Alpha CB24 Boiler - Heating But No Hot Water

[DanJR]

Good evening all,

We have just moved into a property but found we have no hot water from our Alpha CB24 boiler.

The central heating works fine but even when it's running the hot taps run cold. I have done some diagnostics but am now stuck...

- There is 24v across M5 terminal 16 and M6 terminal 20 on the main PCB,

- The DHW switch works when it is removed from the boiler (i.e. the burners fire when the switch is released and cut out when the switch is manually operated) but not when it is installed in the pipework.

Even when the switch is operated outside of the boiler pipework the hot taps still run cold.

This is leading me to think it is an issue with the diverter valve but I have no way of confirming that, does that sound likely given what I have described?

There is also a leak from the union between the DHW heat exchanger and diverter valve (it looks to be coming from the joint itself).

Many Thanks

Dan

 

[45yearsagasman]

It sounds like the diverter diaphragm. If your new property is rented, you don't say, then call the landlord/ agent. If you've purchased, then go back to the vendors. Not the easiest combi boiler for a diyer.

 

[DanJR]

Thanks for your reply.

We have purchased the property and have already completed so I think the cost of this one is on us. If I were to get someone in is this an expensive job?

Thanks again

Dan

 

[AGAS]

This is leading me to think it is an issue with the diverter valve but I have no way of confirming that, does that sound likely given what I have described?

select hw only and when running check ch flow pipe under boiler is getting warm/hot , this will indicate the diverter is passing and needs further investigating.
also as 45yeargasman says above ,

- There is 24v across M5 terminal 16 and M6 terminal 20 on the main PCB,

are you saying your putting one probe on M5 16 and one probe on M6 20 ?????? if so your measuring across two components at the same time???

 

[ianmcd]

It is the Diaphragm inside the diverter valve that has gone very common problem on your boiler, can be a real pain to replace it if you havent done one before

 

[AGAS]

better to change the whole diverter in your instance

 

[DanJR]

Thanks AGAS, I'll try that in the morning.

As for the voltage measurement, I was following the diagnostic flow chart in the installation/commissioning manual but got stuck at the point where it asked if the diverter valve spindle was moving.

I'm assuming the diverter valve needs to come out anyway to replace the diaphragm? How many hours labour (for a professional, not me!) would it take to replace the valve?

Thanks again

Dan

 

[ianmcd]

A pro will do it in an hour, if you are getting a pro then they will probably just change the diaphragm but you need to remove the complete valve to change the Diaphragm but nothing else to go wrong in the valve

 

[Gasguru]

This is no easy diy job.

The first thing to check is whether the vendor ticked the box on the solicitors paperwork to say the boiler was in good order...many vendors are happy to lie. If they said the boiler was fine you have a claim against them for repairs.

The diverter repair on these models can be a lottery. Given the water leaks the plate hex will probably have to come off. Therefore it's best to replace the whole diverter. Often the small grub screws have seized and that means drilling out or replacing the maniford section. It's also common to find the primary heat exchanger pipework will start to leak if they get disturbed....that means opening up the chamber (and the case seals tend to perish) which is not for diy. The diaphragm can also be replaced if the pump is taken out but that's guaranteed to make the primary hex seals leak.

Dog of a boiler.

 

[Agile]

Unless the Vendor is paying then it may be better to just replace the boiler. They were never very good.

Because of all the complications I would always replace the whole diverter valve on that model at a total cost of about £223. But that is £223 towards about £1800 for a new boiler.

Tony

 

[McCombi]

New boiler for a diaphragm job. Madness!

 

[Agile]

It is very hard work to replace just the diaphragm on that model.

But they are now pretty old and not thought of as very reliable.

Tony

 

[DP]

As mentioned earlier, layout of components a little haphazard, not forgetting leaks that appear when pipes are disturbed.

If boiler vitals are in good order, would suggest diverter overhaul ( not replaced but have replacement diverter handy if required), and o rings replaced and boiler will be good to go.

 

[nickso]

Piece of **** job....an hour tops for the diaphragm and the worst that can happen is the grub screws are stuck....you can even test that before you begin.

I think some of you balloons just want the diverter for scrap and 300 quid in your back pocket.

 

[DanJR]

Thanks for your replies guys.

Turns out that the diverter valve had failed so this has been replaced and we now have hot water.

Unfortunately, where the boiler had been leaking for so long the screws had corroded in place - meaning our boiler guy had to drill them out!

Hopefully the CB24 will get us through the winter at least

Cheers

Dan