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Top 5 Furnace Problems and How to Fix Them

Top 5 Furnace Problems and How to Fix Them

We’re going to be showing the scenarios or the symptoms of what the furnace will be doing or not when you are experiencing problems.
But we want to point out one thing before we begin.
It is a must to switch off your furnace before touching anything for your safety. But before you switch your furnace off or reset the power, the first thing you want to do is look at your control board and find the led error code light.

Most furnaces will have this error light on them. It’s just a little LED light that’s either green or red. Oftentimes there’s going to be a sight glass on the door so you don’t even have to take the door off to see what it’s blinking and just write down or remember which code it’s blinking.
In most of the furnaces, the door or cover has blinking codes as a guide to the owners.
It will have short and long blinks so just count those blinks and write them down. For example, it’ll be two short blinks then pause and then there will be three long blinks then it’ll be a long pause, and then it’ll start over.
So, what happens is when you reset the power to your furnace, the little error code gets reset or cleared out. If it’s an intermittent problem, then chances are your furnace might start up and run fine for a little bit and you’re not going to know what the problem was because you just cleared that code out.
So, before you switch your furnace off, check the error code first and write it down.
The first problem that we’re going to go over is –
1.) Dirty Flame Sensor.
This one happens the most out of all the furnace problems but it is also the easiest problem to fix. The igniter will glow the flames.

But it just lit for about three or four seconds and later they just go out. That’s the symptom of a dirty flame sensor.
Whenever you see your furnace light very short, it’s almost guaranteed to be a flame sensor issue and what will happen is the furnace will typically try again three to five times.
It will keep trying to light and once it fails it will go into a lockout status for a few hours. The furnace will just sit there and do absolutely nothing and after the few hours of lockout status, it will start back up and try again.
After you write down the error code then switch it off, you open the top door or cover and turn your furnace on. Then see what the furnace does and see if the igniter lit for just three to four seconds.
After confirming the symptom, switch your furnace off again for your safety since you will be touching things inside to clean the flame sensor.

How to clean the flame sensor

Again, any time you’re reaching into the furnace and touching things, you should have the power off because there are electrical connections that could shock you if you touch them accidentally.
So, we have the igniter, that’s the thing that was glowing bright orange. Usually, the flame sensor will be on the opposite side of the igniter.

The flame sensor is held in there just by a quarter-inch screw and the flame sensor is just a metal rod.

It can be bent in two different positions. It could be like a 45-degree bend or it can just be a straight rod.

With time, build-up starts to form on the flame sensor and that’s what prevents it from actually sensing the flame.

If it doesn’t sense the flame, it turns the gas valve off and the flames go out. That’s what’s causing the flames to come on for only three seconds and then they turn right off.
To remedy this, all you have to do is simply clean the flame sensor with a Scotch Brite pad.

Even a dishwashing scrubby should work. Just press down real firm and clean that whole metal rod so that it starts to shine. Get all that build-up off of it and that should solve your problem.
After you cleaned it all off, put the flame sensor back in.
Usually, there’s only one screw hole so you can’t put it in incorrectly. It’s always going to be facing the right direction. Once in a long time, you do have to replace it but usually cleaning it is enough.
There’s one wire that goes to it.

It ends up right in front of the burner and then with the quarter-inch screw, just tighten it down.

After you get the flame sensor cleaned, you should be able to turn your furnace power switch back on and the flames should turn on for a lot longer than just three seconds.
2.) Dirty Air Filter
If you have your furnace set to 72 but it’s only getting to about 70 degrees and no higher if that keeps happening to you and you haven’t replaced your filter in a long time then we would recommend the first thing you do is to replace the furnace filter.

Most furnaces will have a high limit switch or a fan limit switch.

Just a black box or it can be a little cylinder-shaped or a round-shaped silver looking disc.

The function of the high limit is to turn the furnace off if it’s getting too hot in there and one of the reasons it’ll get too hot is because the furnace filter is plugged and there’s not enough airflow going past the heat exchanger.
If there’s not enough airflow then the furnace will start to overheat slowly. Once it overheats to a certain point, the flames will shut off and the fan will stay on to cool the furnace off.
The dirtier your filter is, the more often that will happen and just like the flame sensor, if this happens three to five times in a row during one heating cycle, this will cause the furnace to go into a lockout.
So, for three hours the furnace will just sit there and do absolutely nothing.
Sometimes, this is not very noticeable if it’s not very cold outside. You might not even notice that the furnace went into a lockout and it just sat there for three hours doing nothing.
Or maybe the furnace blower motor was on the whole time, some furnaces will do that and that masks as well so it would seem like the fan is running but the burners are not on.
So, if it’s not very cold outside, you might not notice it right away but once it gets colder outside that will become noticeable and your temperatures in the house will start to drop.
So, if your furnace is not keeping up, there’s a good chance that you simply have a dirty furnace filter. Once you replace that, that should solve your problem.

