So you'd cap off a pensioners only source of heat in the middle of winter because you are not sure of it's operating burner pressure/gas rate and the custard hasn't got the mi's, poor old dear doesn't know where she's put them! She's flustered...! And your gungho!
Please folks lets get real 🙂 By all means explain to your customer that you do not feel safe working on the appliance and cannot carry out work on the appliance until you gain more info... Put the onus on the custard or Landlord end of day! However IMHO we have no right to turn an appliance off because WE do not have the knowledge or experience to work on it! You give it a visual and inform the responsible person that you are unable to do anything further because of limited knowledge you have or available material to do your job safely!!
Well diamongas, a fair point about removing someone's sole source of heat. However, I usually come across these dfe's when they're decorative & supplementary. That's why I agree with the others who say its dodgy to work on them. Not just for your professional safety, but your clients'.