Engineer attended to inspect pump being noisy when running. On arrival pump casing was found to be hot and pump was still running. The Pump Pressure Relief valve wasn¹t operating causing cavitation to the impeller and casing, heating the water up to the non-return valve with no escape.
It is important to check water flow to drain when the pump is running to keep the pump cool and reduce cavitation. Just because the cooling water isn’t required (where it’s necessary on a diesel engine as secondary cooling) it’s there for the above reasons and preventions.
The noise was coming from the distorted impeller and once the pump was drawn back the evidence became apparent.