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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 6022
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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I have a Conquest 90 furnace in my house that is 10 years old.

Customer Question

I have a Conquest 90 furnace in my house that is 10 years old. A week or two ago, I noticed that while the furnace did still run just fine, it wouldn't run long enough to get the house up to the temperature on the thermostat. I thought the thermostat was the problem, so I replaced it yesterday, but I've still had the same problem since then. Is there something I can repair myself, or should I call a repair man?
Submitted: 6 years ago.
Category: HVAC
Expert:  Douglas replied 6 years ago.
Hi, I'm Douglas and I am here to help you resolve problems with your heating and cooling equipment.

It could be a number of things to start... It could be cycling on the limit switch.

In this case, make sure the filter is clean, and all the vents in the home are open and not obstructed.

Next, because it's a 90+ furnace it has a drain. If the drain is slow, water can back up into the furnace and trip the pressure switch. If you can blow the drain out you can see if that helps.

Other faults usually dont let it cycle like that. You can check the vent pipe outside to make sure it's not got anything blocking it such as leaves, a bird or rocks (kids put anything in them). But if it were blocked, it usually will not start well.