Old boiler.
A long time ago when I was a lad, our water was heated via. an old black kitchen range, you lit the fire with old newspapers, some kindling, then it was stoked with either coal or coke, this in turn heated water in a copper back boiler, which filled a cistern in the bathroom with hot water, the range also served an oven and subsequently heated the large kitchen, this was admittedly inefficient but it was simple and relatively cheap to run, my neighbour had a new gas condensing boiler installed, it was giving him problems, the engineer told him that it had been installed with the wrong software, he was not amused when I suggested that he took out the software and lit a fire under it, I have a quite old gas boiler that does the job, one day I will have to replace it,