I recently received a call with the complaint of a 2-year-old furnace coming on but not staying on. The customer informed me that they had a company out and they said it was a dirty flame sensor and over-amping inducer motor. He cycled the unit and it was good. A month later, the same problem. This time she decided to change the batteries in the thermostat because they were low. Once again, it seemed to solve the problem!

A week later, the same problem. At the end of her ropes, she called me. After evaluating her system and hearing the full background of the history of the unit, we cycled the unit. I noted that the furnace would fire up perfectly and after about 10 seconds, shut the burners off and restart. To a rookie technician, this appeared to be a dirty flame sensor, to me, however, there was something more troubling going on here. Upon further investigation, I noticed that although it looked and acted like a dirty flame sensor, it was not.

For one, the flame sensor was already pulled and cleaned and did not solve the problem. The second reason I did not believe that this was the issue was that the control board was not showing a trouble code for a faulty flame signal. The control board was not showing any fault code at all until the unit cycled 8 times. After the 8th trial, it would lock out and show a lock-out code.

After taking in this strange scenario, I determined that all of the former repairs were just a coincidence that the unit would operate normally, and in fact, the unit had a bad relay on the control board. I went through every safety and sensor. I checked the gas valve and pressure from the inducer. All were within range. We replaced the control board and the unit operated properly. Six-month-long mystery solved! The moral of the story here is to take your time and don’t jump to conclusions prematurely. If the first tech would have noticed that the control board wasn’t showing any fault code, this could have caused him to dig a little further and saved this woman a lot of frustration! Too many times, I hear stories of customers purchasing products that end up not solving the problem. Youtube videos will only get you so far as well, the reason is that they are too vague and each trouble code has several different possibilities for the cause of the issue, and sometimes it’s not the most obvious. If you think you need some help so you don’t make a costly mistake, give our virtual technicians a call.

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