Gas Training - How To Test A Boiler Fan - Combi Boiler

how to test the fan on a condensing boiler my name is alan hart and in today's video we've got our friendly ideal engineer back and he's doing a a video on how to test a fan this video today is really really good it's an amazing video there's some sad news this is um this is the last video of our friendly ideal engineer unfortunately um i've learned so much from these videos that he's done for us have been amazing hopefully it may consider reconsider and come back at some point um but yeah let's show you this video one thing just to point out if you're going to work on any boiler please make sure you do all your electrical checks if you don't know what tb118 is search for it on youtube you'll find some of my videos that i've done with socket and c and it'll go through tb118 safety when you're working on a boiler also these videos are designed for gas engineers and for people trainees that are working with gas engineers and you should never ever diy with gas it's just not worth it so yeah let's have a look at this video this video is for gas safe registered and trainee gas engineers under supervision please comply with the current regulations at the time hello again youtube um today's video we are going to talk about the fan on the boiler specifically a condensing boiler fan the two types of fans on a boiler the first type is the non-condensing boiler the standard efficiency boiler which uh has an atmospheric burner the fan on that boiler is on the negative side of the heat exchanger which means it's after the heat exchanger it's pretty much an exhaust fan it removes the products of combustion from the heat exchanger it has a 240 volt supply it has a coil in the file which has a readable resistance you obviously need to know the resistance before measuring it to confirm whether it's uh it's good or not um dem fans are quite straightforward to test usually the problems is dry bearings due to the heat because obviously it's an exhaust fan and it's not very efficient so it pulls a bit of heat off the heat exchangers as well um so you know that's one type of fan but the type of fan i'm going to talk about today is the fan on a condensing boiler and i've been putting this video off um in the past because for me to explain um how you can repair this so find a fault with this fine i'm gonna need to explain exactly how it works because i believe to truly be able to repair something you need to know exactly how that part works for you know to carry out the repair correctly like i said the can the non-condensing boiler fan is on the negative side of the heat exchanger this fan is on the positive side of the heat exchanger which means it's before the heat exchanger and it's forced there where the other fan was an extractor it's it's drawing air up this is blowing air into the burner so it's a forced air burner it's a forced air fan so which blowing net positive pressure into that burner there however it's drawing negative pressure up this venturi and blowing positive pressure into the fan now i'm conscious of how long this is going to take so i may skip a few steps just because i'm conscious of the time i'm going to try to explain exactly how it works and how you can test it as you as i said before the [Music] uh non-condensable has one input it's a 240 volt input this has two it has a 240 volt supply on that one and on this one here there's a 5 volt dc supply this is known as the pwm the pulse width modulation signal this connection here is a permanent 240 volt supply so if you have power to the boiler um your fuse spurs on the boiler's powered up you'll have permanent 240 volts on this supply so i suggest if anybody wants to work on this fan you make sure the power switched off before you disconnect that lead otherwise you'll get a shock a nice surprise so whenever you're working on boilers obviously do your electrical isolations make sure you're working safely but that connection there is a 240 volt permanent supply so that's your first port of call if you have a fan issue make sure you've got your permanent 240 volt supply there if you don't you probably have a problem with the insta common supply um view spur pcb fuse um i'm not going to go too much and how you test that it's quite obvious you disconnect the leads and check for 240 volts ac obviously that's an ac connection however um there's a circuit board inside that fan and therefore when the fan's running it converts that 240 volts into 330 volts dc and when i said before the non-condensing boiler has a readable resistance through the coil this fan doesn't obviously because it's got a circuit board in it it has two inputs so there's no way you can test the resistance on this fan [Music] i'm going to talk about the pulse width modulation signal um in a little while but what i want to do first is give you a quick overview on how this fan works i'll be really i'll be as quick as i can like i said there's a lot of information i've been dreading doing this because i need to get the information in the right order for you to understand how it works but i'm just going to give you a quick rundown of how this fan works so again it's a forced air fan drawing negative air pressure into the venturi so first off the temperature sensors the thermistors the flow and return for misters are obviously sending information to the circuit board the circuit board has a pre-programmed algorithm in there and what that does so if we have a preset temperature on the