That fitter looks like it might be a gas fitter, which would make sense in the time right before electricity was available,
I wondered if it was a hot water heater for a large house, you know the maid would take hot water up for the jug & bowl set in each bedroom? The hot water jug for those sets was quite small, so the maid would take one of the large jugs of hot water. I've seen the large copper hot water heaters that sit on the stove, maybe this was the next step? GG