Alpha boiler frequently no H/W

apracing · 23 Aug 2006

Hi there! I'm seeking help with an Alpha combi boiler. It's about 4 years old and has been serviced regularly. When turning the hot water on, I hear a light whirring sound from the boiler but sometimes it doesn't fire up and I don't get any hot water.

If I reset the boiler then it works. However I'm now haveing to reset it quite often (every day). What could the problem be?

The water pressure is spot-on and the water temperature dial is turned up to about 7, but I get the same problem when it's on maximum.

Cheers,

AP

apracing · 23 Aug 2006

Forgot to mention that when it doesn't fire up the B light still flashes at 5s intervals as when it's on standby....

Agile · 23 Aug 2006

Does this problem happen at a lower DHW flow rate rather than a bath tap on full for example?

Tony

apracing · 23 Aug 2006

Tony, thanks for the reply.

I've tried the taps on with a low flow rate and also on full blast but it doesn't seem to make a difference...

AP

ChrisR · 23 Aug 2006

Is it a CB24/CB28?

The Whirring - presumably the fan. It always starts when you open the tap? Might be easier to tell from outside.
Does Neon A come on, continuous or flashing?

Are you saying you can run tap and it works, then it doesn't but does if you reset it - all in quick succession?

Just possible is the pump. If you drop the front and put your hand on the pump (round thing on the right) you would expect to feel it running. You can undo the central screw (dribbles) and insert a flat screwdriver to be sure. Twist screwdriver to unjam pump. They aren't usually intermittent though.

apracing · 23 Aug 2006

Hi there. I'll verify the model tonight.

I'll confirm the fan question in the morning too, though it probably is the fan. I can hear it everytime the hot water tap is opened.

I don't get A coming on at all. Just B keeps on flashing at 5s intervals.

Basically I run the H/W tap. When the fault happens, the water is cold from the start and the boiler never comes on unless I go and reset it.

I'll search for the pump tonight too...

Thanks for the help,

AP

apracing · 24 Aug 2006

Right:

Model is Alpha CB24

CENTRAL HEATING:

The central heating works absolutely fine.

DHW:

When I turn the H/W tap on the pump seems not to come on and also the fan seems not to come on. You can just hear the water going through the pipes in the boiler area.

These were my findings last night. Help!

AP

micky p · 24 Aug 2006

sounds like a problem with the diverter valve. probably either the diaphragm or microswtitch problem. You need to test to see it the microswtich works. if i remeber correctly pull the microswtich off the side of the diverter valve and i think the boiler should fire up (or push the button in once you have taken it off and see if it fires up, i can't remember if the microswitch works when pressed in or out so try both)... don't do this for long as you are telling the boiler you are drawing water from the tap when you arn't. If this works then there is a problem with the diverter valve or diaphragm. If it doesn't then it could be a microswitch problem or other elctrical fault.

ChrisR · 24 Aug 2006

Absolutely! Much simpler problem than if you really had got that whirring sound when you turned the tap on!

apracing · 24 Aug 2006

Thank you very much! I'll check it out tonight and post my findings in the morning.

Many thanks again,

AP

apracing · 31 Aug 2006

It was in actual fact the switch not working properly. I'm going to get a replacement today and hopefully that will solve the problem...

Many thanks again for the help!

AP

Tom. · 1 Mar 2007

Hi there

I've just started having the same problem these last few days. Turn the hot water tap open/closed a few times, and away she goes.

The boiler has been great for the last 4 years, no odd noises, no odd operation, totally reliable. I'm actually very impressed by it.

I'm minded to think its the switch as when you turn the hot tap on, you can sometimes hear the boiler switching 4-5 times before it kicks in.

Could somebody point me in the direction of the location of this switch? I do my own vehicle maintanence, so don't mind replacing switches and the like. If its the diaphragm or the valve, I'll leave that to guy that installed it (friend's father in law, CORGI registered).

Heres a couple of piccies to help:

The diverter valve is just to the left of the pump, is it not? Is the microswitch the small black assembly with the blue/brown wiring coming out from the top, in the centre of the second picture?

gas4you · 1 Mar 2007

Flow switch is the black little box with brown & blue wires coming out. (2nd pic more clear) Should just unclip off. Has a white 'plunger' in side.

Paul Barker · 1 Mar 2007

Yes that flow swicth in the picture should be replaced anyway even if it isn't the fault as it has been improved upon. The diaphragm is differential diagnosis.

The flow stich has a white sprung prong which hits a pushrod normally when the diverter valve is in it's natural central heating mode position. When water is run the diapragm sucks the push rod towards it so the white prong becomes lined up in a notch between the end of this pushrod and the start of the system water section of the diverter valve. The point where the two pushrods join is shamfered to allow the prod to extend further. This extension should make the microswitch.

Before removing anything operate the hot tap while at the boiler, if no tap where the boiler is turn on a hot tap and operate it on off on off via the cold feed isolation valve. Listen to what is happening, in all cases if the diaphragm is in good order you will hear a little click as the prong dips down, operate the boiler many times to prove that this hapens consistently every time. If it does you have proved that the diaphragm is not the fault. Next, ask yourself does the boiler fire each time? If you ever, even once hear the click but the boiler does not begin the next phase (which is start the pump and the fan) you have a faulty microswitch. But as I said renew it anyway.

If the you don't hear the click, you need a new diaphragm.

You have grey thermisters, those are known to be good generally.

Agile · 1 Mar 2007

Am I the only one who is given a fit of giggles and wonders what Paul has been drinking?

Paul Barker said:
Yes that flow swicth
The diaphragm is differential diagnosis.
The flow stich
white sprung prong
the diapragm sucks
to allow the prod to extend
you will hear a little click as the prong dips
Next, ask yourself does the boiler fire each time?
If you ever, even once hear the click
If the you don't hear the click
You have grey thermisters, those are known to be good, generally!

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Alpha boiler frequently no H/W

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