When this happens the heat exchangers rust and plug up and or fall apart. This furnace was in a farm home that was occupied by my parents before they passed on. After Mom passed 4 years ago the house was left at 55 degrees most of the time with the exception of weekends. (It has become my lake home with no lake) We had been having trouble with the furnace when we started the heating season this year. The furnace would cycle and produce heat and shut down with no restart. The furnace man who had installed this furnace made a trip out to check it for us on October 15th and could not get it to act up. 2 weeks later the same thing happened. (the furnace had been left off during the week) He came out again and checked, this time the furnace showed its symptoms. He did further checking and determined that the air switch was not closing due to reduced air flow. He thought plugged air intake, no such luck. It appeared that the primary heat exchanger was plugged. He did not want to jump to hasty conclusions and wanted to call his furnace supplier tech support first. They backed him up on this and a decision was made to replace the furnace. When he removed it yesterday both heat exchangers were rusted out. It had been explained by him that they are finding this type of issue with furnaces in the homes of snowbirds (people who winter in warmer areas) when the thermostat is set low to save fuel. The furnace does not cycle enough to dry out the heat exchangers and rust takes over.
Look up the Lennox manuals on line to read it yourself.
Edited by Kurtee, November 09, 2017 - 07:44 PM.