Alpha CB28 no CH, but hot water mostly works

[davem37]

I've got an Alpha CB28 boiler and it has been playing up over recent weeks.

The first problem that it would cut out giving a red flashing light error. I'd reset it, and it would work fine for a while, providing hot water. I've not really worked out when or what causes it to trip over, as the boiler is in the loft, so I'm not going to sit up there all day waiting for it to fail. But it does occur a few times a day.

Now that the weather is turned I've now noticed the central heating isn't coming on. To remove any doubts about the thermostat I've bypassed that, so linking pins 1 & 2 on the input. So the heating should come on, but it doesn't. The orange LED blinks every 5 seconds as it should when happily resting, but the boiler isn't firing up to start the heating. It fires up for hot water fine when a tap is turned on though.

Over the past few years I've replaced the control board (due to some dry joints and worn out relays), the DHW switch, and the diaphragm.

Any clues to what I can check to narrow down the fault would be most helpful.

 

[davem37]

Looks like nobody has any clues.
I'm beginning to wonder whether it is the diverter that's stuck in the hot-water position? I've not read anyone experience this issue with this boiler online, but seen it mentioned with other boilers.

 

[DP]

Not that no body has a clue, it is just that the pros are busy with their daily task

Is the boiler firing when you call for heating?
Does the boiler recognise call for heating?
Have you looked at page 33 to see if you can add something to your post?

 

[davem37]

At least my prompt elicited a response - thanks for replying!
No, the boiler doesn't fire when the heating is called; it just ignores it and the amber light just carries on it's 5 second blinking.
I've had a look at the diagnostic flow-chart in the manual, and the symptoms I've got aren't covered in that.

I would have expected something to happen when heating it called, even if that something ends in an error code if something is faulty.

 

[mcmoby69]

Alpha?

New boiler time.

 

[davem37]

I decided to replace the diverter and did the DHW heat exchanger at the same time for good measure. And lo and behold I now have heating!
So the old diverter valve must have got stuck in the hot water position.
Hopefully this will be a bit of useful info for anyone who gets similar symptoms.