional clean charge may apply).
  • Adjustment: Checking for and correcting loose components plus other minor repairs (if needed).

These Items Are Part Of Typical Furnace Tune Up

  • Check Thermostat
  • Inspect Furnace Control Board and Test For Proper Operation
  • Inspect Gas Supply Line & Gas Valve
  • Verify Proper Burners Ignition
  • Check & Record Temperature Rise
  • Clean Burners & Adjust For Maximum Operating Efficiency
  • Clean The Flame Sensor.  A dirty flame sensor is one of the primary reasons a furnace shuts down.  Often this occurs during peak heating season.
  • Inspect Primary Heat-Exchanger
  • Inspect Secondary Heat-Exchanger (this extracts heat from exhaust gases in a high-efficiency furnace)
  • Inspect & Test Exhaust-Gases Draft Inducer Fan 
  • Safety Check All Controls For Proper Operation
  • Check For Gas Leaks (near furnace)
  • Test For Carbon Monoxide
  • Check Furnace Air Filter
  • Inspect Blower Fan Assembly Operation.  Lubricate & Adjust (if needed)
  • Check & Tighten Electrical Connections
  • Inspect & Clean Furnace Condensate Line (if needed)
  • Exhaust Gases Analysis
  • High Efficiency Gas Furnace Inspect Combustion Air Intake & Exhaust PipeS

high efficiency gas furnace with two white pipes visible

Photo Source: Dreamstime

Shown: 2 White PVC Pipes For High-E Furnace.  One pipe brings in combustion-air from outdoors.  The other removes exhaust-gasses to outdoors.

 

  • A Standard Efficiency (80%) Gas Furnace has one smaller diameter metal exhaust-vent pipe removes exhaust gases on 80% / standard efficiency furnace.  Standard efficiency gas furnaces draw combustion-air from the immediate indoor environment — directly into the furnace at the front.
  • Standard Efficiency gas furnaces draw combustion-air (from within the house) directly through vents at the front of the furnace.

Click Here To See A Standard-Efficiency (80%) Furnace:  Photo Of Standard-Efficiency Gas Furnace

  • An older gas furnace is less than 80% efficient.  It is identified by the one larger diameter metal exhaust-vent pipe.
  • Older gas furnaces draw combustion-air (from within the house) directly through vents at the front of the furnace.

old gas furnace

This Older Furnace Is Less Than 80% Efficient (today’s minimum efficiency).  It has a larger metal vent-pipe because so much heat is vented outdoors with the exhaust-gasses that gasses can rise out of the house without needed a fan to push them.

Today’s 80% gas furnaces exhaust no more than 20% of the heat made outside with the exhaust.  Their exhaust gasses are too cool to rise on their own, so they must be pushed outdoors with a electric blower (inside the furnace).

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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 (same company as American Standard) and Coleman HVAC (same company as 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 Profressional Series gas & electric water heaters, and tankless water heaters.

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, and offer 24/7 Emergency Service.