Gas Training - How Thermistors Work And How To Test - Viva Training Academy

gas training how for mrs work and how to test my name's alan hart and in today's video i'm back at viva trading academy and we've got roy and roy's going to go through for mrs how to test them i've also put roy in the naughty corner today so that's a little bit of fun later on in the video uh yeah so ride's gonna go through for misters we'll go through how to test them how to drop them on floor as well um and why you are famisters in boilers so yeah let's uh go over to riley this video is for gas safe registered and trainee gas engineers under supervision please comply with the current regulations at the time hi guys it's roy fueber here at the vivo training academy auburn halifax again and today we're gonna have a look at uh thermistors talk about different types of thermistors what thermistors are what they do we're gonna go into the workshop and show you how to test if they missed on a live boiler uh i'm also playing with my new toy i've got a new fluke multimeter here and it's got an app on it which is actually linked onto my phone so now when i'm doing uh videos and we're looking at resistances voltages whatever i need for my multimeter i don't need to keep screwing my neck around looking unprofessional i can have a quick glance down at me firm and see what we're doing so what i'm going to do is just push the record button on here so it's recording what i'm doing i've also got my kid and 458 analyzer in the reason for that is just to check the temperature because thermistors are temperature sensors so i just wanted to get myself a base temperature in here and the temperature in here is about 21.7 degrees it's nice and warm because i know um alan don't like it too cold when it comes in here so what's a thermistor it's a temperature sensor now different manufacturers will call them different things i've heard them called temperature sensors floor sensors thermistors ntc sensors well ntc means negative temperature coefficient and that's how these particular thermistors operate what that means is as the temperature rises the resistance goes down and so that's how that works the higher the temperature on these particular ones the lower the resistance we did in our industry used to use ptc's positive temperature um coefficient thermistors which basically as the temperature went up the resistance went up so they did that so what i'm going to do is just have a little look at these different thermistors i've got all sorts of different ones in here um i have a little brass one there i can't even remember what that one come out i think it's out of an old worcester it's a few years old it's a brand new thermistor but it's never been fitted i've got a clip on one there that's used on a baxi system boiler uh another clip on one i've got a dry pocket one out of a romeo and that's out of a worcester that's a floor thermistor a little brass thermistor there which um lots and lots of manufacturers have used that one bax has used it the carers used it lots and lots of used it so all sorts of different thermistors in here now with the thermistor what you all have is a base reading and what we're going to do throughout the video we'll put charts up so you can you can get an idea of what we're talking about so the most common base reading is 10 000 ohms at 25 degrees so a lot of thermistor manufacturers will use that so what that means is if i measured the temperature and it was 25 degrees i would get 10 000 ohms now this particular thermistor i know is a 10 000 ohm at 25 degrees as we've already said it's about degrees in here so i'm just going to go across it now what i've done when i take all wiring harnesses out i'll take all boilers out i'll strip the harnesses out and i make myself little test pieces just so that it's easier to get in because some of these thrifters like this particular one the pins are quite close together getting your probes in off your multimeter can be quite awkward if you've got a little test piece you can just plop it in and then you've got a little chalky block on the end of it and all i'm going to do is go across that terminal block there and just have a quick look and the reading there i'm getting 10.3637 it's still moving a little bit so 10.42 on that one uh as i'm reading it now so it's settling around but if we said around about 10 and a half thousand ohms cost the k means thousand so that's that one so that's a 10 025 degrees so it's not too far away there is a tolerance on feminist there's most manufacturers say a 10 so as long as we're in that tolerance so i've got another one on here which is a 10 000 so this is a little and thermistor that goes into a pocket i think that came off a back boiler actually an old boxy bermuda so i'm going to test that one and the reason i'm getting on there that one's 12 000 uh 120 so 12.1 k so that's what i'm getting on that one um so this little fellas out of the wooster quite common to a lot of you guys i know allen's fitted quite a few busters in the past weeks quite familiar with this one now this one worcester are quite specific on theirs they give an actual figure now i've got to cheat i've wrote it down 11 981 ohms at 25 degrees which is quite specific and on their chart they've got all the figures so if we are looking at them we always refer to the charts that are in the manufacturing instructions or on their websites on off their technical help lines so i'm just going to connect onto this one so with it having a slightly different base reading it's going to have a