New S Plan Plus to be installed... contains 3D drawing... must be viewed :)

[doitmyself]

The house is a large 5 bed built in the 1900s

I had a large 5 bed 1905 semi, but it didn't need a 40kW boiler, only a 24kW one!

How were the boiler and rads sized?

I suggest you use Whole House Boiler Size Calculator to find out what size boiler you really need?

I agree, the radiators are oversized, but better to be over then under I say.

But you only need to size the boiler for the heat loss. Larger rads will mean that the boiler can run at a lower temperature, so it can be running in condensing mode more often.

 

[happyflyer]

AW hell what's the cost of a filter, £70 and can you guarantee that the dosing will stay in there and be replaced if it gets drained down,
better safe than sorry AW, I would like to see a better drawing before making a comment.