biasi 24s no hot water!!! whole diverter valve changed :/

[dominicteg16]

hi im a gas safe registered plumber... im having real trouble at a biasi424s combi boiler.....Got me in an absolute pickle!!!

there was no hot water, so i changed the diaphragm, didnt work, then i replaced the gutts of the diverter valve, Didnt work either, Check small bore pipes for water and im gettting it.

The micro-switch etc is all fine because when i manually click it, the boiler fires.

I even went to the extent of a new complete diverter valve!!

ive ask other engineers about it and they have said the exact same!

Any comments would be greatly appreciated.... before i take this boiler off the wall and chuck it out the window!

thanks Dom

 

[twgas]

I think there's a venturi that operates the hw diaphragm, its just below the sensing tubes, near the pump, accessed by the nut on left of manifold.
See page 29. http://www.biasi.co.uk/images/manuals/RIVA/SERVICE/1199 EDITION.pdf

 

[GodKnows]

Does the primary ntc make ok? Often the pump on these are at fault. Check the plate hex isn't chocked with crap as well...

P.S. register with the "combustion chamber" as well. We GSR guys hide in there

 

[Slugbabydotcom]

I think there's a venturi that operates the hw diaphragm, its just below the sensing tubes, near the pump, accessed by the nut on left of manifold.
See page 29.

Had the same issue with a 105he. The right hand hydroblock looks to be the same set up. An exploded view of the venturi is on page 28
HERE

The venturi had crumbled with age so there was no pressure differential to operate the flow switch.

 

[Agile]

You have unfortunately focussed on the diverter valve instead of the whole boiler.

There are two simple tests you should have done:-

See if diaphragm unit pushes hard on DHW demand?

See if pushing pin on left of LH hydro block operates the demand switch and fires up boiler.

It is very rare for the venturi part to fail. It is also necessary to remove the gas valve to take it out so not a DIY job. It can also be very tight and needs a 24 mm six sided ring spanner or socket. ( The usual 12 sided ones usually just round off the corners ).

Tony