First try and get a solid reason why the boiler you had failed. There is no point replacing like for like if the same issue is going to wreck the new one.
If any of the PCBs have failed and replacements are not available from your supplier there are normally people out there who can repair / replace them. Don't let any of the big energy guys force you into a replacement boiler because of that.
Aluminium heat exchangers are a con, try and get stainless if you can. The saving from the aluminium exchangers to the client is zero, it just looks good on your providers books and it's a guaranteed new boiler sooner rather then later.
Get your system flushed by a pro. Your whole water and heating system uses multiple metal types for convenience of fitting and cosmetics. Cast iron heater, aluminium heat exchange, brass fittings, copper pipe, steel radiators. Knock on effect it that all the metals react with eachother through the water and corrode creating crud on top of what's already released from the water when heated.
Said crud puts excess strain on your pumps in the boiler, external, in the shower and that can cause cavitation and a pump to fail. Pumps in boilers can generally be replaced as well.
I can't recommend a boiler on the open market as they all fell short of expectations. Currently using a Atag.