Gas Training - Sequence of operation gas boiler - Fault Finding

sequence of operation how does a boiler work my name is alan hart and today i'm at viva training academy and one of the questions that we've been asked quite a lot in the comments in the videos is if we could do a video on how a boiler works and and the sequence of operation and and what you need for it to work from the start so what what we're going to do today i've got roy here from viva training academy and roy's going to start the basics so he's going to talk to us about that you need your power and you need water etcetera and then it's going to go through the full sequence for you so hopefully this video should be of of interest to you if you can please put thumbs up on the video and also put some comments below let us know what type of videos you want and if some of these videos you'd like them to be in a different format again tell us how you'd like them um and we'll try and accommodate you best we can without further ado let's uh let's go over to roy this video is for gas safe registered and trainee gas engineers under supervision please comply with the current regulations at the time thanks al hi guys it's roy fuegler here at viva training category in halifax again and today we're going to go through sequence of operation we had a request from all the previous videos to go through sequence operation this is something i use for a good number of years i'm going to go through it on the board if you've got any questions about sequences any comments please put them down below and anything you want to know we're here to help you only have to ask in my book there's absolutely no such thing as a stupid question the only stupid thing is not asking that question because i'll tell you now for one person asks a question there will be a hundred people thinking of that question but not wanting to ask it to appear stupid so please please if you got any questions just ask so we're going to go over to the board and i'm going to go through a sequence operation and how to understand it even if you haven't got the manufacturer's sequence operation in front of you right so what i've done i've wrought down a generic sequence of operations some of these things will be in every boiler some of these things won't be some will some won't so we're going to start off we need to think about what boiler we're working on well i've gone for a good old favorite of mine the baxi 105 there's literally hundreds and thousands out there so from time to time up on the screen you'll see this wiring diagram popping up and i'm going to refer to it because what i need to do is use this and i've actually stood in front of a boiler and to determine what components are actually in the boiler and what sequence that they will operate so the first thing we're going to look at we're going to imagine that this boiler was stood in front of it we know that we've got gas in there we know we've got water in there so we're looking at it from electrical side so the first thing that we need is actually we need power without power that boilers useless and in my career i've been out to a number of boilers where they've not been turned on and the customers complained they've got no heat in the hot water dead easy fix making sure it's safe to turn the power on and we turn the power off so the next thing before we ask that boiler to do anything we want it to protect itself so there's three things it needs to protect itself from the first one is cross protection obviously in winter we don't want the boiler freezing up modern boilers have frost protection that's usually created um or looked after by the fourth mister the central heating thermistor so this particular boiler has a central heating thermistor so it will have frost protection low pressure protection we don't want the boiler firing up if there's not enough water in it so a battery 105 doesn't have a low pressure cut-off switch in there so we can actually remove that so we've no lower pressure protection on this particular boiler so we get rid of that because we don't need it all the heat protection now you'll probably notice that overheat protection is in there in several places different manufacturers bringing overheat protection at different times this particular boiler has got an overheat thermostat that's located just at the side of the thermistor on the floor pipe so it has got an overheat step i know for a fact where that kicks in and i'll come back to that it doesn't kick in at the start if it did and that kicked in we'd have power to the boiler and nothing else so again we can remove that so we now want this boiler to give us demand so either we've got demand for heating or demand for hot water so demand for central heating comes from our controls to our external controls and if we look on the sheet we've got a feed coming from a link which goes into a terminal and then we've got a built-in control so if we have the built-in control we can see on there we've got a couple of connections with black wires that's where that comes in so we will be testing there to see if we've got that external demand to prove that that boilers on there's a good little indicator on the backseat 105 if it has an external demand there's a little green light comes on with a radiator symbol so before we even need to get a multimeter out if we turn the clock up turn the thermostat i'll turn the programmable thermostat on and we get the little green light on there we know for a fact that that boiler knows it's got demand if it doesn't have the green light on what we can do is remove the wires out of there obviously by turning it off safe isolation referring to tb118 again always work safely we can put a little link in there the