twin Vaillant 428's - odd problem

[Ted808]

Job presented as a leak- aav dribbling! Temp shut it- going back to replace. This is an open vented system, with twin Vailant 428 boilers. Anyhows boiler has F23 fault on - I reset and fired up... Made a helluva racket and went to F22!
Checked f+e ... It's full even a bit too full? I drained a cup off to check there's no blockage and water smelled like.... Well like poo?
Went back a few days later and boiler is OK and after resetting no noise or anything? So now it has water in it ( the f22 is dry fire...)
The thing is I noticed a weird thing on the supply from f+e to Chb ...about the size of a cup made of copper. I think it is a air seperator but couldn't get to it as loft is full up!!
My question are - How come one boiler is full and other empty? Both are supplied by the same feed from f+e after mug thingy... Why would the aav dribble? Why does the CH water smell like poo- I put inhibitor in a year or so ago. How come the boiler filled itself up? Lastly could the copper mug looking thingy have anything to do with it?
See photos above and below boiler... No photo of mug thingy!

 

[Ted808]

Found the thingy it is an air separator... I'm guessing they can block?

 

[chris watkins]

They can & do regularly, it's the low water velocity that allows the air to come out of solution also allows the dirt to settle.

 

[gassafe]

Yeah probably a restricted air separator... They seem to attract sludge...

Those lever valves shouldn't be on the boiler either... Take the handles off at least, if the customer gets a leak they'll turn every valve off on site & that boiler is then a bomb!

 

[Ted808]

Yeah probably a restricted air separator... They seem to attract sludge...

Those lever valves shouldn't be on the boiler either... Take the handles off at least, if the customer gets a leak they'll turn every valve off on site & that boiler is then a bomb!

Yes of course! Thanks