boiler downstairs, warm water upstairs only if the tap is throttled
 

Moved into new house, boiler is fairly new - 2-3 years old. Downstairs
its possible to get extremely hot water of the kitchen tap but
upstairs, the only way to get fairly hot water is to turn the tap on
but only partially. Not enough and it seems like the water doesn't get
heated at all. Too much and its only tepid. Its the same in the
bathroom for the hot tap at the sink and the shower.

The cold water into the boiler is fed directly from mains.

Any ideas on how to solve this?

boiler downstairs, warm water upstairs only if the tap is throttled