Just a few suggestions for you to try.
Try locking open both motorised valves with the manual slider control, then fire up the boiler on both heating and hot water setting. If the system runs OK, then release one motorised valve at a time to see if they do close. If they close when you release them, then they are either not wired correctly or are faulty. With the system running both heating and hot water, both valves should stay open.
You could also try turning down the speed of the pump if the valves pass the above test, as it might just be that the coil in the hot water tank is not taking the full pressure of the pump properly. Furred up pipes or a blockage or a valve not turned on fully can be the cause of this.