Hi everyone can anyone tell me about what might be wrong with this furnace it's a armstrong ultra 5 enhanced 95v. we had a repair guy out because it will not stay lit he said it was the flame sensor ,first he cleaned it and he charged my dad $136.00 to come out and find the problem and $88.00 to clean this rod, two days later my dad started the furnace because he has a pellet stove that he uses most the time and the furnace would not stay lit, when the furnace repair guy came back he said that the flame sensor rod was now bad and he would put a new one in for $196.00 but he would not charge to install it. we told him no and we went up to heating and air supply place in town and the flame sensor part was a total of $11.00 but it looks a little different, it's the same length but where the ceramic part is at the top it's just longer but we gave all the numbers to the lady at this place and she said that was the right one but the furnace still will not stay lit. I installed it and at start up the burners do lite but only for about 3 sec. that's it and on the circuit board the Leds blink 4times and in the book that came with the furnace it say's open thermal protection switch, but at one point when the furnace was trying to lite the led had a continuous flash and the book said a flame signal sensed, out of sequence. so now I cleaned the old flame sensor rod and it's in there now and it still won't stay lit. This furnace is about ten years old just to let you know. so I thought I would ask one of you guy's what you might think is the problem and if you think it's the thermal protection switch where is it located. if anyone can help that would be great! thank you for all the help. steve O
1. Flame signal need to be checked in series with the flame sensor measuring micro amps DC
2. 4 Flash code. Typically caused by restriction in duct system IE plugged filter or dirty evap coil or bad blower motor
3. Your furnace is know to have heat exchanger failures. Did the tech check for this before working on the system? The heat exchanger is what separates the fire and flue gasses from the air circulated through the house. Need to ensure the heat exchanger is intact.
4. it is possible that the control board is the culprit. check flame signal first. also check wiring harness plug ends to ensure good connection at the board and through the blower deck.
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