alpha cb24 combiboiler problem

[stedge]

hello all,
my alpha cb24 fires up on its own heating up the radiators even when the heating is switched off. the only way to stop it is to swith off the mains supply. is this a flow switch problem or a pcb problem? Can I test the flow switch?
Any help would be much appreciated.
Steve

 

[Kristoflampie]

Yep you can test the flow switch..... Detach the plug in wiring to flow switch . If hot tap off there will be no continuity across blue and brown wires on switch side. If there is continuity when tap off the switch is faulty or sometimes loose in its clip and constantly firing up the boiler as if a tap is open. Switch should make and break in response to hot tap opening and closing when working normally.
Hope this helps

 

[Gas2Air]

The diverter on this alpha rests in CH. The flowswitch detcts HW flow from tap and diverts. I would suspect faulty diverter OR more likely external controls, ie timer that is giving demand, check backplate or timer for dampness/moisture.

 

[stedge]

Thanks, will test the flow switch. I have already tested the timer and that seems fine.

 

[Agile]

I am told the switches sometimes fail but not found that myself yet.

A common problem though is the diverter valve sticks and does not retract when the DHW demand is ceased.

You can remove the switch and watch the groove in the shaft with an inspection mirror and see if it moves prompty and returns to exactly the same position when DHW is taken. While the switch is off you can manually operate it to see if it appears to be working properly.

Tony

 

[stedge]

Tested the flow switch. it gives continuity no matter what i do with the hot water tap. When I take it off and test it it gives continuity, then when i press the button it goes open circuit. Is this right? Is the flow switch faulty?

 

[Agile]

A common problem is the diverter valve sticks and does not retract when the DHW demand is ceased.

You can remove the switch and watch the groove in the shaft with an inspection mirror and see if it moves promptly and returns to exactly the same position when DHW is taken.

Tony

 

[gas4you]

Is the little white plasyic 'push rod' still in place when you look at the flow switch ?

I've had several where these must have broken off, as they had disappeared.

Buy a new flow switch an fit it.

 

[mehran]

them microswitchs are waaaaaaaaaaaaay over priced. it takes the biscuit when they try to charge you silly money for a micro switch

 

[gas4you]

Usual Alpha rip off, £45.30 + VAT retail

 

[mrgas]

or could be primary thermistor failing fooling the pcb into thinking the boiler may freeze?

 

[stedge]

Are the £25 ones off ebay just as good? The white plastic bit is still there but as I said earlier, the switch gives continuity until the switch is pressed, then it goes open circuit. Is this the right was round?

 

[mrgas]

that is the correct way round. Try refitting switch and checking continuity at plug end with plug disconnected from pcb and power off. I think your switch may be ok. Has your hot water been unreliable?

 

[stedge]

the switch when it's fitted is closed circuit at the plug no matter what I do with the hot water tap. The hot water was unreliable a while back, had to turn the tap off and on a few times before it worked, but it's been fine recently.
what do you think it might be?

 

[mrgas]

if the switch works 100% when not fitted to diverter valve and not at all when fitted to div valve then your diaphram/diverter valve is faulty. However this would not make your heating come on when not called for as stated at the beginning of post.It would only make your hot water not work.
Did the heating come on when hot water only selected at switch on front of boiler?