board of 70 degrees the thermistors would say this is just a hypothetical um scenario the misters are reading 45 degrees on the flow which will then the algorithm in the pcb board would then say we need full fan speed it would send a pulse width modulation signal to the fan the fan would run on full fan speed it would draw negative air pressure up this venturi here and at the same time as it's drawing negative air pressure up this venturi at full speed it's also drawing gas through this injector up this pipe so it's a zero pressure governor so what happens is if there's zero negative air pressure at in this venturi drawing differentiate the zero gas pressure coming out of this gas valve so for pulling full full let's say 7000 rpm fan speed up here the air is great it would lift the gas valve seating up to its maximum drawing maximum gas through this injector the gas and air would then mix in the venturi and be blown into the burner where it's ignited once the temperature once the thermistors start to read a temperature getting up towards let's say 60 to 65 degrees the algorithm within the pcb board would then send a different pulse width modulation signal to the fan slowing the fan down drawing less gas less air pressure up this venturi which would pull less gas pressure through this gas valve so the seating of the gas valve would close which obviously then there would be less gas and air mixture less burner pressure at the burner that is just a quick hopefully a quick way to understand how this fan works like i said um it uses a pwm signal um i've drawn a little diagram for it would be easier for me to show you then to try to explain to you how this works so a pwm means pulse width modulation and that pulse width modulation is pretty much a digital signal from the circuit board to a dc motor it's more efficient than a normal sine wave an electrical sine wave looks more like a wave this is more efficient way to run the fan or any dc motor and what it does it pulses on and off quickly so that's where the pulse comes from and if you see here um this is the off it would pulse on off pulse on off pulse on off and pulls on and the greater the width of the pulse would be greater fan speed so our maximum fan speed of let's say 7000 rpm would have a longer width of the pulse so that's where the pulse width comes from a shorter pulse and off on off on off on the smaller the width of the pulse the smaller the the less power to the fan giving it a minimum fan speed so that's where the modulation comes from the modulation comes from the greater the pulse the greater the speed and then the fan can modulate between high and low fan speeds so minimum fan speed for instance would be 1000 rpm would be a small pulse maximum fan speed would be a longer pulse and in between them obviously depending on the pulse sent from the pcb board would determine what speed the fan rotates and how much air pressure it's drawing through the venturi and how much gas pressure it's drawing out of the gas valve mixing it and blowing it into the burner so that's been a 10 minute explanation on how the final works i'm going to set up my multimeter and i'm going to show you what tests you can carry out to actually diagnose a fault with the phone right okay i'm back i've disconnected the lead to the fan just so you can see the connections i'll show you it at the circuit board as well but as you can see there's three there's three wires there's a yellow a black and a pink the black is obviously the neutral or the ground the yellow is the feed and the pink is the input um it's a 5 volt supply the thing you've got to understand with this is because there's two inputs on the fan and the final circuit board there's a 240 volt input and a 5 volt input once you plug that five volt input to the fan you will not get the voltage reading off the fan uh off at the circuit board it's just because it goes through a circuit board and it's registering other other things um the first test i would do obviously disconnect the power pull that lead off and then find your connection on the circuit board which is this connection here and i don't know if you can see there's a black there's a pink yellow on a black a pink a yellow and a black so there's actually two pwm connections there and we have exactly the same principle on the pump so we have a 240 volt supply and a pwm signal to the pump so one of those connections is the pump and one of those connections is the fan now i know that the left-hand side connection is the fan and the right-hand side connection is the pump but if you didn't know that there's an easy way to um buzz out the wiring harness just to check um which one was which so what you would do you would disconnect the connection off the pcb board get your multimeter and set it to buzzer this is just a trace uh this is not to do a continuity um test i see a lot of people doing continuity with a brother you could probably do that with a switch but if you're testing something which has a resistance reading or a certain um well if you're testing the wiring harness you want to be doing the resistance of the harness on ohms but if you just want to check the harness you can set your multimeter to buzz and i'm just gonna try and put one of my connections in the yellow of the pwm we're on buzz and i'm going to try and connect my touching the yellow cable and as you can hear we've got a buzz if i disconnect that just proves that i'm on the right connection if i was on the other one on the other yellow