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Alpha cd28

Discussion in 'Plumbing and Central Heating' started by Jezzy, 21 Dec 2006.

  1. Jezzy

    Jezzy

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    Been called out today to an alpha cd28 which gives off cold water about twice a week and won't get hot. The rest of the time its ok, but the owner isn't happy with it. How can you diagnose an intermittent fault. i'm guessing its a faulty DHW thermistor? Any suggestions?
     
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  3. Agile

    Agile

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    Maybe you need to use more lateral thinking?

    Which days of the week?

    Could washing on a line on Mondays and Thursdays be blocking the flue?

    Much more likely to be a combustion problem as a sensor would be more consistently intermittent.

    Tony
     
  4. Jezzy

    Jezzy

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    Definately not - its the penthouse flat in a block of flats. you oughta see this place, its gotta be £500,000 worth of flat at least. This woman never washes anything apart from herself and when the boiler won't give hot water, i'm getting the blame. But seriously, how CAN you diagnose an intermittant fault? if your not there when its happening, its only guesswork. i suppose it has to be a combustion problem in as much as the boiler isn't firing up for DHW a couple of times a week, but what could cause this? could it be a dicky pcb? i'm not familiar with these boilers but the sequence of operation is the same for all boilers. Does anyone know of common problems with Alphas?
     
  5. Agile

    Agile

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    I find that very carefully checking each part and particularly resetting the gas valve min/max will usually find or eliminate intermittent faults.

    Tony
     
  6. Paul Barker

    Paul Barker

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    Do you mean CB28?

    DHW flow switch part no. 3.013211

    No need to drain down, unclip it make sure new one is clipped into the hole properly.

    To test, you here it click when making for hot water, so keep calling for water 100 times if you have to, on off on off on off, until you hear the click but the boiler doesn't fire. If you don't hear the click then it's the diaphragm, but 19 times out of 20 with your symptoms it is the switch.
     
  7. Jezzy

    Jezzy

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    Thanks for that suggestion (all). The boiler is in a cubby hole upstairs and the sink is downstairs in the kitchen and bathrooms. I can't shout loud enough for her to be able to hear me (its that far away) for me to say on off on off etc but i'll check out that part and give it a try next time she whines about it not working. its gonna be after chrimbo now and i'm going away (just in case she phones a call out).
     
  8. Paul Barker

    Paul Barker

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    turn the tap on go to boiler and use the screw slot isolation underneath to test.

    For what it costs change the switch anyway it's almost a dead cert.
     
  9. Jezzy

    Jezzy

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    Thanks for that one Paul. Looking at the manual (fig 23 page 23) the pic is showing 2 fixing screws. Are these relevant to the switch? The instructions say just to prise it up from the diverter valve body.
     
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  11. Paul Barker

    Paul Barker

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    No fixing screws it's horse shoe piece of plastic that clips over the neck of the diverter valve with a small white button in the apex that sits in a hole in the top of the diverter valve, this is srpung, so that when the diaphragm pulls the valve against it's own spring tension a slot in the pin allows the white protrusion to move in to the slot you hear a corresponding click as it locates, which proves the diaphragm is OK, but there is not always continuity made at the mechanical part proved by boiler not firing. Known fault on early boilers new ones are better we are changing them all as we go along, get a new one. They don't look a lot different but they are better.
     
  12. Jezzy

    Jezzy

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    Thanks again Paul. I'll try that next time i go. Got a problem with an alpha cb24 at another set of posh flats (not as posh as the first lot tho') neon 'b' is flashing every 5 seconds. Manual says either pump or pcb. pump is definately working. When i took the cover off the pcb it worked ok but when i put the cover back on, it started flashing again. i said it was an intermittant pcb fault and it needed replacing but he said he wasn't gonna pay the £134.84+vat for something i wasn't 100 percent sure about and ended up getting his own electrician to look at it. I think its fixed now but i never got any feedback as to what exactly was the problem. Again, do you know if this is a common fault on these boilers?
     
