Surely you can legally open it and just blast out the dust/cobwebs with a can of air or air pressure hose and see if that sorts it directly?
If needing setting, THEN get the gas man in?
8.5m 1990 Dennis Dart bus, 6L turbo -4 pax
- 24v system: 2x130ah 12VAGM, 40A Tracer N controller, 500W solar; 1200w & 300W puresine inverters
120L grey/fresh water, 255L Samsung fridge, LPG Califont, 5KW Chinese Diesel Heater