Jan Hui
Hi, Jan here from South Coast Boilers in Newhaven. scboilers.co.uk The leak needs to be repaired, no leak = no pressure loss. The heating not working could be many reasons. Pump problem, controls not working, diverter valve faulty, diverter motor not working... Ask your gas engineer if they know how to use a 'multimeter' before employing them. Otherwise it will be "guessing" which part has failed, and you may end up with a large bill. But start with the leak repair and get some on-site advice whilst that is being repaired. If the boiler is exceptionally old or in poor condition, strongly consider a replacement with a good brand before pouring money into something that may not be worth it.
