Ariston Combi Boiler problem

I have a problem with an Ariston a/23 combi boiler that has beaten British gas and a handful of gas engineers. The system fires up and immediately fires down again and fires up again immediately and so on. Anybody any ideas? Various bits have been replaced but to no avail. Very occasionally the system works.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Contact Ariston and see what they say.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I'd second that, their tech people have been very helpful to me. They will probably recommend someone who has actually been trained on the boiler :-)
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

They tend to know all the scenarios that have arisen and can pinpoint the problem much quicker.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Hard water area?
Is the heat exchanger scaled up?
Is there a blockage in the system
Is the pump working properly ?
I'm afraid, to properly diagnose this, more info is needed
is it fully firing up or just starting - still sparking?
Has this suddenly happened or has it been getting progressively worse?

--
geoff

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Thanks for the reply.
It is a soft water area. Very unlikely the heat exchanger is scaled up, as it is only 2-3 years old.
No blockage in the system since it has been known to work.
Pump seems ok, when the system works.
It seems to be more or less constant now, from an intermittent fault. Apparently the gas engineer is now going to replace the heat exchanger. Its a friend of mine, but it seems to be a case of just trying things. I'm not a gas engineer, but I wondered if the thermostat that tells the temperature of the heat exchanger could have gone, so it thinks its hot and cuts off, but then there would have to be another thermostat that tells it to fire up again. It does fully fire up, as far as I can see. I don't know whether the spark stops.
I'm getting near to the stage to say get a brand new unit.>

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

...
That was going to be my next question after eliminating the obvious ones. IF the temp sensor has gone off, then it could be still working in a borderline fashion, but then you'd need to be able to measure the resistance (IIRC about 10k at 20 degrees, about 3k when it's up to temperature

Well, you know the little click, click, click, woom (so to speak) you hear as the boiler ignites, well if it keeps on going click, click, click ... click, click then it's not sensing the pilot being alight and will stop and try again (I think ... I can't remember on the Ariston exactly)

--
geoff

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

=================If this was a carburettor in a car I would say that there was a bit of loose grit periodically blocking the main jet. Your problem might be similar - a bit of loose grit or scale might be blocking the the main jet / injector. Have you tried removing and cleaning the main injector / burner?
Cic.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Is the high gas coming on blowing the flame out?
Is the high gas coming on blowing the flame away from the flame sense electrode?
Dicky relay on the control board ?
You don't say what bits have been replaced
--
geoff

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
What do Ariston say? It should be/must be, a known problem.
Hugh
--
----------------------------------------------------------------------------
---------
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.