Good news. There is a reset button. worth a try.
If that doesn't work
From the photos yyou have a Truma Combi. More than one model type (2E / 4E / 6E )
This page describes them. Can you confirm a model number.
The Truma boiler (gas) heats water in your caravan without the need for electricity. The gas/electric version reduces heating time. Find out more about the Truma gas water heater.
www.truma.com
Very rare (and dangerous!) to have a circuit without a
fuse.
You need to test every
fuse in the EC328. People have been know to piggy back from a
fuse.
also worth while having a hunt around for other fuses (often in line
fuse) and if you find any make a note of where they are
The photo shows a 230v "slow blow"
fuse, readily available
Find great deals on eBay for Truma Fuse. Shop with confidence.
www.ebay.co.uk
But I doubt this is the cause of your problems