Air in hot water pipes / system

Hi, Can anybody throw any possible solutions to a problem that has recently started on my Elddis van. (2002 Avante 505)

I have noticed the problem with the water system it is filled and the hot tap(s) not operated for period of time i.e. overnight.

When the hot tap is turned on for the first time i.e. in the morning.  Air is in the system and it tikes a few seconds for the hot water to come through from the water heater. This happens with both the kitchen sink taps and bathroom taps. The van is fitted with a Trumastore water heater.

Any ideas ?