slightly higher reading at the temperature we're at which again is 20.66 degrees so this one's sitting there at 14.24 k so 14 240 ohms so that tells me it's a good reading so again this one this is out of a remainer it's also out of the latest baxi uh range of heat only boilers it sits in a dry pocket i'll come back to that in a minute or two so it just screws on there and again this is a 12 000 at 25 degrees so again we're just going to check that one so there we go 14.3 so it's not much different to what the the worst one was so it's it's within that tolerance of the 12 000 thermistor now this particular one this one is actually a flu thermistor so when we're looking at thermistors we've got different uses for thermistors hot water sensor floor sensor return sensor flue sensor anywhere where we need to measure an accurate temperature a thermistor is used so if we're thinking about the hot water thermistor the temperature that that's going to come across if we think about the cold water coming in in winter it could be coming in as low as 5 degrees we will ideally want it to get up to 60 we know it's probably not going to achieve that because most manufacturers talk about the 35 degree rise from cold so if we're coming in at let's say 20 degrees in summer we're only going to get that to maybe 55 degrees and that's going to be pretty warm typically in this country we're looking at mainly the cold water somewhere around about 10 to between 10 and 15 degrees so with that we're looking at 45.50 and so that's the temperature range that we'd be looking at somewhere between maybe five degrees up to 60 70 degrees on the central heating side we don't want it going any lower than maybe five degrees and a lot of boilers modern boilers they have frost protection which if the thermistor on the floor pipe or the return pipe sensors a resistance reading equivalent to five degrees it will trigger the boiler to come on on frost protection boiler maximum temperature we normally say for eighty so we're looking at somewhere between five and eighty so most manufacturers will use a thermistor which is between sort of zero degrees up to a hundred degrees because it covers that band they'll also use that one for the hot water so you'll find that the really typically the same sort of thermistor they're using for both hot water and heating all the same bandwidth now when it comes to fluid fluid is a different kettle of fish flowing can be quite high so this particular thermistor again it's out of a baxi or a gionee style heat exchanger now this one is designed that if the resistance reading gives the circuit board a temperature which is 150 degrees it will basically flag an error code up because it doesn't want it to get too hot and damage that heat exchanger that heat exchange is from a condensing boiler so really it shouldn't be getting much above 60 65 degrees anyway so this uses a higher resistance reading we're looking on this one it's a 20 000 ohm at 25 degrees so i'm just going to test this one for you so we can see what it's doing so we're on there and i've got a reading of 22.8 k 22 22.86 it's just there in a little bit as the temperature changes so that's just a little bit about them so just to give you an idea of how quickly these things react i've got another 10 000 one here so i'm just going to stick my probes on there and i'm also going to get hold of it and you'll see how quickly it changed so at the moment we're getting just over 12.3 k so if i grab hold of it as we can see now my body heat is causing that temperature to go down so obviously the resistance is going down so we're getting down to 10.5 10.4 10.3 so it's coming down so they act very very quickly so a way of testing a thermistor out in the field is actually if it's in a dry pocket take it out get your multimeter across it and touch it which is fine if it's in a wet pocket you don't really want to be taking it out because you've got to drain it you can grab all of the pipe where that thermistor is located providing the boilers not too hot and typically we're going out to look at boilers because they're not functioning so the flown return pipes are quite cool so we can look at that thermistors can fail they can go open circuit as we've talked about in the past which means there's no connection across there so the circuit board doesn't pick a reading up and you'll usually get an error code coming up the other one is they can go to a too lower resistance where they're starting to get what's called a short circuit on there and if the resistance is too low if it's outside the tolerance band that the manufacturers are looking for again it's going to flag an error code up so then it's going to point you in the direction of that thermistor the other one that they can do and i've talked about on a previous video is what we call drifting where we're getting a reading but it's not the accurate reading it's not within the 10 to 20 that most manufacturers say that their thermistors are so that's how we can test them on a bench and we can also pop a little test piece in there and check them out in the field it's slightly different so what we're going to do now we're going to go into the workshop down here at viva and i'm going to show you how to test one on a live boiler i'm really sorry guys i've been in the naughty corner alan put me in the naughty corner we've just reviewed to edit the video and what he realized i've done i've made a mistake what i said was the temperature going up and what i sort of said is the temperature goes down on a thermistor resistance grows