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The code I have been getting is the alternating slow flash - watchguard. burners failed to ignite or lost flame 5 times during heating cycle. I have already cleaned the flame sensor but it still fails to ignite. If I turn the main power switch off for 10 seconds and then turn it back on, the furnace operates as normal - no problems igniting and running. This only last for a few hours however. Any ideas?

Thanks.

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  • Flame sensors can get squirrely and function erratically as the age. It may be time to replace it.
    – HoneyDo
    Commented Feb 16, 2023 at 20:48
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    Welcome! You'll have to monitor the furnace manually to see what's really happening, and describe it to us carefully: does it truly fail to ignite when the gas valve opens, or does it sometimes extinguish even though the gas valve is being held open, or is the problem one of mis-detecting when there is or isn't flame? The latter is evidenced by flame reliably igniting when the gas valve opens, but then the valve closes abruptly while the thermostat is still calling for heat.
    – Greg Hill
    Commented Feb 16, 2023 at 21:07
  • Do not know much, but having basically a reboot fix the furnace for a short period of time, might point to a problem with the control board more than a sensor/valve part.
    – crip659
    Commented Feb 16, 2023 at 21:18

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My first thought is that the igniter is going bad and failing to ignite every time. It may also be a limit switch either going bad or noticing that it's not igniting fully or quickly enough and causing the system to stop or start the process over. If it's a limit switch, the power off might be resetting it, which is allowing it to work once before having issues again.

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