worcester 24i lighting and dropping out

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got called out to this boiler which fires the burner but drops out before the flame reaches the sensor at the back and continues to do this, also the solenoid has started to click in and out very rapidly before it fires, i've checked the aps fan and flue etc. I am thinking that it could be the minimum gas pressure set too low and wondered how to check this when the boiler wont run, is it just a case of turning the minimum pressure up a little and hoping it will run and then adjusting, or is there a better way to go about it. Also any other thoughts as to what to be checking would be much appreciated as I am recently qualified and am struggling with this.
 
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whats the voltage like at the solenoid while it is 'clicking in and out'?

What pressure reading do you get as it lights?

Yes you could try upping the ignition pressure slightly although becarefull as this will need re-setting when actual fault is found.
 
thanks for the reply rob884 will check those measurements when I get back to the boiler in question, but that won't be till after xmas now, will let you know what happens then, feel as though I am on a very steep learning curve at the moment and appreciate any help from you more experienced guys.
 
You have to ask yourself what the sequence of events is. Sometimes it isn't clear from the manual, so you have to ask the mfr, but most of the time it's not complicated.
I haven't checked this one in detail, but wouldn't you expect something like:

Volts go to gas valve
Clunk
and Sparks start
Gas comes out of gas valve and gets lit within a short time
You could check the burner pressure
This boiler has - as you have told us, a separate flame sense electrode. So it's going to take some time for the flame to get there. So the boiler will wait for a while after thinking it has opened the gas valve. I do remember how long it is but you're going to have to read the manual, then you'll remember! It's always a few seconds.

So which part of that could mean the solenoid cuts in and out (clunk) quickly?
NONE. So what can the gas pressure have to do with it?
So ask yourself what has to happen for the boiler to open the solenoid - or rather, why would it decide that it SHOULDN'T light?
You can work a lot out from the fault finding guide..
 
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ChrisR I was hoping that you (among others) might reply to this thread because I have learned a lot just from reading some of your posts in the past. You didn't disappoint me, that was a wonderful reply
informative and educational as well. Now I am going to think hard about what you said and see if I can come up with some answers. I already know that if the flame isnt detected it takes about seven seconds to drop out, but it doesn't even make it to the back of the burner, so I see what you mean about the gas pressure not being the culprit. this takes me back to the very rapid clicking in and out of the solenoid and now I am wondering (not great on electronics) if it may be a relay on the pcb or possibly a bad connection somewhere. Anyway thank you for taking the trouble to try and educate the less well informed, I am sure that there are other people reading this who will also learn from these kind of conributions.
 
Sure it could. So - as at line one, check the volts to the gas valve.
Trouble is with quickly-changing signals , cheap multimeters aren't very good, because the display doesn't settle. Analogue ones can be better. Personal fave is a mains neaon shoved into the back of the connector. Instantly shows high voltage or lack of it. (They don't work at 24V (WB might be that) though - could solder as resistor to an led I suppose...)
Digi meters like Flukes with an analogue bar are reasonable.

If the voltage is changing a lot, look for bad connections at the connectors and leads. Solenoids can also go open circuit when they warm up.
It's always worth measuring the resistance of a solenoid (disconnected). Sometimes the mfrs will tell you what they should be, or you can see if it looks about right for the voltage, eg mains ones are a few thousand ohms. Sometimes you'll see a discontinuity, with the meter.

I thought it was 9 seconds - memory not what it was...!
 
APS can cut in and out, the way to test that isn't the problem is to bridge the green leed and white leed quickly after fan has started (have a clip leed ready), but if that's hard some three leed aps boilers can be tricked by joining all three leeds. Don't know if this applies to 24i there are precious few worcesters in my neck of the woods so I haven't tried it.

I wouldn't suspect the coil of the solenoid droping in and out to the extent you are describing but it's always a possibility. I would expect total failure of the coil.

Double back to pump proving, does it do it in dhw mode? Pump proving is OK.(Because it's a bithermic/biflow primary heat exchanger, for which normally the pump doesn't run on hot water demand, but you might need to double check my assumption I'm not familiar with the intricacies of the 24i)

If it isn't the aps or the solenoid and the fan vigour is sufficient and aps sense tubes in order, fan stays on consistent, next place to look is dc output from board as Chris stated. If you can't sense that (as Chris described it's tricky but a made up led circuit would be ideal Watch board behaviour. is there any arcing or noise in time with the noise at the solenoid. The component doing that is suspect, probably in your case new board, or Raden board.
 
Any time a relay's involved it's worth checking the solder joints into the pcb.
 
Yes do you think the mechanical movement causes the dry joint?

Wouldn't it be a novel idea to use octal relays?
 
Yes do you think the mechanical movement causes the dry joint?

Wouldn't it be a novel idea to use octal relays? Oh what the heck and valve rectifiers aswell! Oh alright then sweep tubes instead of msofets as drivers. Valve based pcb's wouldn't mind the heat either.

I know I know your thinking of those old telly's you had to bang on top. At leats the tv engineer just had to have a brief case full of bottles and swap them over until it worked. Now with surface mount boards they are scared to touch them as just the very act of rmoving the board from the turrets can cause dry joints and damage delicate components, they change the board every time and with great care. We too have to be aware we can as easily cause the problem damaging the board plugging in and out the connectors or prising it off the turrets.

The boards in band a boilers are probably unfathomable, maybe raden will learn to cope with them, but I suspect we are going to end up like tv engineers, new board: bosh.

I know you don't beileve in prattling with the board though.
 
It's a new paradigm now, have you seen the complexity of the fan on the band A's? The band A pcb's have to set up pretty soon after lighting gas or boiler will damage itself and your analyser will need a new oxysensor.

Yes it's all change now.

You know what there are precious few pilot light boilers left round here, most of my calls are to band d's these days, won't be long and we'l all be wishing the band d's were still around.

We'll end up like tv engineers with a complex fan and pcb on the van, and an analyser to set them up.

I wander when they will design out the diverter valve with infra red or something.

Already an electroncis engineer is better qualified to fix a boiler, in actual fact at the current standard of the acs examinations it could be argued that corgi registered folk are not competent to work on gas appliances.

They need to get the assessment in step with the job.
 
thanks for the replies lads. although I must admit that a lot of what you (paul & chrisr) are discussing is over my head. I can identify with your last statement though paul, I passed my acs about four or five months ago and don't feel in any way prepared to go delving into most boilers, most of what I do know, I have had to try and teach myself through courses, books and sites like this. The acs exams require you to know how various gas valves work, and thats ok but its not much use if you don't also know how the control systems work. I suppose that what I'm saying is that there should be another level of training and qualification (which would include electronics), to seperate installers and repair guys.
 

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