Live Brown goes to L
Neutral Black goes to N.
The Hot water ON wire, green/yellow, goes to the AUX NO terminal.
The CH ON grey wire goes to the CH NO terminal.
Then you need two short wire links, both connected at one end to L. At the other end of these links..one goes to CH COM and the other to AUX COM.
If you have trouble getting 3 wires innto the L terminal you could try linking L to CH COM and then linking CH COM with the 2nd wire to AUX COM. It doesn't matter as long as both COM terminals are made Live.