Noisy EuroCombi boiler - dhw only - any ideas?

[DeeBee]

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

[John]

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.

[DeeBee]

Thats a damn good point, it could be a lump of crud thats blocking the divertor valve (yes it does have one) I think I will call Ariston and get a recommendation for a more aggressive cleaner. If not I will have to strip the valve as the divertor is one of the most expensive parts on that boiler :-(

So much for trying to clean the system out.....

Cheers for that info...should have thought of that myself

DeeBee