boiler comes out the factory with a link so we can just put a little inquiry and we're excluding external controls so if the boiler then fires up the heating we know we've got a control problem so that's what we'd look at for external controls hovering protection doesn't kick in there so i'm going to remove that so i'm getting rid of the overheat protection so hot water there's different types of floor switches this particular boiler has a pressure differential floss which that works with a diaphragm that moves in and out there's a little micro switch you turn the tap on there's a spindle comes out and it makes a micro switch so it's on here and it's indicated that there's a little micro switch so that's what we've got on there so we know that's what's been used for the hot water so the next thing is the diverter valve moves now on this particular boiler with it having that pressure differential it sits in heating mud and it moves for hot water so what we need to do is just put a little arrow to tell us that the diverter moves for hot water the next thing we're looking at the thermistors the temperature sensors some boilers have two thermistors on the central heating one on the floor one on the return some boilers don't have hot water thermistors this particular boiler has both a hot water and a central heating thermistor so we know that we've got both a central heating thermistor and a hot water thermistor so again we can look at those over heat protection no we don't kick in there so we can get rid of the ovary protection now we're talking about check the aps air pressure switch so air pressure switches that can sometimes be two wired or three wire this particular one when we look on there it's a three wire so what we've got is common and normally closed in this one's case the common is black and if i just put my specs on i can double check but i'm almost certain yeah the comma the normally closed is brown so we'll check between black and brown to make sure we've got a connection that's before the fan comes on if that connection isn't there the fan's not going to come off so we send power to the fan we need to know that fan comes on so if the fan then comes on we could check between common and normally open comet again is black normally open is blue so if we've got the fan come on the next thing we'd expect is the air pressure switch now this particular boiler at the same time it's doing the fan it will put power to the pump so it sends 240 volts down to the pump now do we need to prove the pump now again on the sheet we've got a little thing called um hydraulic differential switch some manufacturers like using big terms i'm a yorkshire man that's the pump proving switch if you looked at the brass diverter valve on here in front of the big brass section with the little micro switch on there's one at the back and when the pump comes on you can see the spin will come up and it makes that micro switch so yes we do prove the pump and this is where the ovary protection comes in because if it's overheated it will carry on the fan running and the pump running for a certain amount of time just to cool itself down so the next thing we look at the ignition sequence so power to the spark generator so again if we look at the sheet we've got the spark generator here and we've got a brown and blue connection and that's going on to a pin a plug called a1 and that's across three and five so we could check we've got 240 volts across three and five on a1 at the time we expect the spark generator to energize so the next thing is going down to the gas valve we've just done a video on gas valves so this one's got a modulation coil so the main coil the two solenoids again we're on a1 and we're on pins two and four brown and blue so we can check that out we've got 240 volts on brown and blue to the main gas valve solenoids so the next thing we'd expect is ignition we'd like to see a flame one sat flame which we're looking for rectification now some of the modern boilers the condensing boilers they'll rectify through the condensate trap so you'll see a leak coming from the rectification probe into the condensate trap and then maybe a little green and yellow lead going to earth the idea is if the condensate becomes blocked it goes up inside there it breaches across the two connections and it locks out so the boiler doesn't flood itself now this boiler doesn't have a condensate trap on there so basically we can get rid of that so the last bit is modulation how does it turn the gas up and down well this particular boil has a modulation coil so that's referred to as gv or gas valve three it doesn't work on fan speed your modern boilers your pre-mixed boilers the faster the fan runs the more gas comes through so this is basically a sequence of operation for this boiler so if we're stood in front of it it's not behaving correctly we can run through so we can turn the hot tap on so when we turn the hot tap on does the little micro switch come out and operate the floor switch if it does it'll then check the thermistors now it checks both thermistors on a hot water demand because the primary thermistor or the one in the central heating that's very clever it does three jobs it does as we mentioned earlier frost protection so if the car temperature drops below five degrees that will fire the boil up and get the car temperature up to about 30 degrees it monitors the con the temperature of the flow so depending on what setting the customer's got the floor temperature it will start to reduce the temperature as it gets up towards that set point the gas will modulate down and then the last thing it does it monitors for pre overheat before the overheat thermostat kicks in and the overheat thermostat on this particular