Ed Sirett wrote:
On Fri, 24 Mar 2006 19:06:57 +0000, Gav wrote:


during a job on my placement, fault on ariston eurocombi, i think it was
a a23 or 24 mffi, no hot water but heating ok.

diverter valve? well the pin that contacts the micro switch was not
moving fast enough, if at all, to engage switch and thus boiler not
firing and water wasn't getting hot.

now this is where i was thinking instead of jumping in with a new
diverter straight away could we try to clean out the old one?
re install and it work. no, didn't work at all.

new diverter installed, still not going fast enough to engage micro.

then, just to prove a point to my self after following the small copper
pipes to the brass valve where the blow off is and using man's
instructions to idenify parts(cant remember what it's called)i opened
the boiler drain off valve a little. then suddenly the boiler kicked
into life and supplied hot water(the hot tap was on all the while in the
bathroom)

could it have been air trapped in the small capilaries that active a
large diaphragm on the diverter, or is it just some coincidence?

how would you have diagnosed the problem, bearing in mind the
boiler/heating was fine.

All this is a reasonable guess from just looking at the manuals.

The two models 23 MFFI and 24MFFI are very different. The former is an
older design something like a Ferroli and does not have a diverter valve
at all, its flow switch simply turns the burner on and the pump off.

Therefore you must have meant the 24 MFFI. Which is a condensing unit.
The diagrams for this show that the DHW flow is sensed by the differential
pressure across the DHW inlet filter. The diverter valve is motorised and
presumably controlled by the PCB.

I guess when you said that you changed the diverter valve you meant the
DHW flow switch. My guess is that you changed a good switch for a good
switch but got a result by bleeding the crud from in or near the entry to
the capilliaries.

This would be the water equivalent of a common problem found on the fan
proving system where crud collects in or near the entry to the tubes
leading to the APS.


in anut shell i thought the little tubes were most prone to blockage,
just detached and recoupled and it worked, for how long i dont know but
the customer was happy for a tenner + parts