BAXI COMBI INSTANT 105E Won't light

[diamondgas]

Chillyisons, This is where you need to have the gas certs behind you. You really need to know if there's any gas pressure at the burner. If you're getting power to the valve and a spark at the burner you'd be expecting a flame!! Thing that's throwing me is the 30&40 light flashing together. I've had this once before on a board less than 12 months old & I tore my hair out coz I'd replaced the board prior and ruled it out as faulty! Turned out the new board was faulty! If you're getting 240v pin 2&4 whilst the spark is occurring then I'd be edging toward the gas valve........ Best guess ..

 

[Billy Bob Bob]

water and pcbs dont mix,to the op if you could answer did the fault occur after the water carrying parts were replaced? my moneys still on a soggy pcb

 

[diamondgas]

water and pcbs dont mix,to the op if you could answer did the fault occur after the water carrying parts were replaced? my moneys still on a soggy pcb

I know what you're saying gas man. that's why I'd want to know if there's gas at the burner and at what pressure.

 

[chillyisons]

Right then. Gas cert man came out and after a very quick check said pcb and when I quized him on what makes you say that the reply was the following

when the boiler is swithched on the fan spins and pump starts boiler sparks. Fault lights come on and total silence... no spark no fan and no pump. Hold the selector switch to the reset position and while being held in reset the spark starts again but nothing else which I have been told it shouldnt do in the reset position. From what I understand it should do nothing while being held in reset position.

Mr gasman... yes it stoped working after water carrying parts were changed. The board was dried to within an inch of its life but still wouldnt work and it has since then been total cleaned (top and bottom of pcb) with a highly solvent based electronic cleaner and allowed to dry again and still wouldnt work. It has now been 4 full days since the pcb had its unwated water bath so im of the opinion thats its now fully dry but somthing shorted and caused damage at the moment of water contact. mabey???

Mr diamondgas... As for the 240v at a1 pin 2 and 4 for the gas it is only for a fraction of a second. The sequence is

1. Fan starts
2. pump and spark start at the same time
3. 240v appears at a1 pin 2 and 4 for not even half a second. It hardly even has a chance to show the 240v reading on the multi meter before disapearing its that fast so doesnt even give the boiler a chance to try and light before failing it and displaying the 30/40 degree lights flashing and everything shuts down.

The upshot of this is the gas guy has ordered the pcb (Honeywell) £100 + vat but due to someones wedding and bank holidays it will be tuesday before it makes an appearance🙁.

I will get him to check burner pressure when he comes on tuesday but I wish Id remembered the burner pressure and had it checked at the time but hay ho.

Although im clearly no expert on boilers by any stretch of the imagination I would have thought the pcb would have given the burner more than one spark which is all it gets between 240v appearing and then droping to 0v at the gas block to allow the gas/air mix a short (1-2 seconds?) of gas valve open and a few clicks of the spark before deciding that its not actually going to light? I know its got to cut the gas at some point so it doesnt build up to the point where if it finaly lights it will blows its self into orbit but less than half a second to me seems too short. Thats just my thought and as i said I KNOW NOTHING!!🙂

 

[fixter1]

all been well you did say it was getting 240v nothing about it droping to 0v.... and only one spark so if you where not getting voltage fault would be on the pcb at least you will have you heating back after the weekend y could he not get one today???

 

[chillyisons]

all been well you did say it was getting 240v nothing about it droping to 0v.... and only one spark so if you where not getting voltage fault would be on the pcb at least you will have you heating back after the weekend y could he not get one today???

The end of post #1 when the fan and pump initialy spin the pcb shows 240v at its various sockets which is cut as soon at the fault lights come on

and post #20 240v at 2 and 4 temporarily while fan and pump fire up before fault occurs

I did say power is cut in both these posts and all I know is the supplier for the board that he was talking to on the phone while I was there said not possible till tuesday so I dont know if his supplier is waiting for it too or what it is? I suppose if the supplier is waiting on a dellivery its not going to happen bank holiday Friday/Monday or on the sat/sun inbetween but either way I was happier to wait for him to bring the part to me warrented than to buy a "new" one from an online auction site and risk it being either non returnable or a duff waste of time.

Its not that the boiler only sparks once its actually sparks over and over again but with the time the a1 pin 2 and 4 is powered it would have only had chance to spark once if it was timed perfectly with the 240v on.

 

[fixter1]

ok at least you have got it sorted out now good luck

 

[chillyisons]

Thanks and I will post back Tuesday to let everyone know what the results are. Fingers crossed that the pcb ends this problem otherwise as previously mentioned it will end up being a gas valve too. The upside to all this is that by tuesday I will have saved one and a half weeks worth of gas which has got to be about £20😀 and the kids are enjoying having baths at grandma and grandads (easily pleased at 2 and 5 years)

 

[diamondgas]

Thanks and I will post back Tuesday to let everyone know what the results are. Fingers crossed that the pcb ends this problem otherwise as previously mentioned it will end up being a gas valve too. The upside to all this is that by tuesday I will have saved one and a half weeks worth of gas which has got to be about £20😀 and the kids are enjoying having baths at grandma and grandads (easily pleased at 2 and 5 years)

Hi CHillyisons,
Good way of looking at it regards saving gas ... It does sound like the PCB is duff!

