Alpha CB28X - Is my Diverter Valve Assembly Broke?

julesg007 · 19 Jun 2008

Hi All,

Looking for some help and guidance.

I've have this boiler for a number of years, about 5, and all's been fine until recently, when I started to have problems on DHW side of the boiler.

Noticed that I was not getting HW at one of the taps (1st floor about 20ft away from boiler) but put this down to the pipework being a bit resitricted up to a mixer tap but eventually the kitchen tap, being about 6ft away, stopped producing hot water.

Called in my plumber and he advised that the Diverter Valve Assembly was knackered and need replacing. He diagnosed this was the problem as with the hot tap running, the central heating pipes started warming up and I had noticed warm radiators when they shouldn't have been as the CH side was not running at the time.

There was also a small leak from the jointing nut between Heat Exchanger and above the DHW flow valve, although a tweak on the nut sorted this out but it has left an amount of limescale down the outside of the DHW FV and underneath it.

I would use my plumber to sort out the problem but he has become unavailable, and I know finding another one can be rather difficult.

So, is the DVA finished, or is it just part of the assembly or could it just need a service?

Also, are any of the above options really a DIY fix and if so where would the best place be to obtain the necessary parts?

The CH side of the boiler works fine.

Thanks all for your help.

Regards

Jules

Agile · 19 Jun 2008

There are clearly issues associated with the diverter valve.

It sounds to me as if the two issues I can identify can be cured by replacing the diverter valve.

I would class it as a Haynes three spanner job ( out of five ).

I would hope to complete it within an hour to include a basic service check.

However, as there is so much work being done I would advise an owner occupier to pay me a extra £30 to remove and clean out the plate HE at the same time.

Tony

julesg007 · 19 Jun 2008

Hi Tony,

Thank you for the reply and appreciate your offer to help and advice.

I have been looking at some of the other posts for the CB28X and have noted various other comments as well.

Some of the comments refered to the DHW flow switch and have found that if I I hold it up under tension but not actually removing it, the boiler fires up and I get HW.

Does this indicate that the problem is perhaps with the DHW FS rather than the DHW DVA as a whole?

Regards
Jules

Agile · 19 Jun 2008

julesg007 said:
Hi Tony,

Some of the comments refered to the DHW flow switch and have found that if I I hold it up under tension but not actually removing it, the boiler fires up and I get HW.

Regards
Jules

Yes of course it will, thats its purpose!

Your two problems are with the diverter valve. The easiest solution is to replace it.

Tony

nickso · 19 Jun 2008

depends on how much time you have to muck around.

i would try a new diaphragm on its own first, you may be lucky and find its just a stretched diaphragm and the diverter seals are still ok. worth a punt if you have the time as the whole diverter isnt cheap. if you have even more time you could rebuild the valve with a seal kit to avoid buying the entire valve.

gas4you · 19 Jun 2008

Of all the Alpha CB series that I have been called out to because of HW problems, I have yet to find the DV assembly its self at fault.

I would go along with nickso's post by replacing the diaphragm first and also checking the flow switch (1 minute job).

Make sure you get the Alpha kit though as this includes the seals for the plate HE, as this has to be removed to replace the diaphragm.

julesg007 · 19 Jun 2008

Hi nickso & Dave,

Thanks for the advice.

Was gonna ask if the DV is serviceable, seems that at least part of it is.

Was wondering how I would check to see if the Flow Switch is operating?

Jules

gas4you · 19 Jun 2008

Unclip it. It just pops off with minimum effort.

julesg007 · 20 Jun 2008

Hi Dave,

Thanks for the reply.

FS is working, unclipped it with the HW tap open and the boiler fired up straightaway and when I pressed the button in it switched off.

Now to get a diaphram kit.

Would you recommend doing anything else whilst I have the boiler open and the DVA out?

Jules

Agile · 20 Jun 2008

gas4you said:
Of all the Alpha CB series that I have been called out to because of HW problems, I have yet to find the DV assembly its self at fault.

I would go along with nickso's post by replacing the diaphragm first and also checking the flow switch (1 minute job).

Make sure you get the Alpha kit though as this includes the seals for the plate HE, as this has to be removed to replace the diaphragm.

The OP says that the rads get hot on DHW although the boiler does fire up. That implies to me that the manifold section may be sticking.

It could be that its not moving quite far enough of course but as this is not one of the easiest diverters to work on I would usually replace the whole unit if the rads are getting hot.

As far as I can remember its very difficult to replace the diaphragm without taking out the whole diverter. If taking it all out then its easier to change the whole unit.

Of course I operate commercially where time is money and my objective is to ensure my customers are assured of a further five years trouble free use.

For a DIYer with time to spare then changing just the diaphragm first may not be so risky even if it has to be taken out again. The problem then is that if the diaphragm does not fix all the problems then the whole unit may need to be changed.

Tony

nickso · 20 Jun 2008

from a cost point of view its better to change the seals and not the entire thing.

even if you do buy a diaphragm kit and end up replacing the entire unit you will have a spare diaphragm for next time.

julesg007 · 20 Jun 2008

Hi all,

Thanks again for all the advice.

Can understand looking at the problem I have from a commerical point of view and thus can see why my plumber stated that the whole unit need changing.

As a DIY'er, fortunately I do have the time to devote to just changing the diaphragm (and I will have to take the whole DVA out to do so) and I think that if the £21 paid for it sorts my problem I will consider myself very lucky. If, however, I have to change the whole unit, well that'll be a pain but I can live with it!!!

I would, however, like to ask for a little help. In the kit there is a small tube of what looks like grease or silcon, was wondering what it actually is and its application when changing the diaphragm.

Also, whilst I've got the boiler open and partially dismantled, is there anything else you'd recommend doing?

Have a good weekend and enjoy the football

Jules

Agile · 21 Jun 2008

As I have already said, cleaning the plate heat exchanger!

The sachet is silicone grease for lubricating the moving parts.

Tony

nickso · 21 Jun 2008

check and clean the prv and check the expansion vessel pressure. once you put it back together you will probably have leaks elsewhere on the boiler.....alphas are notorious for this, obviously repair them as the come along.

dont use the isolation valves to isolate the boiler from the system/mains as they will most certainly leak.

another thread reminded me of this, be careful with the two tiny screws at the bottom of the diaphragm, if they are corroded they may not come off easily and will probably round off so they become hard to move, i use a pair of grips to move them after lots of wd40.

julesg007 · 21 Jun 2008

Hello again Tony & Nickso

Thanks again for the help.

Almost got the DVA out - there is only a small retaining screw to free and it sohuld come out but it is solid so waiting for the penetrating oil to do it's stuff.

Tony, was wondering if the is anything else other than just rinsing the HE with clean flowing water to clean it?

Nickso, I am having problems releasing the room sealed cover, have undone the 4 screws as per the instructions, but it seems solid, is there anything I can do to try to release it as I don't want to damage to seal.

Was wondering how to check the expansion vessel pressure?, am only a DIY'er and don't have any specialist tools. Also presume the PRV is the pressure release valve?

Regards
Jules

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Alpha CB28X - Is my Diverter Valve Assembly Broke?

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