It's an open forum. You can't choose not to be criticised if anyone thinks you deserve it. You can choose whether you get annoyed or not.
How can I be 100% sure it is only happening with HW? As you say, it only heats the HW up as required doesn't it, so its not constantly on. Should I run a few baths throughout the day or leave the HW running to force it on? What do you suggest?
1) Turn the boiler thermostat right up to max, and run a couple of baths. That'll exercise the boiler.
If no lockouts then
2) Turn the cylinder stat up to say 75, and the boiler stat down to 1 and the boiler will keep coming on and off trying to reach the 75 and not getting there (But be careful it'll be v hot if it does). Leave the HW on 24/7.
Neither of these will exercise all types of motorised valve but we still don't know what you have. If you'd searched only this forum you would have found:
EG or 1 x 3 port
http://content.honeywell.com/uk/homes/Catalogue/Sundial Plans/3.4 Y Plan.pdf
2 x 2 port
http://content.honeywell.com/uk/homes/Catalogue/Sundial Plans/3.2 S Plan.pdf
You must have heard of "Google"?