When I turn on the hot water I start to hear cracking or sort of expansion sounds in a couple of parts of the house. When The hot water is turned off
I still hear some noise. Is it the pipes or could it be the tankless water heater needing to be cleaned?
Probably just the pipes expanding and where they pass through joists or clamps they are tight so the pipes reposition themselves in small increments.
Then the pipes cool down and the process reverses.
The good conscientious technician or serviceperson will carry extra oils and lubricants in case the new pump did not come with oil or the oil was accidentally spilled, so the service call can be completed without an extra visit.