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Is the ball valve on the inlet to the pump open?
And have you tried the Wilo instruction if airlocked of On/Off for 30secs 5 times?
Would try removing the nrv if you can
Close both lever valves on the new pump circuit.
Crack the lower compression nut on the pump.
Open the top lever valve slightly and see if water is getting through the pump and NRV.
If it does, close the top lever and open the bottom lever slightly to see if the lower section of pipe is airlocked.
Reply to the thread, titled "Drilling a hole in an immersion tank." which is posted in DIY Plumbing Advice on Plumbers Forums.
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