The last weeks I’ve really noticed how horribly the house smells of fioul! The cuve is within an enclosed and ventilated space within the house and you smell it strongly in that room, but not normally elsewhere.
Admittedly my sense of smell and taste has changed radically recently, so could have something to do with it.
Have you had it serviced recently? Our boiler that was receiving the fuel from the tank smelt very strongly one year, but it’s behaved since having a yearly service. I’m assuming you’ve checked there’s no potential leaks, or anything left open?
I don’t mean to pry but does your sense of smell and taste changed from Covid? My wife got it 3 years ago, and it’s played havoc on her sense of smell and taste ever since. Certain things stand out very strongly to her, whereas hardly anybody else would notice.