I have a solid fuel fire, from what I am told this is hooked up to my central heating system (oil)
You will need to check where/how it is connected as these will need to be blanked off.
If you are not sure where they connect, get a plumber to do that bit.
Not hard to remove the boiler yourself. Get yourself some PPE, gloves, goggles, dust mask, boots or whatever?
Turn off any electrics and drain down heating system.
Remove fireplace (brickwork)
Remove door (it lifts off) and surround (4 screws) from roomheater.
Get a club hammer and a chisel at least a foot long or a decent SDS with roto stop and start hacking at the brickwork around boiler. You will be able to see where it has been built in. It's around 30" square. Hope its been filled with loose mica as it will be easier, but probably not.
Keep digging out around boiler until you have exposed sides and top.
There will be 2 x 28mm pipes on 1 side and 2 x 22mm pipes on the other and a 5" piece of flue around a foot long, usually cast iron, off the top connecting to chimney.
If you are getting a plumber to do the pipes leave it at this.
If not and you fancy doing it yourself, cut the pipes with a junior hacksaw or quicker, batter the chisel through them where the pipes join to the boiler. (If you try slackening the nuts it won't come out unless you have it cleared completely around as you need movement and these things are not light.)
Knock the chisel in at the front edge of the flue and see if it will slide up. If it won't, just smash the cast or steel flue pipewith the hammer and chisel.
Boiler will now pull out.
Cap off old pipes at suitable position.
If you have never done anything like this before it will not be easy work and you will be at it all day.