Flame Rectification

Why Flame Rod Failures Occur and How to Stop Them
By:  Eric Shidell, HVAC Service Mentor

Plenty of HVAC service technicians be taught early on that cleansing a flame sensor is a typical upkeep observe and that neglecting this fundamental activity can result in nuisance burner shutdowns and no warmth calls.  Let’s look a little bit deeper into this example and look at how and why flame failures happen and how one can forestall them.

Throughout a traditional fuel burner sequence of operations, the ignition gadget will activate, (spark or scorching floor igniter) and fuel shall be launched to the burner.  When the gas / air combination reaches the ignition supply, flame will turn into established. 

One of many crucial security options of recent fuel burner ignition techniques is called “Flame Proving”.  This can be a methodology whereby the ignition controller is ready to acknowledge that the burner flame has been safely established.  This “data” informs the controller that it’s time to cease the ignition supply and that it’s secure to proceed with the burner “run” operation.  Within the occasion of an issue or failure to ignite, the flame proving system will shut down the stream of fuel to the burner.

Issues that happen with the flame proving system can lead to a nuisance shutdown of the burner system.  This ends in a no warmth scenario.

How it works:

A quite common methodology of proving flame known as “flame rectification”.  A particular steel rod is mounted within the path of the flame.  This is called a “flame sensor” or “flame rod”.  Flame rods are discovered on almost all induced draft burner techniques and on many compelled draft burners.

In a nutshell, the flame rectification system is {an electrical} course of that causes a low stage DC present to be performed from the flame rod via the flame, and again to floor.  Technicians can measure this flame present by putting a meter that measures DC microamps in sequence with the flame rod.

The ignition controller is programed to search for this DC present and make a “go – no – go” determination primarily based on the power of this present.  Regular flame present values for induced draft burner techniques will range between producers and system kinds.  A traditional sign power between 1 microamp DC and seven microamps DC is widespread.  If the flame present is just too low, or not current, the ignition controller will cease the ignition operation and cease the stream of fuel.  This prevents the potential of explosion.

Two of the nice strengths of this method is that’s has very quick response (inside microseconds) and it’s unattainable to bypass or defeat.  One of many weaknesses is that the quantity of flame present may be very low and will be diminished pretty simply.  

Because the flame rod, the flame, and the steel elements of the burner and manifold are all a part of a really low energy electrical circuit, they’re topic to the identical issues that each one electrical circuits are topic to.  As these elements turn into soiled or rusty or corroded, {the electrical} path turns into corrupted and the flame present will be diminished though the flame has been efficiently established and every little thing is working usually.

This ends in a nuisance shutdown or lockout and a no warmth scenario.  On this situation, you’ll observe the burner undergo its regular ignition sequence, ignite the flame, after which shut down inside seconds.  Some burners will go right into a retry mode and repeat the method plenty of occasions.  Others will lock out till an influence reset.  For the transient interval that the flame is lit, it is possible for you to to measure the flame sign and see that it’s weak.

This shutdown is a traditional response to a low flame sign.  The ignition controller is doing its job and dealing to maintain issues secure.

What  to do:

Flame rods don’t usually have to be changed except they’re bodily broken or damaged not directly.  To appropriate this situation, the flame rod must be cleaned in addition to the burner tip.  The standard of flame must also be verified as a poor flame that’s lazy or lifting off the burner can even interrupt the flame rectification circuit.  The identical goes for the flame rod electrical connections and the bottom connections.

Flame rods must be cleaned with a stiff metal wire brush or metal wool.  By no means use sandpaper, plumber’s roll, or every other abrasive.  This can scratch the floor of the flame rod.  As soon as cleaned on this means, the contaminants will shortly fill within the scratches, inflicting the flame rod to foul once more in a short time.  A scratched up flame rod must be thought of broken and it must be changed. 

The underlying trigger:

The underlying explanation for a fouled flame rod is definitely contaminated combustion air.  Fuel burning home equipment that acquire all of their combustion air provide from indoors are extra prone to nuisance flame failures than these put in in ventilated attics, crawlspaces, outdoor, or people who use out of doors air for combustion.

There are lots of chemical contaminants to indoor air. When these chemical compounds are burned within the flame they may go away a virtually invisible insulating coating on the flame sensor.  That is what results in low flame sign.  Frequent culprits are:  Cleansing provides, Laundry detergents and material softeners, Cat litter bins, Pet meals, Everlasting wave options, Pool and spa chemical compounds, Fertilizers, and others.  

The most effective long run resolution to nuisance flame failures and soiled flame sensors is to seek out and take away contaminants from the combustion air provide.  It could be essential to pipe in clear outdoors air for combustion into the equipment enclosure, or use a direct vent equipment that makes use of outdoors air for combustion.

Understand that whereas cleansing a flame rod is a reasonably simple repair, there may be typically extra to the story.  That represents a possible to show your data of the underlying explanation for flame rod failures right into a long run resolution on your buyer and extra work on your firm.

Try the hyperlink to my YouTube channel for extra ideas, tips, and troubleshooting movies and take a look at the The HVAC Know It All podcast right here or in your favorite podcast app.  Completely happy HVACing…

Eric Shidell bio

Eric Shidell is a veteran excessive stage HVAC service and diagnostic technician and knowledgeable mentor and coach.  He’s a pioneer of distance studying for the mechanical trades.  He helps HVAC contractors throughout North America improve the efficiency of discipline technicians via intermediate and superior technical coaching applications.  Study extra at www.hvacservicementor.com or e mail Eric at [email protected].  Contact by cellphone at 719-425-9860.