I have a shower pump that has packed up and I'm trying to fix it
(before I get too smelly..).

It's a Stewart Turner Showermate 1.2 bar single and I've traced the
problem to the fact that when the reed switch is activated only the
starter coil of the motor operates, so the impeller only rotates very
slowly. I've metered both motor coils, starter and main and each has
a sensible resistance (between 50 and 100 ohms), so I don't think
they're burned out. I'm a bit lost for ideas now.. The manual is at:

http://www.stuart-turner.co.uk/PDF/18649-1-06.pdf

but it doesn't give many clues really. Anyone an expert on these..? Ta