  1. Bad Inducer Motor.

The symptoms of that are simple.
Usually, if you’re experiencing this problem, you have your thermostat set to heat temperature bumped up, a lot of times your control board will be blinking a pressure switch open code and your furnace will be doing absolutely nothing.
For example, if you turn your power on, your thermostat is calling for heating but your furnace doing nothing. You might hear a little click means the control board sent power to the inducer motor.
Judging by that click, if you have a multimeter you can check if it has power. If your inducer motor is getting power but it’s not starting then the inducer motor is simply bad or there’s something stuck in the blower wheel inside.
A dead giveaway of a bad inducer motor though is if you put your hand on it and it’s very hot while your furnace is doing nothing then your problem is with the inducer motor.

If nothing is blocking inside the blower wheel then you might need to replace it. Once you replace your inducer motor you should be right back in business.

  1. Bad Blower Motor.

A lot of times, this will be accompanied by a burnt plastic smell or a burnt electric smell throughout the house. You’re probably going to smell it. So, oftentimes when we come into a person’s house and they tell us they smell a burnt electrical smell, it’s almost every time that the blower motor is bad.
If you cycle the power to your furnace, what happens is the burners will come on, your inducer motor running everything is fine and your blower motor should come on shortly after the burners light. About twenty or thirty seconds after the burners light, your blower motors should be coming out but if your blower motor is bad then of course it’s not going to come on.
You might hear it hum a little bit if it’s trying to start but it won’t if it’s bad.
What happens is the temperature limit that senses the temperature inside the furnace will sense that the furnace is getting too hot because the blower motor is not turning on at all and once that limit switch trips, the flames will extinguish and the furnace will wait until it cools off and that switch closes back up before it’ll try again.
So, let’s just see an example of that my blower motor is not going to come on right now
Once your furnace has been on for about one minute, the blower motor should have come on at least 30 seconds ago. If your burners are on for a minute or longer and your blower motor is not coming on then there’s a good chance that that blower motor is bad.
Another thing you can do is carefully grab the motor and feel it on the sides. Just like the inducer motor, if it’s very hot then most likely you have to replace that whole blower motor.

You can take that bottom door off on your furnace. Your blower motor is typically going to be on the right side but it can be on the left as well. Reach in there carefully and of course, your power should be off.
There is also a chance that the Control Board has simply not sent power to the blower motor and that’s what’s causing it not to turn on.
But if your blower motor is hot that means it is getting power and you for sure will have to end up replacing it.
The correct sequence of operation with it working normally will be – the inducer motor always comes on first and shortly after, the igniter will start to glow. The gas valve opens, all the flames ignite or all the burners light, and the blower motor will take about less than a minute to come on.
Depending on what furnace you have, your blower motor may come on after 20 seconds, 30 seconds, or 45 seconds. It depends on what your control board is set to.
There’s a little timer that decides when the blower motor should come on.

  1. Bad Control Board.

They can look differently on different furnaces but if you have a bad control board there’s a variety of different problems that can happen.
One of them is that it will not send power to a component. The board might not be sending power to the blower motor to turn it on and that’s why your furnace is overheating other times.
Sometimes, it not sending power to the igniter when it should be so the inducer motor will come on, the pressure switches will close but the igniter never starts to glow.
There’s also an instance where it’s not sending power to the inducer motor so your thermostat is set to heat but nothing happens.
We’ve also seen Control boards that turn on both the air conditioner and the furnace at the same time, of course, that’s a problem and most often that’s caused by a bad control board.
You need a meter to check the control boards to verify but if the control board is getting power into it but it’s not sending power out then that control board is bad. If you get lucky, sometimes the control board itself will blink an error code saying that the board is defective and needs to be replaced.
In that case you for sure need to replace that control board.
There’s a lot of problems that could be going in your furnace but this is the top 5 we listed as the most common. Check out more of our articles for more info and tips!

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