  13. Paul Barker

    Paul Barker

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    It senses pump operation by the speed with which the thermisters alter resistance, if it happens too quickly it either means that the pump is faulty the thermister/s are faulty (in dhw mode both thermisters are involved in the decision process, as during hot water operation the pcb monitors primary and secondary temperatures) or the boiler is overheating.

    So you have many things to eliminate before you buy a pcb.

    Might just need desludge/scaling.

    There again it could actually be the pcb. For me that is easy to prove as I have one, i would change the thermisters as a matter of course. If you ever see a blue thermister like used in Vokeras on an Alpha change it anyway the present white ones are much better made. The black or grey ones are good. There was another colour that is out of favour but i don't recall what it was, maybe green like aristons, don't quote me. anyhow black grey or white is what you want to see.

    Just thinking aloud as it's a grundfos pump head in your shoes I would try that anyway because a grundfos pump is no hardship to put back into stock if you were wrong. So I would try that and try the thermisters, then in my shoes I could also try the pcb as I hold stock.

    Actually if dealing with a boiler I don't hold stock for, when I have explored all avenues I do normally order a pcb, but I am normally wrong and now have quite a stock of pcb's which one of these days I will need.

    afaik Alpha pcb's are pretty good, though I did change one for a cd32c the other week when the fault said it was fan or flue. I got up a ladder and tookj the flue to bits, changed the fan, and finally had to change the pcb which is what it was. That was a swine, it happens to us all now and again. And of course it's a right parafenalia changing a pcb on a band a boiler. I still have to follow the destructions as I get in a cafudle but I suppose after a while I'll be able to do them off pat and then it'll only take 5 minutes instead of the 1/2 hour it seems to take me right now. I hve also found that some parts changers are not seting them up. When not set up a band a boiler grumbles and can harm itself. I've had to set up a few where someone else who I dare not mention (because local guys do read what I say on here) has changed a part.
     
  14. Jezzy

    Jezzy

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    You sound really clued up on the electrics side of boilers? How did you learn all this? Did you go on any courses, and if so, could you recommend one that i should go on? Whereabouts in yorkshire do you live? You haven't worked at PH Jones in Leeds have you?
     
  15. Paul Barker

    Paul Barker

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    I'm clued up on Alphas because I am the local repair agent for them. If I don't get it right I go back on my own time, that tends to focus the mind.

    My electronics background stems from designing from scratch and building high end audio amplifiers using transmitting valves, and being a radio ham, though I don't operate as a ham there seems little point to it, was just the electronics side that interested me not talking to old fogeys about such sintilating subjects as gardening and dental charges on a Sunday afternoon.

    I haven#t worked for a firm in Leeds but have done some work there, also go out to Knaersborough the Dales Harrogate and York for Alpha when they beg me.
     
  16. Jezzy

    Jezzy

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    So, do you work for yourself then or for alpha? The reason i am asking is cos we have a lot of flats with these boilers in them and i am not up on them. They are in the Halifax area though. If you let me know your mobile no i may be able to pass some work your way (if you want some)? If not, it would be good to know someone who may be able to point me in the right direction whilst i'm there looking at the thing and wondering what the problem is.
     
  17. Paul Barker

    Paul Barker

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    I work for myself, like Tony with Biasi, Alpha pay a minimum amount in my area to do warrantie repairs and anual services on boilers with a mainternance contract. I get better paid for work I find myself, but I prefer doing repairs to installs so I took this opportunity to get the pendulum swinging more in that direction. I need to approach other manufacturers to get sufficient repair work to be able to finish with installs alltogether. Scarborough is a very small isolated town you have to be parapatetic to get sufficient work, though I've never been short of work I spend a lot of time doing stuff I would prefer not to...

    I only travel for Alpha at the moment because they pay me more for doing so and only give me the jobs they can't cover, though I do go quite a distance for them, it wouldn't pay someone in Halifax to pay me to go there, but the mobile no is on my website best text me to say you want to talk.
     
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