OK, quick update on this.
I'm pretty sure it is a single phase motor after all, with capacitor starting (thanks for the hint @ericmark ).
It appears that the connection from the neutral wire to the motor windings is open-circuit - it measures infinite resistance from that wire to every other...
OK thanks for the replies folks.
@Taylortwocities "simply dob 230v to the motor wires" - yes but which wires? There are 5 of them. I agree it may well be the timer that's faulty but I've checked all the discrete components and they're all OK (there is one IC that I haven't tested), and power...
My Vortice extractor fan has stopped working and I'm trying to determine if the problem is the timer/controller circuit or the motor. I thought the easiest place to start would be to prove whether the motor works if I wire it up directly on the bench but I can't find any documentation about how...
OK, thanks again. I'll put the new one in with an expansion vessel to be on the safe side. I think any expanding water from the old heater was just expected to drip from the pressure release valve, which presumably worked fine but isn't what seems to be recommended now.
Thanks for the reply @polesapart
So not legally required but a good idea. Probably just as well to fit an expansion vessel while I'm at it then.
Are there any legal/insurance issues if I do this as a DIY job? I'd consider myself competent but I'm certainly not a trained/certificated plumber.
I recently moved into a house that has a small 10-litre electric water heater in a "shepherd's hut" type outbuilding. The heater had corroded and was leaking so at the moment the water is turned off. I thought I'd just replace it like-for-like but having looked for a replacement I'm now not...