Had a no heat call today on a system I was at a month ago for regular maintenance and found today that the flame sensor was dirty I was reading .2 ua so I cleaned the flame sensor check my ua and it was back up to 2.8 after cleaning my problem with that though was that I cleaned the flame sensor on the maintenance call and was reading 2.8 ua after cleaning it then as well I got to looking at the work history on this call and saw that our company (i have only worked with this company for the past 7 months) has been out there 3-4 times a year cleaning this flame sensor and has even been replaced twice any suggestions as to why this may be getting dirty so quick so I can get this problem resolved and keep a good loyal customer from getting angry with the company
What is the gas pressure set at? Cleaning a flame sensor with anything abrasive is a bad idea. I use a shop rag or the flap of my cargo pocket. It doesn't take much to remove the buildup...unless someone cleaned it once with a wire brush or sand paper and now it is corroding. I would replace the flame sensor and start fresh.
The flame is conductive and the circuit is between the flame rod and the burner. So be sure to clean the metal parts of the burner near the flame rod so you get good current. You should also put a meter in series with the flame rd and see what your getting.
I have a 2 stage Ruud furnace that once a month amber light blink clean it and I comes back in a month later replaced sensor now gonna change the board this is direct vent to outside 12 ft above the ground
Do you mind if I ask exactly what brand and model of furnace this is. I ask, because over the years, at times manufacturers have had service bulletins, and changed components for exactly the reasons you have described, which has included flame sensor changes, relocation changes, and ignition module/circuit board changes. Myself or other members here might be able to help you if we have the exact unit you are referring to. If not, have you called the manufacturer tech support to see if they have made changes.
I was once told never to use grit cloth on a flame sensor because they use silicone in the manufacturing process to hold the grit on the paper. So then over time as the rod heats up the coating hardens and acts as an insulator and interrupts the flame signal. I'm not sure how true this is but it makes sense.
Glenn thanks for the reply I have spoke with tech support they pretty much said I'm on my own I do believe that it is something in the air just not sure what it is or how do cure it but I wanted to ask on here to see if anyone else may have ran into it and what they did to repair it instead of a monthly bandaid everything has been helpful so far
Jesjen I have always looked at it like this, and also been told when I first started in the field and have always felt it is right but how it has been explained to me is you don't want to use any type of sand cloth on a flame sensor because it will leave sand residue and when sand becomes extremely hot it can become glass and glass in this instance would act as an insulator on the bare metal of the flame sensor and keep it from properly rectifying the flame signal not sure if its completely right but I can see how that would happen
That is exactly correct tkhvacguy. The other thing that happens is the sand cloth cuts "v" shaped grooves into the rod, creating little valleys that can fill with the sand, leading to an even thicker coating of "glass" on the rod. The more often it gets cleaned with sand cloth, the worse the condition can become. How about a reply to Glenn's request of brand, model and serial?
Have you verified that the furnace is well grounded not only at the flame sensing circuit, but all the way back to the electrical panel?
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