Flame Rectification: Grounding

Heating season is here, breakout the thermal underwear, dust off the heating tools, and brush up on heating system troubleshooting. Tis the season for 3am no heat calls. Oh, joy…
Every year more ancient furnaces and boilers are replaced, and every year you get more no heat calls that start out with- “The old unit ran fine for 30 years”. You install a new system and it doesn’t run a season without a malfunction.

How can you pull out a dilapidated old furnace that was on its last legs, put in the newest, most high tech system, and have continual problems? The answer may be easier than you think.

At least the new equipment has self diagnostics to tell you what the failure was. And wonder of wonders, it’s almost always one of two codes; high limit trip, or ignition failure. Today we’re going to talk about ignition lock outs.
Chances are the old system you replaced used a thermocouple or a thermopile to sense flame. The old furnace didn’t care if it had a ground or not. In fact, many old homes have electrical services with inadequate grounding or no ground at all. You can tell if there’s no ground at all, look at the outlets. If they only have two slots with no center ground, the home likely has no grounding. I know what you’re thinking “So what?”
What does grounding have to do with ignition failures? Flame rectification. Flame rectification is the flavor of the day for light commercial and residential flame detection, and guess what? It needs a quality, true-earth ground to work.
Flame rectification uses the flame to conduct electricity from the gas burners flame sensor to…you guessed it, earth ground. In other words: no ground = no flame sensing.

The picture above is from an actual site that was experiencing ignition failures every month or so; everything was setup correctly: the gas pressures were right on, the vent piping was perfect, and the ground at the furnace was secure.
A trip into the home’s crawl space revealed the little gem in the picture; a rusted junction box with a ground that was hanging on by a thread. The juction box and grounding was repaired by an electrician, and the system hasn’t had a hiccup in three years.
Remember, the ground at the furnace may be good, but don’t forget the electrical box or the actual ground rod outside the home; a good ground is “good” from the furnace all the way to the actual ground rod.
If you have any questions at all about the condition of the homes service or ground, call an electrician. Or as I like to say- “When in doubt, call sparky out”

Patrick is Zen HVAC’s diagnostic and training guy. Patrick started in the trade the day he left technical school and never looked back. He's served in various technical and training roles in the HVAC industry but specializes in system troubleshooting and diagnostics, retro commissioning, and technical training. His moto: If I can understand it, anybody can. Patrick uses the Zen common sense approach to teach Patrick’s Likes- His Wife, kids and dog. Old pickup trucks. Hiking. The industrial Revolution. Patrick’s Dislikes- Taking work too seriously. Anything unintuitive. Emoticons :( Patrick’s Favorite famous person- Theodore Roosevelt “I am only an average man, But I work harder at it than the average man" Famous Patrick Quote- “Well, that was stupid of me”

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