I have a Lennox 023Q5-140 oil furnace, with forced air, which is approx. 10 years old. Lennox told me that it is a 5 Ton 2,000 CFM unit.
Last year the heat stopped and the mechanic found the high-limit switch was open. He removed the switch and it reset itself. He then found that the limit switch was frequently tripping and a few minutes later resetting itself. This is apparently unusual as the limit switch should only trip in rare cases as a safety valve. Is this correct?
The mechanic found the total static pressure was 0.84-0.9" WC. He felt that poor air flow at the heat exchanger was causing the limit switch to trip so frequently.
The mechanic told me that I should replace my limit switch as it failed once and is overused by tripping so frequently. If it failed again in the open position, I could have no heat again. If it failed in the closed position, I could have a major problem. Is this correct?
As I understand, the furnace is suffocating and overheating due to insufficient air flow. The mechanic told me that I should modify the return air duct so more air gets to the burner. Lennox agreed and said this is to protect the limit switch, heat exchanger, etc.
The "cut-in" between the main air return trunk and the furnace is 22" x 14" and I use standard (NOT high efficiency) 16" x 25" disposable filters.
This sounds expensive, including a larger hole into the furnace, larger air filter, and maybe a larger main air return "trunk". Could you please clarify the need for this and what should be done?
These repairs make sense, however the furnace has worked fine for the last year, although I don't know if the limit switch is tripping frequently or not. It also has been working for 10 years with no problems other than this and an unrelated circuit board problem. So why should I do anything? Maybe just let it be?
Thank you very much.