I've been out today and at one point siphoned water from the River Wharfe which is largely derived from limestone rocks. A few miles further on I noticed that the boiler seemed very full and it took an awful long way without pumping for the level to come back down. I even stopped to blow down top and bottom of the gauge to convince myself that it was working - it was. I arrived home with the level still at the top of the sight gauge and saw that within minutes of stopping the level dropped right down to the bottom of the sight gauge. The effect of frothing from dissolved solids I suppose but I have never seen it quite so pronounced. I did wonder if the bypass was blocked but it wasn't. Shan't use that source again.

Incidentally during this I was able to see the potentail effect of Jeff's superheater supercharger when a small amount of sloppover happened with the burner on full chat going up hill - a very obvious surge of acceleration as the water went through the superheater.

Mike