Furnace Not Blowing Hot Air - Easy Fix

hey guys Jay here with word of advice TV

so today after lunch my wife calls me up

at about one o'clock and tells me I just

came home and it's 61 degrees in the

house I'm thinking shoot I'm only going

to come home at like 6 o'clock it's

gonna get even colder by then so I tell

her okay just go down to the furnace and

tell me what it's doing and she says

there's no flames that glow thing is not

glowing nothing's really working up on

top but the fan is running so I tell her

all right can you look in the sight

glass on the bottom door and tell me if

you see anything that she says yes I do

see a light inside the sight glass I

tell her okay that's great now if you

could just count how many times as

blinking and let me know and she was

counting it you know one two three four

pause one two three four so I was

blinking four times so on my control

board I have a diagnostic chart it's

either gonna be on your board or in the

back of your furnace door in fact let's

just take them off usually on most

furnaces the diagnostic chart that

explains your error culture fault codes

will be somewhere on the back of your

furnace door and mine all I have is a

schematic as you can see but on most

furnaces that diagnostic chart will be

on the inside of the furnace door in my

case most furnaces don't have it like

this but on mine my diagnostic chart is

right on the control board itself and on

my board it says here that four flashes

means that my thermal protection device

is open

and just so you know I'm different

furnaces that will be called different

things for example your board might say

or your diagnostic chart might say that

your upper limit is open or you have a

limit lockout or it will say high limit

open something to do with the limit or

in my case it said thermal device but it

was talking about the high limit which

is right here on most furnaces it will

look like this it's a black square like

that and that is your thermal device or

your high limit switch so if your

furnace is ever overheating this switch

right here shuts down the furnace and on

some furnaces instead of a rectangle

like this it'll be either black or brown

sometimes it'll be a bi-metal switch and

it'll be just like a round little thing

I'll add a picture so you can see what

that looks like so it's blinking four

times right which means my high limit is

open and I'm thinking okay maybe if she

resets the power and it's perhaps it's

in a lockout if it overheats so many

times the furnace will go into a lockout

where it just sits there for three to

five hours and just does absolutely

nothing so I tell my wife all right shut

down the furnace power switch leave it

off for like five seconds and turn it

back on does the furnace do anything

different so she did that turns the

power back on and still nothing you know

nothing up here works but the fan turns

on and that control board is still

blinking four blinks

so what happened in my case is my

furnace was overheating for probably

like a week or so by now I was actually

forgetful and I forgot to change my

filter for probably like two or three

months I usually change it every month

and a half and my filter it doesn't look

that dirty but I guess we've been

burning some candles lately and the

residue from the candles for some reason

just plugs these filters up with this

waxy feeling stuff I guess it's

literally just the wax from the candles

but that really plugs up filter so if

you burn a lot of candles make sure you

replace their filters every month but

anyways I forgot about my filter for

probably like three months so my furnace

was overheating and the way that switch

works it's two different kinds of metals

and they're made out of different

materials so if for some reason your

furnace is getting too hot one of those

metals will

warp and separate from the other one and

as you can see right here the switch

only has two wires so you know you're 24

volts will go into one side and that

switch is normally closed which means

normally operating furnace this switch

should always be closed power will go in

one side and then come right back out

the other side but if it's overheated

and that bi-metal opened up then that

switch is going to be open and not allow

the circuit to go through and if this

limit switch is open then your igniter

will not glow and your gas valve will

not open but anyway back to my story so

my wife told me is blinking four times

she tried resetting it nothing's working

so being the good technician that I am I

tell her okay no problem

take out the doors and I'll walk you

through it I'll tell you what to do

you'll get it fixed in no time

unfortunately my wife was not as

enthusiastic about digging into the

furnace as I was so she told me no

thanks I'll just put on an extra pair of

socks and wait for you to come home so

of course you know later on that's 6:00

6:30 I come home and within a couple of

minutes I got my furnace back up and

running and in a little bit I will tell

you how I did that but before I do that

just real quickly for those of you who

are interested I'll just show you how to

check that switch with a meter if you

wanted to there's two ways you can check

it one way is to check voltage which is

what I prefer I usually prefer to check

voltages more than resistance but you

can also check the resistance or a

continuity since it's a switch so if you

set your meter to let's get my

flashlight so you can actually see it if

you set your meter to continuity which

is that right there that symbol and

mines magnetic so I'll just flip it

right on here somewhere or maybe even to

