My techflow t60 shower pump negative head twin started leaking so thought I'd replace it. Bought a new one & connected up but would not start. Put old one back in but that one doesn't start either. Can feel hot pipes are hot going in and out. When turn shower on cold water trickles out. When I disconnect pump water pours out of pipes so assume not a water supply issue. Have tried google but no luck - warning I'm rubbish at DIY! Is it time to call in a plumber? Thanks.