"DeeBee" wrote in message
.uk...
I have googled around this evening but cannot find any leads to this
problem

Boiler is a Ariston EuroCombi SX20MFFICE, very common when iI fitted it
about 7 years ago

Now recently it has had a few problems..
Expansion Vessel lost its pressure, but managed to re-presurise it before
Christmas and it has been OK ever since.
Recently it developed a leak and that was traced to the main flow switch
which I replaced on Friday. At the same time I drained the whole system
down and added CH cleanser as the primary circuit water was somewhat
black. The system has always had inhibitor in.

Now the new problem is that when drawing off hot water (DHW), the boiler
is noisier than it used to be and the noise I can only describe as a
rumbling noise like a fan or motor with a knackered bearing, get worse the
longer water is drawn off. But when the hot tap is close the noise turns
into a kind of shuddering noise briefly, but it is quitet load. There is
obviuosly something wrong. Not sure if it is trapped air, but I have had
the auto vent valve open and have tried beeding of the temp sampling point
just before the heat exchanger. The noise is not present when the CH is
running, only when drawing off hot water (dhw)

So ant other ideas from you knowledgeable folk ???

TIA

DeeBee

Partly obstructed circuit for the boiler water. Has your model got a
diverter valve? Its likely the cleanser has dislodged crap from elsewhere
which is now lodged in the diverter or the domestic heat exchanger.
Whet cleaner did you use as a more "potent" one may be of of assistance or
you may need to strip down and manually clean out the appliance.