the inducer motor and then and then just

unplug the wires both of the wires going

to your high limit switch so you just

have the terminals and with your meter

set to continuity put both leads on both

terminals like this

as you can see my meter is beeping which

means this switch does have continuity

now if this switch was oh L like you see

rate on my meter like that that means

that switch is open or you can just

check the resistance that Omega symbol

or the ohm symbol almost the same thing

put your leads on both terminals except

when you're checking resistance there

won't be any beeping as you can see I

have about 1.8 around 2 ohms of

resistance which is normal for this

switch so I know my switch is closed and

like I said previously it's a normally

closed switch so you should have some

kind of resistance or continuity between

the two terminals so that's how you

check resistance and continuity but the

way I prefer to do it is to check

voltage so you do need to have the power

on for this so turn the power on my

thermostat upstairs is calling for Heat

I had my power switch off the whole time

so the burners aren't on while I'm

talking so there it goes my inducer

motor my igniter is gonna start to glow

my pressure switch is closed so by this

time my high limit should have 24 volts

going through it so if I go from one end

to the other if you look at my meter as

you can see I have zero volts and for

those of you that don't know a switch is

literally just that it's just a switch

almost like a piece of wire so if the

switch is closed you won't have any

voltage drop so no voltage it will be

zero but if that switch is open you will

have around 27 volts so for example if I

keep one lead on one terminal and put

the other lead to ground and what I mean

by that is just any screw that's

attached to the furnace cabinet

so for example I'll just go right to the

sky limits true as you can see I have 26

point 4 volts coming in and if I go to

the other terminal

like that I have 26.4 volts coming out

that way I know that the switch is

closed so once again when checking

voltage you just put your leads on both

terminals and if the switch is closed

you'll have zero volts if it's open you

will have twenty six volts so that's how

you check it with the meter now on to

the part of how I actually fixed it

fixing this is actually pretty easy so

basically that switch is stuck open a

lot of times if you just smack it a few

times that'll be enough to cause those

two metals to come back together so in

my case I just took a screwdriver and it

was enough to just whack the limit just

on the faceplate right here just a

couple whacks or good whacks

I just want pam pam pam pam pam i reset

my furnace turned it back on and

everything lit right back up so it was a

really quick fix now sometimes if it's

really stuck open you have to take that

switch out and I'll just show you quick

so you know what it looks like inside

sometimes you have to take it out and

give it a couple of good whacks with the

high-limit out and I have had a couple

times where no matter how hard you hit

it the thing does not close back up in

that case you just have to replace the

high limit so anyways I took out the two

5/16 screws and let's take my switch out

this is what mine looks like it has

usually it'll have some insulation on

the inside and then here's that bi-metal

part that I was talking about you can't

really see the two metals inside they're

all internal but basically here's the

sensor which is usually facing downwards

and on most high limits this will just

be two prongs mine has a plastic casing

it's just an older furnace not a lot of

furnaces will have this plastic casing

and some of them there's different

lengths some of them are a lot longer

maybe like up to here but yeah this is

the high limit it's nothing too


so if hitting it on the face does not

close it up for you you can try taking

it out and just just

against your furnace or against the

floor not too hard just firmly - trying

to close that back up and almost all the

time that is enough to close that thing

back up and your furnace will start back

up well and that's how you manually

reset that high limit switch in my case

it was a dirty filter and most of the

time that's what it is your filter is

just dirty but there is a lot of other

things that can cause your furnace to

overheat I won't go into that in this

video but I am planning and making a

video right after this one on ten

reasons why your furnace can overheat so

if your problem is not a filter then you

can go ahead and check that video out

for more ideas of why your furnace keeps

overheating and just one more thing I

want to mention a lot of times people

they read their code and it says high

limit open the first thing they do is

replace that limit switch just so you

know it's very rare that that limit

switch fails doesn't happen a lot at all

usually it's just doing its job and it's

opening up because the furnace is

overheating so you have to figure out

why it's overheating and get that fixed

or cleaned up and that is all I had for

this video today I hope you found this

information useful thank you so much for

watching this video don't forget to mash

that like button on the way out and

we'll see you next time and for those of

you that are still here I want to show

you some brownies that a customer gave

me he tells me hey you want some

brownies they're high in fiber and low

in calories and low in fat they're very

great you want some and I say yeah sure

I'll have some so he brings him out to

me and he hands me these brownies