i have a simpson eziset 550 washer the hot water won't flow in fast?

The hot water won't flow in fast it flows in really slow and
makes a humming noise, has been like this since the day we
bought it brand new, about 5 years ago
When we bought it we were on town water but that made
no difference, now we have moved to a house which is on
tank water, that made no difference either