Went to have a look at a flat that I am thinking about buying to do up.

An elderly lady, small flat in a terrible state (shame on her
family...). She was suffering from dementia, and the estate agent knew
nothing about the place, and asked me to only spend a few minutes there
as she would get distressed otherwise. I was therefore unable to have a
really good look around.

One thing that puzzled me was the method of heating the place & the hot
water.

There was clearly heating as the place was warm, and there were warm
radiators in every room. It was advertised as having gas fired central
heating.

There was no "standard" looking radiator anywhere to be found (it is a
small place and I checked carefully). I managed to very partially open a
cupboard in one of the bedroom that was all but impossible to open
because of the mess. In it I was something that I have never seen
before. A grey rounded cylinder-type object, approx 1.2m in length and
around 30cm across, with some sort of dial/control mechanism around the
middle of it. Initially I though that it was hot water tank with
electric immersion heating, but I can only assume that this was in fact
some kind of boiler. There was also a functioning standard looking
controller/thermostat unit in the hallway.

sorry, forgot my phone in the car, so no photos.

Any idea what that could be was? I only want to reassure myself that
replacing it with a combi boiler would not require major work - i.e. new
pipes/gas supply/water/etc. It was top floor, so it is possible that
there was a tank in the attic, but this is not a major issue to remove
as I prefer a combi.