Alpha CB28 Hot Water Problem

[Mick10256]

Hi Guys,
called to investigate an intermittent 'no hot water' on the above so went armed with a new clip on microswitch thinking nice quick job to end the day. Wrong! Opened tap and pulled switch off boiler fired fine so me thinks diaphragm as pin seemed not to be moving. I've overhauled diverters before so no problem there. The problem which bothers me is that the plate HS gets hot, very hot, when the hot tap is opened but the water flows cold. Can anyone explain, 1. how the plate HS can get stinking hot but the water flows cold and 2. the pin from the diaphragm isn't moving to operate the switch but is diverting the primary flow. When the tap is closed the plate HS cools down so not a stuck valve! I'm assuming this is simple diverter where the pin from the diaphragm operates the flow switch and also activates the diverter valve plates. Anyone noticed this before with a simple diaphragm perforation? Thanks in advance.

 

[Alpha man]

Does the flow or return get hot when the hw tap is running?

 

[Mick10256]

Do you mean CH flow and return? Hard to tell at the time. Young kids so CH on full blast no time to let it cool.

 

[Alpha man]

Yep, I do, it will be either the divertor or the dhw heat exchanger at fault.

 

[Mick10256]

Hi Alpha Man, the bit I don't understand is if the diaphragm is split, which I don't know yet, how the, we call them shuttle valves, is moving and heating the plate HE without operating the flow switch. And why the HE is very hot with a full flow of cold mains water running through. Very scaled plate HE? This is a very soft water area and it was intermittent until today so baffled! Before I order bits would like to understand and guarantee a fix.

 

[R1CKY]

Could be that the diverter itself has seized partially open to the PHE. Heat will bleed through to the PHE when the heating is running, as soon as you run the tap any heat in the PHE is gone and it can't regenerate fast enough.

Just a theory!

 

[Mick10256]

Cust opted for new Alpha part. Old diverter on my bench awaiting autopsy. Diaphragm perforated but why the valve moved?? Will report any findings.

 

[Alpha man]

The paddles will have carbon on them, so it doesn't close the ch port off fully, hence causing let by when the hw is run.

 

[CM25]

Just had exactly the same on a friends cb28,new diverter valve and works a treat..... Was stuck in mid position