Alpha CB28X Strange fault!

[Printerman100]

Hi

I have a faulty CB28X. I've been reading quite a few posts but no one has quite covered the issue I have.

When the boiler IS running both CH and DHW work fine. Both lovely and hot with lots of flow.

Thing is the boiler might run for say 30 minutes to and hour and then suddenly cutout. The lights do not show warning. The B light flashes slowly every 5 seconds acting as if it is actually just set to not run. If I run a tap there is no hot water or hot supply to central heating.

Then after a while the boiler will click into life.

Some times It clicks and cuts out after 5 seconds....sometimes it will run and just work as normal.

Its as if it faults when it gets up to temperature..

I'm not convinced its a diaphragm fault and when it is working I've also checked the DHW micro switch and that works fine too.

Anyone able to give me some thoughts on this?

 

[DP]

When was the boilers serviced last?

Combination boiler is a complex piece of machinary that requires regular service and maintenance. If this is not done, system components get sluggish to result in operation similar to yours

 

[Printerman100]

It was serviced a year ago.

I actually had the service engineer come and look at it but said due to it being intermittent he couldn't work out what was wrong.

He said he could service it but it was pointless until we knew what was wrong with it.

 

[ianmcd]

To be honest unless the indicator lights shed some indication then an engineer would have to be in front of the boiler when it faults to diagnose what is wrong but I would be looking at the primary thermistor if it hasnt been changed for a while it could be going open circuit at high temperature but would usually show on the fault indicator neons

 

[Printerman100]

Hi all,

thanks for help so far.

Right i now eventually have a proper fault.

Red light(A) is flashing and the yellow light (B) is also flashing at the same time.

Looking in manual it states a pcb fault or an air pressure switch fault.

I'm not going to be messing on with this but i can check the pcb myself. Looks straight forward with the wiring diagrams

If it is an air pressure switch fault is this easy to change?

 

[Gas2Air]

APS not switching back when hot.

Edit, no it isn't for you to change.

 

[Printerman100]

That is a fair enough answer.

Thanks for the response.

Its what i expected but thought i'd ask.