A pipe from bottled gas runs across my garage at floor level and divides into two immediately before entering the cavity wall that's shared with the downstairs utility room. One branch supplies a gas hob, the other a redundant gas fire. The gas fire was u/s and never used so I had a plumber cut and cap the pipe that fed the gas fire. The pipe was cut and capped in the garage, at floor level, inches from where the pipes entered the wall. Next day I smelt rotten cabbage in the utility room which I know from experience is the indicator chemical put in propane to alert people of leaks. I assumed the pipe hadn't been capped properly, checked it out and it 100% is not leaking (capped end is vertical and faces down, placed it in a jar of water and watched intently, no bubbles plus no smell in the garage). To be 100% sure there wasn't a leak anywhere else I turned the gas off at the bottle and it's been off now for 2 days. The smell is still present although (I think) a bit better than when first detected. All I can think of is that some gas escaped into the cavity wall when the job was done and although the gas might have dissipated the chemical it carried with it lingers.
Is that likely or am I missing something obvious? And if that is the cause does anyone know how long the smell is likely to last? Or how to get rid of it?
Many thanks.