Those Pesky Italian Ariston Combi's (23 MFFI)

[geoffpidge]

Hi Guys.
Could anyone shed any light on a problem I have with the DHW on my 1 year old Ariston MicroCombi 23 MFFI. The CH works a dream, comes and goes as it should however i have really bad flow on the DHW side. I am getting 6L/Min on the cold water feed to the boiler but only 2L/Min on the hot. I have dismantled the flow and return of the DHW and it seems that there is no blockage in the pipework. The olny thig I can think of is that the "Twin Pass Heat Exchanger" may be furred up as we are in a hard water area. Could it ve anything else? I have checked the water circuit diagram and it seems the DHW does not go anywhere else apart from throught the "HE" Is there a flow restricter inside the boiler?

Any help would be greatly recieved, especially as my wife is giving me an ear bashing as she cant wash her hair properly!!

 

[EliteHeat]

Almost certainly the heat exchanger, but why on earth did you have a combi installed with such a pathetic mains flow rate?

 

[chrishutt]

If you can only get 6 l/min on the cold then it's not surprising that the hot flo0w is so poor. You need to investigate why the mains pressure/flow is so hopeless and try to correct that. Are you sure it's not fed from a tank?

 

[Gasguru]

Are you really in Italy? There are several versions of the Microcombi, all the UK spec versions I have seen do not appear to have any flow restrictor or filters on the cold inlet (seperate cold inlet and return connections).

However there are versions (with a brass manifold incorporating both the cold inlet and the heating return connection) that appear to have a flow switch shuttle complete with filter (and perhaps restrictor) behind the large brass end cap.

As previously said investigate problems with poor pressure/blocked stop cock etc.

The bithermal heat exchanger on these boilers is however sensitive to particular water types and could also be suffering from scale as previously mentioned.

 

[geoffpidge]

Sorry, i should have read my "pest before sonding it". The mains pressure is about 26 L/min not 6!! We have an 800 Litre cistern tank and a pump to maintain the pressure to the house as the pressure of the "town" water supply is only about 1 bar at best. I have managed to find a copy of the "Exploded view" [http://www.harrian.com/Prod_info/info/ariston/ariston_current/ariston_current_boilers/microcombi23_mffi/microcombi_23_mffi_from_2320033400001_to_2320101500001.pdf] on the internet and it does seem that the HW circuit is completely seperate from the CH. I have noticed that when the HW is left alone (not drawn) for a few minutes, the pressure seems to build up - assuming the expansion vessel is filling - and when you draw hot water it first runs very fast and then drops to the 2L/min. Obviously the pressure is not enough to fire the boiler. I plan to take the HE apart today and check for blockages etc. I will keep you posted.

BTW we are in Italy, weather is fresh but lovely clear blue skys, still warm enough for no coats and the CH only went on on Monday - oh how i miss London!!
Ciao for now and Grazie for all your replies.