1 tank in the loft would suggest you have a primatic cylinder.
EDIT: just seen your pictures, ignore this. unless you want to know how a primatic cylinder works
you may have unseized the valve mechanically but the switch inside might still be made and thus calling for heat.
what pipes get hot? do the rads get warm?
cut a sheet of ply the same size as the boiler, then fix the new boiler to that sheet, cut a new flue hole above the existing one, then brick it up from outside.
some people call heat only boilers system boilers.
i worked with a guy for years who would call a heat only conventional boiler a system boiler, it was either a system boiler or a combi with him
it is a bit odd that they've chose to drop the pipes down right next to the radiator. Usually they're dropped in the corner and then along the top of the skirting board. Maybe there's something above that stops this?
or if the radiator is under the window the drops can be hidden behind the curtain.
plumber number 2 is right,
if your bath water drains away with no problem the little amount of condensate water will do the same, it's not boiling water, it's luke warm at best. It is acidic and that's why it's usually run in plastic because nothing destroys plastic!! (as we all should know by...
modern electric fires are surprisingly good looking nowadays, you can get a nice fire surround with it and it won't cost you an arm and a leg. Just don't expect it to heat the room though.
dead easy to fit too.
the pipe has to constantly run downhill away from the boiler so it will be difficult to run it under the floor as there probably won't be enough fall on the pipe.
condesate pumps don't run for long, 10 seconds at most and depending on how much you use your boiler they might not even go off all...