Frank McGuire wrote:
I'm planning to instal an oil fired non-condensing combi boiler(Grant) in
the kitchen of an old cottage.
There's an existing, but disused fireplace in the kitchen and the chimney
looks good.
Is it enough just to fit a length of 4in flexible liner onto the boiler and
route it up the chimney,
with the boiler taking its air from the kitchen?

I take it I can't use a balanced flue discharging into the fireplace!

You need to line the whole stack with that stuff. Climb up and clear it
out if necessary, then drop the liner in. (I think.)