Harry Bloomfield wrote:

Regular as in a direct replacement boiler except it is of the modern and
more efficient condensing design. Retain everything else, as in - header
tank, hot water tank, radiators pipework etc. just a new boiler plus new
controls.

So that narrows your choice to a "heating only" boiler or possibly a
system boiler if you can find one that will run vented. Having said that
switching to a sealed system would not represent significant change -
you would just no longer need the header tank - and would open up a much
wide range of choice.

Since you are talking about going the combi route then gas pipe size
will be less of an issue since the maximum power demand on the boiler
(and hence gas requirement) will be lower.

--
Cheers,

John.

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