Baxi Combi 80HE--HELP

[Cyberprog]

I work for a company that sells these expansion vessels - though they are the same part used over a lot of baxi appliances. We sell around 20-30 a year, they're made by a company called Altechnic in Italy. Not sure why they've condemned your boiler though - should be fixable?

 

[Seadog]

theres zero pressure in the system, been none since possibly Tueday eve, any attempt to refill/replenish, water gushes out from the ruptured Expansion vessel.

So lack of system pressure--is that why the rad vent didnt squirt when opened to "bleed"-- I was only curious if there was any water left in the upstairs system-- there was insufficient on the floor to have emptied all the rads, but todays enginner isolated all the valves underneath the boiler?-Gas, cold feed water in, CH in, CH out, HW. all turned off, electric left off- I turned it off on Wed am. If he did damage the vessel pipe maybe he had to turn CH flow/return off to stop it escaping?-- I dont know

Stan

Stan, first off I'm not a central heating engineer but have worked on quite a few domestic systems with my friend who is Gas Safe qualified, as well as having installed quite a few in the past when the regulations weren't so stringent. In no particular order, here's my take on the problems.
From your first image it seems that the left hand side of the expansion vessel is still straight, hence the alignment of the vessel and its union have not been affected. It would seem that the engineer has strained the union and opened the joint in the pipe. Had the pipe failed then the vessel should not have.
For the vessel to fail, the pressure in the system has probably exceeded 5 bar. This is worrying because the pressure relief valve (PRV) is set to operate at 3 bar. The PRV is attached directly to the manifold at the rear of the pump so it is very unlikely there could have been any blockage in the port. I would doubt very much that the valve is faulty, they are a safety device and must work. If anything they usually fail in the open position due to constant over-pressurising of the system causing water discharge and debris to stick on the valve seat. As has been suggested there would seem to be a blockage in the vent pipe from it. The vent pipe must always be run outside: A) because it can discharge near boiling water and B) it gives you an indication that things aren't right with the system.
Also, as mentioned, if you open a bleed valve in a radiator with pressure in the system you will get water squirt from the vent. If this didn't happen then there was no pressure in the system. This is worrying too because all combi boilers have water pressure switches that will prevent operation if it is low (normally below 0.5 bar), so there seems to be an issue there too.
A bursting vessel will dump the water within the vessel plus most of the water in the heat-exchanger due to dissolved gas in the water bubbling out when the pressure is instantaneously released. The rest of the water in the system will trickle out over an extended period of time but it is likely that the majority is still in the pipework and rads.
The boiler is probably repairable but whether or not it is worth it I cannot say, and the existing installation is in need of change re the PRV vent. For example there is a new expansion vessel currently on a well known auction site at £100 new, other spares are probably as easy to get hold of. I've fixed many so called boilers that have been written off by the likes of a certain gas supplier, for example, it's always in their interest to sell an new unit and then try and persuade the customer to buy their over-priced insurance deals.

Graham