Keith got one of the AW engineers to fix the toilet valve (£20).
Firing up the engine I followed the manual's instructions to turn the key to the "On" position for a minute before turning it to heat. But after 30 seconds the alternator warning sound stopped, all the voltage readings went horribly low, and the engine turned but didn't fire anyway. Gave it a break and then did it normally, switching straight to heat for 10 seconds. Fired up fine.
Note to self – don't forget to turn the inverter on before disconnecting the landline, if you want the breadmaker to run!
1 mile (to AW and back). 0.5 hours engine time.