Gas and Oil Home Heating Furnaces - burners won't stay lit
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blue3
11-10-08, 07:09 PM
I have an intermittent problem with my burners.
I have a 15 year old gas furnace with HSI. Digital thermostat. No problems until this year, after the yearly safety check.
My furnace runs normal for a period of time. At some point, I notice it short-cycles (burners light, go out, then relight), so I turn the t-stat down for a period of minutes to hours. After a period of time, when I try to turn the heat up, the furnace goes back to normal. It does not show any error codes (i.e. limit switch). It also does not go into lockout.
I think the only times this has happened is in the mornings, so presumably the higher call for heat overnite is triggering the problem.
From what I understand, this burner situation (short cycling) can be due to a bad/dirty flame sensor. I replaced mine.
Or a limit switch tripping. This kind of makes sense to me, because I can get the furnace back to normal after a period of time - as if it needs to cool off. But I did carefully check the furnace during the short-cycling (while the burner was out) and the metal over the burner and around the heat exchanger was NOT hot to the touch. Perhaps it had already cooled down.
Also, my unit is supposed to show an error code for a tripped limit switch, which it hasn't. IF it is tripped, will the burners still be able to even ignite? I am in the process of figuring out how to test the limit switch.
Finally, I wonder about airflow. I have been using washable-media filters that are many years old. This year I replaced one of them with a Filtrete paper/electrostatic filter. I can't imagine a new filter would be a problem, but maybe the different media has a different flow rate, and/or the old filter is too dirty? Should I think about other airflow obstructions?
I did have the system re-checked but by the time the tech got here it was back to normal so he suggested the flame sensor.
I have a 15 year old gas furnace with HSI. Digital thermostat. No problems until this year, after the yearly safety check.
My furnace runs normal for a period of time. At some point, I notice it short-cycles (burners light, go out, then relight), so I turn the t-stat down for a period of minutes to hours. After a period of time, when I try to turn the heat up, the furnace goes back to normal. It does not show any error codes (i.e. limit switch). It also does not go into lockout.
I think the only times this has happened is in the mornings, so presumably the higher call for heat overnite is triggering the problem.
From what I understand, this burner situation (short cycling) can be due to a bad/dirty flame sensor. I replaced mine.
Or a limit switch tripping. This kind of makes sense to me, because I can get the furnace back to normal after a period of time - as if it needs to cool off. But I did carefully check the furnace during the short-cycling (while the burner was out) and the metal over the burner and around the heat exchanger was NOT hot to the touch. Perhaps it had already cooled down.
Also, my unit is supposed to show an error code for a tripped limit switch, which it hasn't. IF it is tripped, will the burners still be able to even ignite? I am in the process of figuring out how to test the limit switch.
Finally, I wonder about airflow. I have been using washable-media filters that are many years old. This year I replaced one of them with a Filtrete paper/electrostatic filter. I can't imagine a new filter would be a problem, but maybe the different media has a different flow rate, and/or the old filter is too dirty? Should I think about other airflow obstructions?
I did have the system re-checked but by the time the tech got here it was back to normal so he suggested the flame sensor.