Alpha CB 28 headscratcher... any advice chaps?

[theanalyst]

ok, so I went to a job last week, custard had just bought the house, unluckily for them it had an Alpha CB28 in it. She said it kept cutting out (heating, dhw was fine)so she would have to reset and then it would work again.


I told her to try it on DHW only mode until I could get there late last week. She reported it had been working fine for DHW only.

I tried it on heating, ran it up for a while till the system got hot and bingo, it cutout. Downstairs rads were blazing but upstairs cold. CHecked them, some moron had closed a lot of them off, so I was wondering if the boiler had reached its set temp and cutout. Adjusted all the rads, hunky dory, nice warm house. Left it running half an hour, all good.

I had taken a new CH overheat stat but they had supplied a thermistor when I opened the bag. I couldn't test resistance on current one as Alpha gives no resistance readings in their crappy manual. I checked the pump which I had expected to be the culprit. It was nice and free, spinning like a dream, so I thought it was cured...

Nope, just had a call saying it has cutout on her twice this weekend and I am scratching my head a bit... Thinking it could be the pump overheating, but if I cant get it to repeat it could be one of those nightmare jobs...

Anyone got much Alpha experience? I hardly ever get them, only know that they are sh*t!!
is it worth getting a new overheat stat before I go?:ack2:

thanks in advance

 

[theanalyst]

I did think about the primary temp sensor for heating flow as well, but again, got no readings as to what it should be and I don't like throwing parts at boilers ever. That's for British Gas!!

 

[Nostrum]

Blocked bypass maybe?

Was the heating water ok?

Try reducing the heating temperature to see if it makes any odds?

 

[theanalyst]

Blocked bypass maybe?

Was the heating water ok?

Try reducing the heating temperature to see if it makes any odds?

Internal bypass?

I turned it down when I left, seems to have still done it when Id gone...aaaggh

 

[theanalyst]

Sorry mate, missed the 'heating water' bit?

yes it got up to temp nicely, all was working as it should be and all rads were toasty for at least 30 minutes, until I had gone anyway !!

 

[Nostrum]

Internal bypass?

I turned it down when I left, seems to have still done it when Id gone...aaaggh

Yeah, just a thought if the system has a room stat. Did you follow the fault finding in the manual? Was it definitely locking out due to over heat?

Water clean or mucky?

 

[theanalyst]

Cheers!
No stat that I could find and custard wasnt aware of one. There is an old programmer under the boiler and then the boiler heat control for temp control. I suppose I could link out the programmer just to eliminate it, but it has to be worse than that!!

Fault finding in the manual seemed pretty useless. Didn't really give me any info that helped or that I didn't know(like resistance readings for overheat stat etc)

Water was dirty when I checked the pump, seen worse though! thanks

 

[theanalyst]

Yes, Neon 'A' is flashing the lady has kindly informed me! On checking the manual that means overheat stat has operated. Would be nice if it was just the OH stat, but....

 

[theanalyst]

Another thought I have had is if the PCB is goosed. There seems to be a few cases where OHS has indicated a similiar fault where engineers have ended up replacing the PCB. I will try a new Overheat Stat, then if the pump still seems ok I will have to look at PCB

 

[dave1]

I'd be going with the thermistor

 

[theanalyst]

Cheers mate. I have been doing some further digging and it seems that it could also be the Air pressure switch. Apparently that causes these symptoms!!? Will be testing that first job

 

[Millsy 82]

I used to work on quite a few and the thermistors seemed to be a bit of a problem the other bit that is definately a problem is the Pcb but they are expensive.

I did have the readings somewhere but I haven't touched one for a year so I have probably lost the scrap of paper I had it on.

There was a PDF list in the gas safe only list have a search for that and see if it's on there.

 

[ed209]

Aps

 

[gasmanrob]

There's a gorse filter in the return I think depending on valve type.

If it's the he check the flue stat if it's an se check the flue clamp.

 

[Alpha man]

Change the air switch!

 

[theanalyst]

Thanks guys.
It was the air pressure switch...!!! I tested it as soon as I got there, and it was sticking and not operating correctly at all....

So I replaced it (new one was about £65!!) and all is hunky dory Thanks for your input chaps

**one to remember that.

 

[bassmonster]

It was the air pressure switch...!!! I tested it as soon as I got there, and it was sticking and not operating correctly at all....

So I replaced it (new one was about £65!!) and all is hunky dory

How do you test the air pressure switch mate?

 

[stevetheplumber]

obviously thats fixed it but can anyone explain how an aps causes overheat stat to operate surely when it reaches temerature it should drop to low flame and then off

 

[Aquazone]

Yeah I dont think the OH actually operates, this fault normally happens when boiler stat reaches temp, APS stays made then when temp drops back down boiler sees APS already made and throws an error light up, but it's the same error light as OH - light B on its own iirc.

Had this fault twice now and was technical that told me about it. Nothing in manual

 

[Alpha man]

obviously thats fixed it but can anyone explain how an aps causes overheat stat to operate surely when it reaches temerature it should drop to low flame and then off

1,If the coloured sticker on the front of the APS is coming away from the face, it loses air pressure, causing the intermitant fault,

2, It's a **** boiler from the top to the bottom!!

 

[ed209]

Agree with "Aquazone" APS throws up un- written fault code that seems like overheat, had it quite a few times myself, I think Thechnical mostly read out the manual but sometimes you get one that has real world Thechnical knowledge and points you in the right direction.