You will be pleased to know that I thought better of the Swiss cheese plan; and the gas pipes were repaired with solder joints, not sticky tape. The cylinder is a bog standard vented indirect coil.
I was maybe a tad over-ambitious in my plans. I gave myself ten days to rip out the old bathroom suite and install a new one; do the same with the cylinder; fit the pump; replace the radiator with a towel rail; strip the old tiles, wallpaper, skirtings etc, make good and tile throughout; repair a badly damaged parquet floor; repaint the woodwork; emulsion the ceiling; and install a flush light fitting. I was also going to fit a shaver socket, but after taking a good look at the wiring I backed away from that one - I am gung ho, but I am not suicidal.
Pissing around with the pump has held me up, but I reckon I am still going to get about half of it done. Though I am going to be flushing the toilet by chucking buckets of water down it for a while yet...