up temperature down my body heat was taking the temperature up so the resistance was coming down so i apologize i've been in the naughty corner so we're going to crack on so we've got a green star system boiler here we've had it on all morning it's been warming the classroom up where we've been in so we've got 82 degrees on the screen there so i'm gonna turn the boiler off isolating i'm going to show you how to test that thermistor so we're going to carry out safe isolation we've gone through all that in the past so we'll probably cut at some point just so you know see me doing all that again so here we go we've done the isolation now so we we can remember we've got 82 degrees in there so that's quite a high temperature so we'll be looking at a low resistance reading now one of the things when we're testing on on live boilers if we're testing components now this one all i need to do just drop the front one screw two little catches and i'm into the wiring where all the components are the right hand side tends to be the lower wiring uh low voltage should i say and the left hand side is high high voltage so i've looked on the set of instructions and it's basically telling me my flow thermistor which is number 13 that it's on two red wires and i trace it round and it comes onto this long block here and it's coming in on terminals six and seven now if i was to do a direct connection onto six and seven i'm probably going to pick a reading up but what might happen is i may pick up a back feed off the circuit board so i'm picking up not only the mr reading but the circuit board so i'll just connect onto those two with it still on there and on this particular buster board there are some little indents where you can get the probes of your multimeter in so you can get them into this i'm just going to go on to the two little connections there and what i can see i'm getting 1.458k so 1400k which isn't too far off what i'd be expecting on the chart um because i've looked on the chat and it's not too far away so i might think that's a good reading but just to make sure i get the perfect reading i've just disconnected it and this is where you've got to be careful with your probes that you're making sure that you don't push them in too far and start damaging things so i'm just going in there and i'm just going across those two connections and i just need to get in a little bit better with with that one just to make sure we're actually on that terminal so i'm in there now and i'm getting 1.69 so just shy of 1.7 000 ohms so you can see there's a difference on there so it could make make a bit of a difference if we're reading so when you're testing components electrically testing the main things are isolate your boiler safe isolation tb118 is what you need to refer to but when you're testing something always remove it from the circuit board and either test at the wiring going up to the components or as you've seen what i tend to use um in a little test pieces because it's easier sometimes to get them in there and plug them in and you're not damaging the little connections on the uh the connector that goes onto your pcb because you don't want to start damaging wiring harnesses you've got to be fairly gentle when you're putting your probes in not not jamming them in there and damaging things so that's been a little bit about testing thermistors i've been in the naughty corner which hurts a long time since i was but i'll hold my hand up i do make mistakes so i do apologize i hope you've enjoyed the video if you have please comment down below and put a like on there that's great give us some feedback again good bad or indifferent we're quite happy if we've made any mistakes let us know about it we really appreciate you coming back to us so hopefully that's been of use to you for you guys out there understanding what thermistors do why we have them it's quite an important little piece we think about the circuit board being quite expensive but the circuit board is only the brain and your brain can't function without your senses if i can't see what i'm doing i'm hopeless and that's what the thermistor is doing it's giving that brain that circuit board some information which is determining how hot it is how cool it is so whether it comes on or goes off so that's just a little bit about thermistor so thanks very much from me roy fuegler over at viva until next time bye-bye thank you once again to roy and thank you to viva training academy for all the help and support if you've got any questions please put them in the comments below always remember if you're going to work on a gas boiler you must be gas self-registered and you must do all your safety checks tb118 is very important if you're going to do any testing in boilers so please check out the video that we did we i did a video with socket and c and we did a video on on tb118 so if you search for tb118 and you'll find that video on sapphire isolation and working on boilers um yeah if you've got any questions as i said please put me in comments below and thanks once again to everybody who watches and supports the channel um yeah thank you

Channel: Allen Hart

Views: 6,173

Keywords: gas training, gas training centre, viva training academy, gas boiler, fault finding, how to test, boiler breakdown training, boiler breakdown course, boiler breakdowns reviews, gas safe training, gas training tutorials, gas engineer training, gas training tutorial, acs gas training, gas training course, gas training uk

Id: IlMUbXUt5Mw

Length: 17min 44sec (1064 seconds)

Published: Sat May 01 2021