Hey guys this is AC Service Tech and today what
we're going over are the top ten reasons why the pilot light goes out so this applies to furnaces,
water heaters, ranges, all kinds of appliances This also applies to appliances that you're trying to
light and it's just not staying lit so say you hold your pilot button down for a minute or so or
maybe even two minutes and you let it go and the pilot just goes out in that case I only held this
button down for five seconds but in cases where you are holding it down for two minutes that flame
should stay lit so you know what's happening this is your gas valve and right down here you
see this this little plunger right here that's attached to this this little solenoid right here
so you have your thermocouple rod heats up and it sends millivolts to this solenoid right here this
part and when we press this down we're actually pressing the plunger down and the millivolts
are supposed to keep this down like that so when there's no heat here there's no millivolts
and therefore this comes back up and shuts the gas off to the pilot tube Before we get into the
top ten reasons I just want to do one last test and this is a thermocouple tester and what this
does is it gives you a contact for the inner wire of the thermocouple so the thermocouple is made up
of two wires you see right here there's an inner wire and an outer wire and you want to be able
to read the voltage with a clamp on each of those wires the issue is you can't measure it when it's
connected into the solenoid so that's why we have this right in line between the thermocouple and
the solenoid in order to put our alligator clamp right here and one right here and now we're going
to go ahead and test it out now this was a little warm right here so we have 0.2 millivolts already
our multimeter is set on DC millivolts I'm gonna go ahead and hold this down and we're gonna
put a flame to the thermocouple we're gonna see when this solenoid starts to stick right there
so it looks like it started to stick and hold at about 2.5 millivolts so let's just see when
this pops back up again Even though this is a 30 millivolt thermocouple you see that the solenoid in
this case only needs around 2.5 millivolts or so and there you see at about 1.6 it's letting
go so there's not a lot of heat that's needed in order to hold this solenoid in position to allow
the gas to come into the pilot tube on the gas valve This is problem number 1 a bad thermocouple
rod so you see we have the end of the thermocouple detached from the combination gas valve and
we have our multimeter set on DC millivolts we have our alligator clamp on the end of the
wire which is actually connected to the inner wire and we have the other clamp connected to
the outer wire so now we're going to go ahead and light the pilot and you see that the flame is
enveloping the thermocouple rod but we don't read any millivolts so that means that the thermocouple
rod is bad now you could hold that pilot down longer than I did but you see that we didn't even
read point 0.1 or 0.2 millivolts you could try again just making sure that your alligator clamps are
making good contact but that just shows that the thermocouple was actually bad in this case This is
problem number 2 a dirty thermocouple rod So this one has a thick layer of carbon on the outside
and that could act like an insulator and it's not providing the correct amount of heat to the
thermocouple inside of the outer rod and so you want to go ahead and clean that off so we would
use unsoaked steel wool in order to clean that off and you want to make sure that you don't get
any pieces of the steel wool down inside the the pilot tube here because you don't want that to
accidentally clog off so if you can pull that out in order to clean it that's best or you can
just blow it out afterwards so you see that we can typically just pull them out and then you can
clean them outside of that just to make sure that you don't get any dust in there but regardless
you go ahead and you just take this steel wool and you just go ahead and and clean it off you
make sure that you don't use sandpaper or anything else that will leave other residue so we're just
using metal on this metal and that cleaned it off so now you can go ahead and try again and see if
the the thermocouple will now send the correct millivolts in order to hold down the solenoid
valve Problem number 3 the thermocouple rod may not be high enough or in the right position
to be enveloped by the flame so maybe the brackets worked or maybe the thermocouple rod has slid
down maybe the little tension bracket is not holding it in place correctly but let's just go
ahead and light this and you see that the rod is not in the flame so it's not going to heat up and
it's not going to send the DC millivolt signal to the gas valve in order for the pilot to stay lit
so that could be the problem Problem number 4 is where the thermocouple connects into the
bottom of the gas valve at where if it's in the top or side basically if you have a loose
connection right there that's not gonna allow the millivolts that are generated from the heat
