Truma hot water system not working

[Rob]

Hi all, my first post. We have just purchased a 2022 Fiat Interstate One motorhome and cannot get the hot water system working.
It's a Truma Ultrarapid LPG system. Water is on, pump on, gas on, Hotwater heater switch is on. Hot tap water is cold... At external site with cowl removed, you can hear gas flow and pump.. Any ideas welcome!.