3 Way Diverter problem?

[madmart]

I have a customer with a Halstead Best 40 that is fine for DHW but the rads are only luke (if that) warm. I think it is the diverter valve that is causing the problem. I can hear the micro switch working when switching on but cant tell if its engaging. There is a lever on the side. Can I use this lever to turn on the heating? If I can and the heating works I will know that it is the DV or synchro valve that needs to be replaced.
Any advice will be greatly received.

 

[royalflush]

Yes push the lever all the way across. That opens port A (heating).