applied to the thermocouple into the solenoid so let's go ahead and light our pilot and we see that
the flame is enveloping the thermocouple rod we're gonna need to hold the pilot button down until
we generate enough electricity that the solenoids gonna be held in place I'm gonna go ahead and
let go of the button now we'll see if we've Apparently we've generated enough electricity and now
we see that our pilot is continuing to have its flame there let's go ahead and just loosen this
just a little bit and you see that we lost our flame so you could have just a bad connection
right here Problem number 5 could be a bad solenoid so in this case we have our tester in
place in between our thermocouple and where it connects into the solenoid at and we're gonna go
ahead and light our pilot and we're gonna read our DC millivolts you see our thermocouple is still a
little warm from the last time it was just on so it's reading 0.5 millivolts so now I'm going
to go ahead and light the flame and you see our DC millivolts are rising rapidly and from our last
test we know that 1.5 to 2.5 DC millivolts were enough to end up holding the solenoid in place so now
I'm going to go ahead and let go of the pilot button and lets see if the flame stays there And it doesn't so in this case a solenoid is actually bad because we have enough voltage to hold the
solenoid open, make sure to hold the pilot button down for a longer period of time just in case a
solenoid takes a higher DC millivolt signal in order for it to stay open Problem number 6 is
low gas pressure or low pilot filling pressure So let's go ahead and light it and you see that
we have just a tiny little flame and it's really not even touching the thermocouple rod and this
would definitely be an issue Now you can adjust your pilot flame if you have the correct inlet
gas pressure coming in there's typically a screw for an adjustment on that You know on this one
right here you just take this screw out And then you can get to the adjuster screw on the inside
and adjust the pilot flame accordingly Another problem that you could have is a kinked or closed
off pilot tube so if you're letting your flame and the flame is just very small or maybe you're not
even ignited at all and you've adjusted the pilot screw you know it's possible that there's a clog
right in here or the the tube is kinked So in that case what you could do is you could take your tube
off of the pilot termination here and you could have either a clog in this tube or a kink you know
you want to make sure that you take both sides off you could use compressed air make sure that you're
blowing through there and in reference to this there could be a little clog in the orifice make
sure to not use a needle because you don't want to enlarge the hole but basically I don't know if
you can see this or not but let's see if you can if you can visually get this but there's a tiny
tiny little hole in there and sometimes you can actually just take that out and clean it up and
then put it back in again or you you could replace the entire assembly Problem number 8
your manual gas valve outside of the appliance could be in the off position so this is in the on
position with basically the the handle facing the gas pipe direction so when it's perpendicular to
the direction that's when the gas is off So you could be trying to light the gas but it's just
not lighting you could just have the gas valve off You can also check the natural gas meter
outside maybe that's shut off or the propane tank is out of propane Problem number 9 to
be a bent or worked pilot termination head so you see how this is kind of bent over as it is
right here and that's the flame envelops the thermocouple rod and so what happens is over time
this may be overheated and may be warped and bent upwards and now the flame is going upwards instead
of enveloping around this thermocouple rod so in that case you may not want to just bend that you
may want to go ahead and replace the pilot head just to make sure that the flame is in the correct
position Problem number 10 is wind blowing at the pilot flame That's because you're not getting
a continuous heat source on the thermocouple that could be due to the exhaust location or
pressurization inside the building that could be due to a multitude of different reasons The big thing is if there is a problem maybe with the the DC millivolt signal of the thermocouple
sometimes wind is is blamed but it's actually the thermocouples going bad so it could be a
combination of a couple things so you just I mean these are cheap enough the thermocouple is cheap
enough to just go ahead and replace that part but you just want to make sure that you have a nice
flame enveloping the thermocouple rod and under normal operating conditions you don't see the
flame blowing around a lot just due to some type of wind source If you're looking for any of the
tools using this video I have them linked down in the description below and if you're looking for
any other gas furnace troubleshooting videos I have them linked down there as well If you want to
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we'll see you next time at AC Service Tech Channel
