Hot water twin impeller pump wiring to my boiler
Take a look at figure 5 in the manual. (Or any of the other figures)

None of them show you connecting the pipes in parallel across the pump. 

The cold comes in and out one side of the pump in series. The hot comes in and out the other side of pump. 

Check your plumbing in the picture against figure 5.

They are not the same.

Do you have just the hot water coming in and you are trying to use bothe sides of the pump for hot instead of hot and cold?