For what it’s worth, BG only fit 2 boilers. Worcester Bosch and valiant so you have a decent boiler.
They will only recommend a replacement if the appliance is RSL (reduduced service listed) which means you can’t get the parts anymore.
Problem is mate, engineers THINK they know what the problem is. If they used xsol from the start, they’d get an accurate diagnosis within 20 minutes max.
It really is a blinding bit of kit
To be fair, all our engineers have access to xsol, as long as they enter the correct GC Number and follow the procedure correctly, they ought to be able to diagnose any system or wiring fault :)