I've just moved into a flat I have bought (electrically heated).

There seems to be a problem with the hot water in the bathroom. When you first turn the taps on (either in the basin or tub or the shower), hot water comes out for a few seconds but then runs cold. If you turn the tap off, wait 20 seconds or so and then turn it on, you get hot water again for another few seconds.

There is no problem at all with hot water in the kitchen.

Would be very grateful for any thoughts - the flat is relatively newly built (approx. 18 months old).

Is this flat in the united states?

No its in the UK - why do you ask?

Because I think you guys pipe in you hot water a little different than us.
I pondered your question about half an hour. It is definitely a crossover with the cold side having higher pressure and probably further from the water heater.