boil is set at 105 degrees it starts to modulate so if we had a faulty floor thermistor what would happen is we'd have no heating but we'd also have no hot water if we have a faulty hot water thermistor it doesn't need it for the heating side so basically the heating would work but we could have a hot water problem now again thermistors can fail completely so it would flash up the error light or they could have drifted out of tolerance so we're not getting the right the accurate reading we're going to do a video in the future different thermistors testing them and the resistance readings that you're going to be looking for so that's that so coming on to the air pressure switch the air pressure switch measures through a venturi so eventually is a narrowing so what happens is as that air the fan's running it drags it through it creates a difference in pressure across that switch so it makes the switch operate so we need power going to the fan so if the fan doesn't run it could be that that air pressure switch will not get the connection between not common and normally clause so it doesn't know it's in that position if that air pressure switch has failed you could get the pump running uh sorry the pump could be running but the fan's not gonna run you've got a demand there but it's not running so it's going to check that before it brings the fallon because it needs to know that fans running so that it can get rid of the products of combustion infection out of clean fresh air once the fan's running it's looking for that switch to move down so it's looking for it to change across if it doesn't get that it won't go to ignition so we find the fans running the pulp's probably running but it's not going on again similarly we've got the pump proving switch if the pump's running but that little diaphragm is not lifting because the diaphragm could have stretched or we've got some dirt in the system while that pump's not running as fast as it could be we could have a situation where the pump runs but it doesn't go on to the next stage it won't go to ignition because it's not sensing that second microswitch that differential pressure switch it could be that so coming down onto the last bit power to the spark generator so we need to get that 240 volts as we've said across there and we need to get gv1 gv2 energized once we get the flame there we're looking for rectification a simple way to check that is if the flames lit but it's still sparking and it will only start for a matter of five or six seconds it's not rectifying one of the biggest issues on these particular boilers is reverse polarity so the live and neutral being crossed now if you guys are following what me and alan preach you should never get a problem with reverse polarity to this stage you should have checked that on your basic electric safety checks it's one of your fundamental checks before you start fault finding always do your electrical checks several times in my career or more than several times in fact if i hadn't have done the electrical checks i could have been going up a blind alley and changed components because i've done the electrical checks i've found out they've got reverse polarity one or two times it's been we've had some electrical work done and the sparky's got things crossed a few times when they've had smart meters so always do your electrical checks it can save you time in the long run you're not chasing your tail trying to find something that's not there the boiler water rectifier some of the newer boilers will actually work on reverse polarity the manufacturers have designed them to work safely on reverse polarities to cut out nuisance visits so once we've know that it's rectifying we're looking at modulation so if the gas doesn't jump up it could be we've not got the voltage going to the modulation coil or the modulation call's got the voltage but it's not energizing because that coil's failed so again that's just a sequence of operation that can be adapted for any boiler so long as you've got a wiring diagram or you're stood in front of the boiler you know what the components do that's a very simple way of writing it down some of the manufacturers now actually give you in their instructions and the sequence of operation and if you follow the fault finding guides on the back that is like a sequence of operation does this happen yes no and then you're following him through but i've used this for a long long time and i find it always works whatever the boiler is if you write something like this down and just cross out the ones that aren't used then it's a really good sequence operation guide if you've got any comments any questions any queries as i said at the beginning please ask us put down your comment like thanks very much until next time thank you bye thank you very much for that right and once again thank you to viva training academy if you've got any questions as always put comments below and we'll try and answer them the best we can and if you've got any suggestions for any other videos again put some comments below if you can put thumbs up a bit that'd be good and also if you want to subscribe yeah all that good stuff and thanks for watching

Channel: Allen Hart

Views: 66,572

Keywords: how does a combi boiler work, online boiler training course, combi boiler, boiler repair training, gas training, viva training academy, viva gas training, viva training halifax, gas boiler, acs gas training, gas safe, gas training videos, gas training tutorials, gas training course, gas training centre, gas engineer training, gas training tutorial, gas course, gas valve solenoid test, Sequence of operation gas boiler, Sequence of operation

Id: pL3GbvIHueE

Length: 17min 56sec (1076 seconds)

Published: Tue Apr 06 2021