I have a Honeywell V4073A1039 3 position divertor valve mounted in my airing cupboard controlling the heating/ HW distribution. Currently when switching on the HW and CH the radiators get hot as expected but the HW is only just warm. When switching on the HW only the water still only gets warm. The Boiler and programmer are brand new but the divertor is older. I have removed the cover and noted that the motor is warm despite the system HW and CH being off for some hours and the surrounding pipework is cold. Am I correct in assuming that the motor needs replacing or could it be more significant?

Is there a cylinder with a thermostat in your system? The stat is usually fixed onto the cylinder using a strap or band to hold it in place. If has been knocked or the setting changed you will not get the hot water you want. It could even be faulty.
Failing that the diverter valve could be defective. You can usually test the valve by a metal (latching) lever on the valve body that physically locks the valve into the 'mid' position allowing heating and hot water to operate. You can test the system this way but don't leave it locked open as you will loose control of the temperatures of the heating and hot water. Good luck!

Yes it could be something other than the motor but I think you are right yo start there.Good luck and thank you