we wouldn't get the buzz that's just the way to trace it to tracer cable you only trace a cable with a buzz if you are testing the continuity of the harness use arms anyway um a good thing to do would be to check the harness to make sure there is continuity at the harness to make sure there's no damage between this connection and the connection of the front otherwise obviously the fan isn't going to work but i'm conscious of the time what you would do is obviously put one of your test leads in the black put your other test lead in the black set it to arms looking for a reading of less than one ohm do that with the pink and do that with the yellow you're looking for less than one arm on your multimeter that's checking the harness once you've checked the harness plug the harness back into the circuit board leaving a little connection off so you can get your multimeter on these connections so you can test set our multimeter to ohms leave that connection off because we want to make sure we're getting five volts from the pcb board on the black and yellow um also on the black and pink when it's running however we get half the voltage but we will just want to make sure we're getting five volts first from the pcb board on the black and the yellow so we've checked we've set it on fire on voltage dc because this is a 5 volt dc motor and we're going to now test for five volts this is gonna be difficult today i'll uh put my phone down and i'll set it up okay this is very difficult to do with one hand we've got 4.9 volts dc i am testing between the black and the yellow on that pcb board right there so the yellow is the feed there we go again 4.9 volts dc and this time i'm on the black and pink that's your first check to make sure we're getting voltage from the fan to the from the pcb board to the fan and we are so what i'll do now i'll plug it in and i'll show you what to expect when it's running with the fan running i have got my multimeter set on dc um i've got a connection on the black and yellow i've put it on the fan only because i need my hands i wouldn't normally do this i would normally use the black and yellow on the pcb board to be testing this pwm signal this is the circuit board sending power to the fan as we speak um on the black and yellow we will have a voltage between 0.5 volts dc to about 1.8 volts dc depending on the pwm signal from the circuit board to the fan if i blow it down the potentiometer on the hot water you can hear the fan speed decreasing and you can see the voltage dropping if i again increase the potentiometer you can hear the fan speed increasing and the voltage increase and that's the pwm signal from the pcb to the fan so it's 0.5 roughly to about 1.8 volts dc depending on fan speed 0.5 will be minimum fan speed 1.8 would be maximum fan speed that's all black and yellow black and pink you would get a reading 2.5 volts dc [Music] to do with one hand and then don't do that connections on the circuit board yeah pull the connection 2.5 volts dc between black and pink and depending on fight speed black and yellow you'll have between 0.5 and 1.8 i'll just do it again to show you the fan's going out now i'll just increase the potentiometer again [Music] let the temperature drop on the thermistors there we go and then again [Music] now i appreciate that was a lot to take in um there was a lot of information to get across and i probably could have got that across better um but i'm not a trainer i'm just an engineer who knows a little bit about borders and that's why i originally said i would do these videos with alan because i wanted to give people she had a bit of knowledge and information about what i know and see if i could help a few people out and um over my videos i've actually had comments really nice comments most of the time um saying you know very informative video and i've had a couple of people actually message and say my videos have helped um with diagnosis of of thoughts on brothers i'm not a trainer um and now alan has got a trainer eyes on his channel now called roy he is a proper trainer um he does this stuff for limit living heat relays information to heating engineers like you and i so we can take it and digest it and use it i'm not um now roy's here i think it's probably time that i made my last video this is gonna be my last video because there's no point me making videos um trying to give you information and then him making the same video or vice versa him making one than me making one it's his job that's what he does he trains people there's no point me doing it now now alan's got one so i'd just like to say thank you for everybody for watching my videos thank you for the comments that you've left and i do hope that you've helped in some way um so yeah i'm going to leave it to roy i'm going to say goodbye and stay safe everybody thank you very much for that absolutely amazing video i know you said that you're not a trainer but this is probably one of the best videos that's been on this channel um so yeah thank you so much as i say i've learned so much from from you mr ideal man um please put some comments below let me know what you think to this video and thumbs up if possible and thank you thank you for watching

Channel: Allen Hart

Views: 71,301

Keywords: how to test a fan, how to test a fan with a, boiler repair, allen hart, alan hart, viva training academy, acs gas training, gas boiler troubleshooting, gas boiler maintenance

Id: 3dTlYRwDiEc

Length: 22min 58sec (1378 seconds)

Published: Fri Feb 26 2021