Alpha CB24/CB28 Hot Water Issue

bodminman · 13 Feb 2006

Hi there, was wondering if someone could point me in the right direction.

Basically the heating on the system works fine, but the hot water will not work independently. ie: I only get hot water when the heating is on. So after the heating has finished it's bit (on the timer) I can go to a hot water tap and all I get is stone cold water. Yet if I manually turn the heating on and turn the hot water tap on, the water comes through nice and hot!

Is it the DHW Diaphragm?

Please point me in the right direction!

chrishutt · 13 Feb 2006

Is it the DHW Diaphragm?

Yes, or the equivalent in that boiler (e.g. flow switch). You need to look at the manual and fault finding guide - may be downloadable from Alpha web site.

bodminman · 13 Feb 2006

Will keep you posted on what I find and how I get on.

Could it be a DHW Switch?

Is it a straight forward job to replace?

Will I need a plumber?

Thanks again

chrishutt · 13 Feb 2006

Is it a straight forward job to replace? Will I need a plumber?

It depends on your ability with such things. In most cases it's fairly straightforward - just a matter of undoing nuts and screws, although I don't know this particular boiler.

bodminman · 14 Feb 2006

Removed the flow switch and pressed it in a couple of times and the boiler responded to what I was doing. Does this mean that the fault could still be the switch or could it be something else?

Thanks

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Mantamad · 14 Feb 2006

The Alpha CB28 boiler we had in our last house had exactly the same fault as yours, a new flow switch solved it.

ChrisR · 14 Feb 2006

Start with ch off and pipes relatively cool. Turn HW tap on full. Use the switch you have removed to turn the boiler on and feel the ch flow pipe (rightmost pipe). It shouldn't get warm. If it does you have a faulty diaphragm/diverter valve.

bodminman · 15 Feb 2006

Basically have narrowed it down to the diaphragm.

Started working throught the manual on how to replace the bugger but have trouble when getting to the undo unit bolts connecting to the heat exchanger.
When I do this water comes flying out even though the supply is cut off and the drain point has got to a very slow drip! Is this normal?

ChrisR · 15 Feb 2006

Not when you do it right...

You don't need to remove the boiler (b******r?)
Or the diverter valve
Or the dhw flow valve - though that might be easiest for you.
You only need to take the dhw flow valve apart.

Remember "we" have funny little tools...

bodminman · 15 Feb 2006

Thanks to everyone who's had a imput here.

Basically I've just replaced the diaphragm and now have instant hot water once again. It took me just over an hour and was just a little more patient than I was on my first effort.

I wouldn't have done it without the help from you guys on this forum!

THANKYOU

pilotdavo · 22 Feb 2006

I seem to have a very similar problem with my Alpha CB28 (4 years old). The CH works fine. The DHW is tepramental. It is impossible to know when it will work or not.

I have read through the above postings and just want to try to pin point the problem with my boiler. When I turn on the hot tap and there's no hot water it seems to me the boiler isn't heating water (no signs of exhaust at the flue and no noise of ignition at the boiler).

Does this sound like a DHW flow switch problem or is it the DHW diverter valve?

Is the diverter valve aka the diaphragm? Or is the diaphragm the faulty part that needs changing inside the diverter valve?

Any help greatly appreciated before I continue with a repair.

PD

bodminman · 22 Feb 2006

Hi PILOTDAVO

Basically, when my boiler was firing up to heat up the radiators I had hot water. And when the boiler stopped doing the heating bit the water from the hot tap became cold again.

I had a hot water tap running, removed the flow switch and pressed on it several times and each time the boiler responded and heated up the hot water. This to me indicated that the switch was OK but the diaphragm wasn't! (DHW flow valve) When the diaphragm was removed, it had a hole in it the size of a pea so obviously couldn't do what it's meant to do.

So removing the 'DHW Flow Valve' and replacing the diaphragm within sorted out my HW issue.

Hope this helps!

pilotdavo · 22 Feb 2006

I think I might have a slightly different probem then. The CH works fine. The DHW also works fine most of the time. When I lose HW it makes no difference if the CH is on or not it seems. I'll follow the same diagnosis as you and see if I have a faulty switch or bust diaphragm.

Was it an easy job to open and replace the diaphragm? Am I correct in saying it's located in the diverter valve?

Thanks for you help.

saffydude · 19 May 2007

Hi Pilotdavo

We've got the same fault with our 4 year old Alpha CB28 boiler... what was the fault with yours in the end?

It's been suggested it's the diaphragm or flow switch?

Thanks

bodminman · 19 May 2007

Hi there, I sorted out the initial problem by replacing the diaphragm. This game me back the hot water on demand for several weeks. Then the problem started again but this time I just replaced the flow switch and haven't had any trouble since!

I think I paid £15 for the diaphragm and around £30 for the switch from the local plumbers merchants.

Good luck!

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Alpha CB24/CB28 Hot Water Issue

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