Update on the hot tub. Had to fit a new pump but now it's all working fine. The real revelation is the free heat from the generator. The generator water cooling is fed through a marine heat exchanger. The other side is fed through 22mm insulated pipes about 10M to the tub although I don't think the distance would make much difference. I found a similarly sized flexible pipe in the hot tub that fed from the main circulation pump to an outlet near the base of the tub. I cut into this and fed it through the pipes to the genny. I have disconnected the electric heater in the tub. When the tub thermostat is calling for heat it runs the low speed circulation pump and, with the genny running it heats the tub at least twice as fast as the 3KW electric would.

We have set the genny timer to run from 7 to 9 pm. This leaves the tub nice and cool for daytime use and lovely and warm for the evenings. We are very chuffed and think it's the best addition to the house by far.

If anyone wants more detail then PM me.

Pete.