Most probably a air lock
do you have the original installation instructions at hand they may well tell you how to get rid of it
sometimes lowering the shower head into the bath/tray helps
try turning on taps in the bath room etc may move the water depending on how its been piped
Thanks bobplum and rosebery. I thought it might be an air lock but can't find any valve to release the air so will keep trying to find on line about instructions for salamander pumps. there are only 2 pipes attached to the pump with no release valve or service valve . Thanks for the replies
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