GMJ
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Where was it fitted, it should be beside the burner on the hot pipe out, it should spin up every time the boiler fires to heat rads or w tank.
We have UFH and in the end it wasn't the pump squealing it was one of the zone valves. They are 'closed' until heat is demanded so we reckon the valve isn't fully shut so is whistling as the water pressure tries to get through it. It stops when that zone is on.