Water should not be pumped directly from the mains, you can only pump water from a storage tank.
'I installed a return but there is no connection to the floor standing combi boiler'
So where does the return go to now ?
Why do you think you need/want a return ? the pump will only come on when the tap is opened, so should only pump the water used.
The only reason to fit a pump with a return is if you have a continuous loop, where each feed to a tap is tee'd into the main distribution pipe, used in hospitals where there's long runs and you need instant hot water, not long lags of cold water.
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