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Video:How to Fix a Gas Furnace: Furnace Goes On and Off Too Frequently

with Erick Noack

If your gas furnace is turning on and off too frequently, there are a few things you can do to fix it. Here is a video explaining how to repair a gas furnace that turns on and off too frequently.See Transcript

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Transcript:How to Fix a Gas Furnace: Furnace Goes On and Off Too Frequently

Hi, my name is Erick Noack. I'm an HVAC technician for ABC Plumbing, Heating, Cooling, and Electric. And we're here for About.com. Today I'm going to show you a couple things you can check if your gas furnace is short cycling or turning on and off too quickly.

Check Thermostat if Gas Furnace is Short Cycling

If you notice the frequency of the heat cycles becoming too short, that's an indication of a problem with your system. The first thing you want to check is the fan switch on the thermostat. In this case, it's up here in the display and it says "auto." Now, "auto" means that the fan should only be running to try to heat or cool the home to try to match the thermostat setting. If you see the thermostat fan switch set to "on," or in this case "low," "medium," or "high," then you're going to have continuous fan operation.

Filter May Cause Furnace to Short Cycle

Next, I'm going to show you how to check the filter. If your filter has been in the furnace for a long time and its gotten very clogged, it can cause the furnace to what we call cycle on limit. That means that instead of heating continuously, the flames turn on and off because the unit is overheating due to that clogged filter. You remove the cover and that exposes the edge of the filter right here. This one is a washable filter, so it's got a little tab that you use to pull the filter out. It's going to trap dirt on one side and let the clean air come through on the other side. The important thing with filters is watching the air flow direction. There's always an arrow that tells us which way the air should flow through the furnace. On most furnaces, people have drawn arrows that tells you which way the air flow direction should be. This filter is a washable filter, so you're going to want to follow the manufacturer's instructions for cleaning. Make sure that the filter is completely dry before you re-install it. In some cases you're going to be using water to rinse them out, you don't want to be putting water back into the furnace.

Disposable Filters

A lot of people use a disposable filter. The key point if you use a disposable filter is make sure that when you pull that filter out all the parts are there and it didn't tear or leave any pieces inside the furnace. When you use a disposable filter, change it out, put a new one back in there. I always recommend writing the date on the side of the filter, that way you know how long it's been in the furnace.

Blower on Gas Furnace Should Be Checked by a Professional

Early gas furnaces used a motor with a belt to drive the wheel. That's the blower that moves the air into the house. All modern furnaces use a direct drive blower that's permanently lubricated. It doesn't require any lubrication or maintainance on that. The way to identify the difference is when you look down into your blower compartment of your furnace, you're going to see your blower housing and you can follow the wires up to the housing. If you see the motor centered in that blower housing, that tells you it's a direct drive blower. On earlier model furnaces, with a separate motor, belt drive, and blower wheel, it did require some maintainance to that belt and lubrication. That's something that's best left to a professional. Another possible cause of short cycling or furnace turning on and off too quickly can be too many register dampers closed. You want to make sure those dampers are wide open and allowing air to flow freely.

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