TOP 10 Reasons Why the Gas Pilot Light Goes Out & Won’t Stay Lit!

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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you want to see another HVAC our training video click right here   Hope you enjoyed yourself and 
we'll see you next time at AC Service Tech Channel


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