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Video:How to Fix a Gas Furnace: Furnace Blower Does Not Turn Off

with Erick Noack

If the blower in your gas furnace won't turn off, it can cause major problems with your home heating system. Here's a video with instructions for fixing a gas furnace where the blower won't turn off.See Transcript

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Transcript:How to Fix a Gas Furnace: Furnace Blower Does Not Turn Off

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 what to look for if the blower motor won't shut off on your gas-fired furnace.

Thermostat Affects Blower in Gas Furnace

So some of the things that you might look for if the furnace fan is running continuously, first of all is the switch on the thermostat. The first thing that 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.

Check Filter

Next thing that's important to look at is your filter. If you find a severely clogged filter, it may have caused damage to the limit switch. What the limit switch does is it senses the temperature inside the furnace. If it sees a temperature that's too high, then it shuts off the fire as a safety and only will allow it to come back on once it's cooled sufficiently. If the filter has been clogged for too long, then it may have damaged that switch to the point where it needs to be replaced. In this case, the furnace high limit is a small button type device that's got two wires connected to it. Every furnace is a little bit different. Some of them have more than one limit, and some of the limits look very different. If that limit switch is failed, it's very important to find the source of why it failed and not just replace the switch. It's a very important safety issue. It's best to have an experienced, qualified technician check that out.

How a Filter Affects the Blower in a Gas Furnace

If a filter becomes too clogged, what happens is it restricts the air flow through the furnace, so the furnace is working too hard to move the heat away from the furnace. In some cases, the furnace fan will run continuously until that safety switch closes again. That's an indication that the furnace has overheated, and it needs to be taken care of. When you remove that filter, if it's a disposable filter and pieces tear off of it, they can get caught in the blower wheel. And that can throw that wheel out of balance and make a lot of noise. It's important that a homeowner is aware of the way his system is supposed to operate when everything is normal. So that way when things do change, you can be aware of it and call for service before it becomes a bigger problem. The other important thing is to check and change your filters frequently. This is going to help reduce your energy costs, reduce potential damage to the furnace, and also help to keep the air in your house cleaner.

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