Alpha CD24S losing pressure / high running pressure

[MadAlicesDad]

Sorry for the long post, but hopefully I've given all the pertinent facts.

I've got an Alpha CD24S boiler that was installed into an existing CH system in July 2004 along with a new hot water cylinder. The boiler has been serviced annually (last time Oct 2012).

After about 2 years of use, it failed to start one morning because the pressure had dropped too far ( there is a a very small weep from the tank). I topped it up to 1 bar and everything was alright. Since then, we've kept an eye of the pressure and had to top it up once or twice a year.

However, it's now failed three times in 6 weeks. This morning it was topped up to 1 bar (cold), but is now running at 3.6 bar (manufacturers data is max working pressure 2.5 bar).

Is this a failed expansion tank? If it is, Alpha state it is not possible to replace in situ (there is less than 45cm gap above the boiler). Therefore is it possible / acceptable to install an external vessel near the boiler, teed in to the heating return just before the boiler? Does the internal vessel have to be disconnected or just left in situ?

Another thing that concerns me is that the PRV is supposed to be set at 3.0 bar so how is it running at 3.6 bar (faulty gauge?); I cannot see any fluid in the overflow (but it is 15 feet up and it's dark outside). Does this mean the PRV is shot also? If so, can this be replaced DIY as it is not part of the gas system (there is actually a video on YouTube showing how to do it! http://www.youtube.com/watch?v=mQ-tT2PuXdU)

Mike

 

[ianmcd]

Sounds like your expansion vessel needs re-charged this should have been done annually during your boiler service but sounds as though it hasnt been done , there is loads of advice in the FAQs on here how to do it but you MUST do it correctly with a drain off point open or no point whatsoever in even attempting it

 

[MadAlicesDad]

Thanks for the quick reply. Is repressurising the vessel a DIY job? Is it fitted with a standard car tyre type valve?

I was going to give the installer a call tomorrow, but knowing his workload (not to mention cost!), was trying to scope out some options.

Mike

 

[MadAlicesDad]

I've read the FAQs and googled a it more and I'm confident I know what to do and have the kit to do it, but I've had a quick look at the top of the unit and cannot see the expansion vessel valve (it's about 15cm from the ceiling so access isn't great)

I'll have a better look tomorrow by removing some panels, but any clues to point me in the right direction to what has to be removed to get to it.

TIA

Mike

 

[ianmcd]

Hi Mike

Yes it is simply a car tyre valve (Schraeder valve is the correct name) at the top rear of your boiler there should be a strengthening bar about 2 " wide running the width of the boiler held on by I think 4 screws two at either side it is usually easier to access the Schraeder valve with this removed but make sure you replace it after topping the vessel up

 

[MadAlicesDad]

Hopefully it will be obvious - at the moment the airing cupboard is full of damp clothes so my examination was quite limited!
Cheers,
mike

 

[ianmcd]

just feel to the rear of the boiler about 2 inches or so from the wall and you should feel the bar I refer to, hard to describe Im afraid but should be obvious when you try

 

[MadAlicesDad]

I haven't removed the side panels yet - I hope this will give me access.
Do you know if the valve is on the top or the side?
Mike

 

[ianmcd]

you dont remove the side panels, the expansion vessel is between your boiler and the wall it is mounted on, appreciate if it is close to the ceiling that access is difficult, but you should be able to feel the bar I refer to at the very top of the boiler to the rear, removing the side panels wont make access any easier

 

[ianmcd]

SORRY thought your boiler was the CB just noticed it is a CD the expansion vessel on your boiler is inside the boiler and not to the rear of the boiler as earlier models were, you need to remove the outer casing and the expansion vessel is vertical on the left hand side and the schraeder valve is at the top the good news is your boilers one is much easier to access

 

[ianmcd]

instructions on how to available here

http://www.alpha-innovation.co.uk/custom/upload/instructions/CDS/CD S Inst & Serv Inst 01-11 .pdf

 

[MadAlicesDad]

Thanks, I've got that document. Although it says how to remove and replace bits and recharging is mentioned at 7.1, it does not explain how, or where the valve is!
Mike

 

[ianmcd]

The expansion vessel is the large metal container that sits vertically on the left hand side of the chamber and the valve is in the center at the very top of the vessel

 

[MadAlicesDad]

the good news is your boilers one is much easier to access

God help you if you have something more difficult than this!

It's behind (not to the left) and 5 inches down from the top of the boiler which is 4 inches from the ceiling; how stupid of me, I naively thought it might be accessible to human beings. It explains why the manual glosses over how to recharge it though.

Is this something that should be checked during servicing? Looking at the dust on it, it's never been touched. (sorry about the poor quality picture)

Untitled

• MadAlicesDad
• 2 Mar 2013
• 1

I can just reach it with the ends of my fingers, but cannot get enough grip to remove the cap. Looks like an external vessel is needed.

Mike

 

[MadAlicesDad]

All done, no new vessel needed after all . In case it helps anyone else, here's how...
I took a 6 inch piece of 15mm copper tube and crimped the end so it was a tight fit on the valve cap - I could then turn it from the top of the boiler and the cap came away lodged in the pipe.

I tried several bike pumps and foot pumps but couldn't get adequate access to the valve. In the end I used a car tyre inflator like you get at garages with gauge. This has a push on adaptor so doesn't need you to fumble around at the valve end. I put my garage compressor (set at 2bar max) on the patio and ran the hose through the upstairs window to the boiler in the bedroom.

I know not everyone will have these bits of kit, but it may point someone towards a solution.

System now running at about 1.5 bar when hot.

Thanks for the help.
Cheers,
Mike