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Saturday, 28 January 2012 17:17

Solving Common Gas Furnace Problems

Written by Eric Noack
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Solving Common Gas Furnace Problems

Hi, my name is Eric Noack. I'm an HVAC technician at ABC Plumbing, Heating, Cooling, and Electric.  In this month's blog article I'm going to talk about some of the most common gas furnace problems we encounter and some of the things to look for when your gas furnace is not heating properly.

The following are some of the topics covered in my series of videos on furnace problems at About.com.

Thermostat Problems

The first thing to check is the battery. Most digital thermostats have a battery indicator on the display. If you see an icon in the display asking for a battery, follow the manufacturer's instructions and replace the battery with an appropriate size.

If you see no display at all, check the power to the furnace. This particular thermostat has a sealed battery in it, and it's not replaceable.

If you've checked the battery, you've checked the power supply, and your thermostat is still not operating properly, it's likely that you're just going to have to replace your thermostat. It's important to understand how your thermostat operates when it's normal, when everything is right. If you're familiar with the proper operation of your equipment, then it's going to make it easier if you notice something acting unusually and you can call ABC a proper diagnosis.

Mismatching Furnace and Thermostat

Your home's gas furnace needs to be paired with the correct thermostat to work properly; if it isn't, you could run into problems.

Thermostats have to be matched to the system based on the type of furnace that's used and the capacity and capability of that furnace. The best way to make sure you're going to have a thermostat that matches your system is to get it from an HVAC professional.

Electronic Ignition Furnace Problems

To determine what type of ignition system you have, open the front of the furnace and initiate a call for heat. Observe what happens in the burner area. If there's a very small flame that starts first, and then ignites all of the main burners, that's an intermittent pilot type of ignition. If the ignition happens and the main burners come on immediately, then that's a direct ignition.

Once you determine which type of ignition system you've got, if you see it operating in a way that's not correct, it's best to call an ABC service technician as soon as possible. It's important that your are is aware of how the 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. It's going to help maintain the equipment, keep it lasting longer, keep it safe, and also reduce your energy costs.

Furnace Has a Noisy Operation

Squeaks, rattles, and rumbles are some of the things that we hear from furnaces. In the case of a squeak, it can be related to a motor failing or just making noise. Rumbling and rattling can be caused by an out of balance blower wheel caused by debris or just age or just being dirty. 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.

Squeaks and squeals can also happen from air leaks. There can be a leak in the duct work or around the furnace somewhere that's allowing a small amount of air to leak in or out causing a whistling or squeaking sound. If you suspect that a high-pitched squealing or whistling noise could be coming from the air flow, what you want to do is check some of the gaps or joints where the sheet metal is connected. Those are the likely sources where that can happen and it can be simply sealed up with tape or a piece of putty or something like that. Sometimes something as little as this door being out of alignment can cause a squeal or a squeak and you can just move it a little bit or just make sure it's firmly placed where it should be.

So when you look at the burners on a furnace, you can kind of judge the condition. If you see any kind of dust, lint or other kind of dirt in the furnace, that could be clogging one of the burners and causing excess noise in a furnace. In that case, it's really important to get a professional out to do a proper cleaning on the furnace for you. Knowing a little bit about your system and being educated about it is the best way to stay on top of it and avoid breakdowns. A lot of times when homeowners hear the system operating in an unusual way, they can have us come out and take care of it before it becomes a bigger issue.

Furnace Blower Does Not Turn Off

The first thing to check is the fan switch on the thermostat. "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 "low," "medium," or "high," then you're going to have continuous fan operation.

The next thing to look at is your furnace filter. If you find a 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.

Furnace Cycles On and Off Too Frequently

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.

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.

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.

Furnace Does Not Produce Enough Heat

One of the most common sources of this kind of problem is a clogged filter. It's very important that you check your filters regularly and change them frequently for good furnace operation and best efficiency. The second possibility is that the furnace was not sized properly, meaning that it doesn't have enough capacity to keep the home warm. It's important that a heating and air company size the equipment for the capacity needed to keep your home warm. Another possibility, though it's pretty rare, could be that your burners could be clogged to the point where it's not allowing the furnace to create enough heat and meet its full capacity.

Furnace Does Not Heat

Some possible causes of that are: thermostat not adjusted properly, the power going to the furnace could be shut off, the gas going to the furnace could be shut off, or the pilot light could be out. A couple things to check with the thermostat: Now, the first thing to remember is that everybody's thermostat is going to be different. In this case, when the red light is on, that means that it's in heat mode, so it's ready to heat the house. The next thing to check is to make sure the set point is higher than the room temperature. So if we raise that set point above the room temperature, that's going to turn the heat on.

Furnace Pilot is Out

Some of the common sources of a lost pilot light are a failed thermocouple, a strong draft, or a clogged orifice to the gas supply to the pilot light. A thermocouple is a device on a standing pilot system that proves the flame to the gas valve and allows gas to keep flowing as long as there's a flame sensed. It's probably best if you have a professional check it out, clean it and verify that it's working properly. Now, the thing to keep in mind is most modern furnaces don't use a standing pilot light anymore.

Last modified on Saturday, 28 January 2012 18:12
Eric Noack

Eric Noack


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