Just collected my new combi expansion vessel and it's the wrong one!! I ordered it over the phone from my (reasonably) local supplier using the manufacturer's part number taken from the short parts list in the boiler's Manual/Handbook. All this without physically double-checking the part number stamped on the existing vessel's green label, partly because it's a bitch to access without removing a load of gubbins from the boiler first. The new one is rectangular in shape and of 12 litres capacity, and the manual even obligingly shows a diagram of it as being a rectangular part too. However, upon (much) closer inspection, the existing and faulty unit is a ROUND one of only 8 litres capacity, instead!
More confusingly still, the new one has the air/tyre valve located on the top of the vessel, instead of at the bottom on the same side as the CH water union. Nor does this tally with the diagram in the handbook, which although of the same shape (rectangular) as the new one, shows the valve to be in the same position as my existing round vessel, i.e. easily accessible from beneath the boiler. This means that, assuming it will physically fit my boiler, the valve will no longer be accessible from the top (unless you possess octopus tentacles) for pressure checking and topping up. :-(
I have already sent an email to to Vaillant tech support asking them to advise if I can substitute this new one for the old round one, without altering any of the existing pipework connections etc., but in the meantime I thought I would ask here if anyone should know why the air valve has been relocated?
Also, as I mentioned earlier, the existing round unit is stamped as having an 8 litre capacity, whereas the new rectangular one is stamped as being 12 litres capacity. If this (unannounced) specification change from a rectangular to a round one is bona fide, then why would they also reduce the capacity of the expansion vessel? I would have thought more was better?
Pah! Nigel