You can buy the combustion chamber. Hood and baffles for a linea and costs about 60-70 pound. Get somebody who will replace the parts it may cost a couple of hundred pound. Better than 2 grand. As Agile put the linea is a very repairable boiler.
Nath
It may not be a sludge issue. As the pump is not operated during HW. It may be a gas supply issue. Or perhaps a sensor. Has the lockout light flashed at all requiring a reset?
Nath
Get yourself a decent engineer. Get him to have one made for your fire. A call to baxi will be able to give you measurements and just take it to a sheet metal guy who will cut the holes.
Nath
Yes you use a spreader plate that sits between the joist. Insulation underneath. You will have notches to cut out at each end of the joist where it loops.
Nath