Okay, so to update with progress…. In frustration I disconnected the Rj45 connector at the back of the Sargent control panel and reset it. And it worked! New pump seems much less powerful than previous one, despite being same rating. So, thinking was it the panel all along? I reconnected the old pump and it didn’t work.
Not sure why the panel reset may have worked but, at least I now have running water again.