I used to do a lot of cellar pumps I used to fit two at different levels in case one failed to ventilate you need a flow of air so an extractor and an inlet that way you get a proper flow which will freshen the place up. Bob
Oil in imho it’s quick to heat up and with a heat only boiler and unvented tank you’ll have heating and all the hot water you need.If you take my advice
go for a hounds field boiler as they have a good name,and Andrew hounds field is very easy to talk to. Bob
When your soldering wet the area first and try to have a fire extinguisher handy just in case also keep checking it after for at least an hour as a spark can smoulder for a long time safety first. Bob
It’s not the square you turn it’s the blue ring I think if I remember right did on years ago I put a flat bladed screwdriver in a slot and turned it that way. Bob