Interestingly enough I've got my hands on a VK4105M gas valve and checked the resistances through V1 & V2 they are 2850 ohms & 1340 ohms respectfully! It may have different solenoids to the V4105A without investigating i would not be certain but I think they're the same. I was also reminded today that the molded plug on the valves carries within it some kind of wave rectification that alters the voltage. On the side of the gas valve is written 220/240Vrac. I was told once what it meant but it's gone to the ether for now! lol

 

[chillyisons]

Hi CHillyisons,
Good way of looking at it regards saving gas ... It does sound like the PCB is duff!

Interestingly enough I've got my hands on a VK4105M gas valve and checked the resistances through V1 & V2 they are 2850 ohms & 1340 ohms respectfully! It may have different solenoids to the V4105A without investigating i would not be certain but I think they're the same. I was also reminded today that the molded plug on the valves carries within it some kind of wave rectification that alters the voltage. On the side of the gas valve is written 220/240Vrac. I was told once what it meant but it's gone to the ether for now! lol

How dumb do I feel right now... very! Get ready to laugh your rear end off. My gas valve is also a VK4105M and I suddenly had one of those oh ohhh moments when I read your ohm results. After taking a quick peek at the multi meter it appears I had it set to 2K Ohm so I saw a breif reading before it maxed out on that setting and then showed zeros (School boy error😱). After reseting to 20K Ohm the correct readings are 2820 ohms & 1325 Ohms. Doh! but at least the valve is ok!!! Yay. So it would appear I have killed the PCB which is not so good but at least there is one on order. And that wave rectification that you mentioned clears up why I thought I was going nuts when 240v went in one end and 17v or somthing like it was comming out the other end. Awsome stuff and thanks for posting again diamondgas. Ill be back next tuesday to either jump up and down cos its still not working or to tell you I dont stink any more after having a hot shower.

 

[diamondgas]

Many a £120 gas valve has been changed because of a fault in the £20 rectification plug! Tuesday will tell all.... 🙂

 

[chillyisons]

This boiler has been sent to test me! Gas fitter chap came wednesday morning and was here for an hour and a half. PCB changed and now the boiler lights for both CH and DHW however when on DHW preheat the flame lights and you can here a noise like the water may be boiling a bit like a kettle and the flame is cut before it is at its temperature and then relights three seconds or so later to continue to its preset heat which happens 2 somethimes 3 times. When DHW is running (e.g the shower) the flame will be cut for 10 seconds or so every 1 minute with the hissing boiling noise just before cut off then relights the result is a cool flow of water in the shower untill it relights (Wife not happy😡). The CH side is worse than DHW as it lights for three seconds then goes off for three seconds and does this repeatedly until upto set temperature. It sounds like a faint hiss and a boiling sound fractionaly before cutting out. I have removed the CH return filter which was a solid black tube and is now a silver gause tube. I have removed the CH flow which had no filter in it but as it drainded through the flow side the bowl collecting the water was full of black bits of scale. I have checked the new diverter valve diaphram on the CH side which was fine other than more scale behind the diaphram. Boilerman says replace the boiler which is £1600 with a powerflush 🙁 You will probably tell me off for trying this but I got my wife to watch the cooker hob flame while I partialy closed the gas tap on the meter outside until the flame got smaller and then tried the boiler again. The flames through the viewing glass were noticeably smaller but the CH still cycled every 3 seconds. The pressure guage goes upto the red pressure line and boiler man says expansion vessel is shot and the high pressure may have damaged the heat exchanger??? At least I have hot water again... kind off. Im starting to think that the boiler man is right and its new boiler time.

Forgot to add.... When it hisses and makes a boiling noise the temperature lights dont jump up high quickly. They slowly increase as they would on a normaly functioning boiler that is running constantly its just that ours is on for 3 secs off for 3 secs. Also both CH isolation valves are fully open.

Little update.... Just checked to see if there is a part number on the new board so I could check its the correct one for the boiler and cant find one on it I also found that the electron coil is hot. Its not boiling hot but to hot to touch for more than a few seconds and ive got fairly tough hands. Is this normal or have I got another duff board? Board came in a genuine parts for baxi.potterton.valor.main box and the only code on the box is on a little sticker that says Aston 98/155772 POS-155 F13

 

[diamondgas]

Hi Chillyisons,
It does sound like you have a pretty choked up boiler. Your description resembles real poor ciculation going on through the boiler. That could be a choked up pump, heatexchanger and also could well be that the plate heatexchanger has also been effected. Most likely has!
Your 'Gas fitter chap' sounds like he's giving you good advice and a reasonable price too. You could have the system flushed alone and see if that sorts it out. Without experiencing the state of your system it's not one for me to call. Past experience with flushing tells me it has its limits & you could still be faced with having to change components/boiler once the system is freed of its detritis!
Regards your PCB; To me it's a load of thigs stuck on a flexible plate with other stuff here and there! It has dry joints that you find in the back and I can recognise the relays on them or hear them clicking, but if they're bust you replace them! An electronics expert I am not 🙂 If things on them get hot then maybe they're supose to *shrug*