Vaillant 824E Diverter Valve

I have a 5 year old Turbomax Plus 824E (VUW 242). The diverter valve is working, but doesn't fully travel home for DHW. I don't know about the CH loop.

When I press the reset button, it works properly, and I get water at the right temperature, but if there has been a heating cycle in between, the water doesn't fully heat up, and the radiators get warm when using the hot water. Pressing the reset button (or powering off) puts everything right again.

I changed the PCB earlier this summer, and was wondering whether there is a setting to control the time to drive the diverter motor? I also don't know what the three small potentiometers do on the top left corner of the PCB. They weren't there on the old one.

Many thanks

Turn OFF the boiler.

Unscrew the diverter knurled ring and remove the motor head.

Using long nose pliers check the pin inside the valve body is free to push backwards/forwards with little force.

If not you need a new diverter.

I have stripped down the motor and valve. The valve pin moves pretty easily. I have used some silicone grease on it, and it seems to be fine.

I still don't understand why it drives fully home on a reset, but not after a CH demand. I'm sure there must be a timing to be set somewhere, as it seems to spend a lot more time doing the drive to DHW on reset than it does after CH demand.