Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Disconnect the mains cable to the pump

Measurement:

Test 1:
Measure the resistance between the Live and Neutral pins (L&N).
Expect approximately 170 Ohms
Test 2:
Measure the Resistance between the Live and Earth
Expected resistance 1 MOhm or greater.
Test 3:
Measure the resistance between the Neutral and Earth
Expected resistance 1 MOhm or greater.
Test 4:
Inspect the pump for any signs of water leaks as this could also give this fault condition.