We have a Triton Ivory shower. It didn't work when switched on today.
Power and water seem OK.

Looking on http://www.showerdoc.co.uk/faq/electric.html it suggests that
it might be the solenoid valve that is faulty.

Looking on http://www.showerdoc.co.uk/faq/multi-meter.html it says that
if it is a good solenoid the resistance will be 3.4K Ohms or above. I
can't get any resistance reading, suggesting that the solenoid has
failed. Am I correct in this assumption?

Is the solenoid valve an easy part to fit? (I replaced the pressure
relief device about three months ago.)