I need to put in a new CH/DHW boiler. I inherited a gas combi but the
present one is conventionally flued via an 8.5m chimney (with bends).
I am reasonably happy with a combi as long as it is sufficiently
powerful - there seem to be a number which will do the job.

The current site is bad for balanced flue access and for condensate
drain/ pressure relief valve discharge pipe. I would also like to lose
the requirement for ventilation into the room (cold draughts).

There really aren't any good sites above ground from my point of view -
obviously possible ones which usually involve destroying something else
I value and/or running flue pipes across rooms.

I would like to resite the boiler to the cellar where we have good flue
access plus good access to water and gas (though it does require a hot
water pipe to be run).

However, I am struggling with the twin issues of condensate drain and
pressure relief discharge. If I understand correctly, the condensate
could be run into a syphonic trap with a pump to periodically discharge
it. Can this discharge be connected to an external cast iron soil pipe
(which in our 1906 build carries both bath(shower) outflow and foul
water from 2nd floor toilet (incidentally Cambridge's
edwardian/victorian houses have combined surface and foul water
connections to mains drainage which would not be permitted in a modern
property)).

I suspect the answer may be no. If not we may have to dig up the
concrete outside - there is a drain inspection cover a metre or so away
but no other pipes or accessible drains nearby (nearest is 6m including
3m outside and with a doorway between).

Also what about the requirement for the discharge pipe. Will this need
a different trap and pump and pipe - the type of possible flow being v
different?

As usual any help and advice most welcome.

best wishes

Nick
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Nick Holmes