testing hot water cylinder stat and diverter valve

Wilchard

Boiler does not heat water in HW cylinder. I have a boiler pump & diverter valve. CH circuit is fine. Towel rails heat up when only the hot water system is switched on, but I guess that is OK as they probably are fed before the diverter. The diverter valve does spin back if I manually spin it away from its position but not far enough to open the path to the HW cylinder. I suspect the tank thermostat. I was hoping someone might suggest how to test the stat. In the absence of such advice, I am going to turn off the mains, remove said stat and see if its contacts are continuous when on and not when off and I am hoping that this is a sufficient test.:(
OK, done that & stat seems to be working fine - contact C-1 when cold, C-2 when 'hot'. but diverter valve doesn't move to HW position and, more worryingly, pump doesnt start when cyl stat calls for heat, but works fine when room stat calls? Can the diverter valve stop the pump working if faulty?

DVardysShadow

What happens when your room thermostat is satisfied?

If it is not satisfied, the valve will go back to a mid position - otherwise if it is satisfied it will go right the way back. The valve [iirc] will have a switch in it which will enable the pump.