A golden rule when it comes to boilers, ovens and other devices that rely on natural gas is that if you notice a particularly strong and particularly putrid smell, you must contact a gas engineer right away as it could be the sign of an emergency.
The reason for this is that a foul smell is usually the sign of a gas leak, as the natural gas that is sold and distributed today is mixed with a foul-smelling substance caused by the compound mercaptan.
Mercaptan, also known as methanethiol, has a distinctive sulphuric smell, reminiscent of rotting cabbage or rotten eggs, and is usually so unpleasant that if it is noticed emanating from somewhere in your home, it is a sign of a serious issue that you cannot avoid.
It is added to natural gas precisely because of its strong smell; natural gas does not naturally have a smell, which means that a small gas leak could go unnoticed and lead to potentially dangerous consequences owing to its flammability.
One moment that is often described as the incident which led to mercaptan becoming legally required was 18th March 1937, when the New London School in Texas suffered from a gas leak which led to one of the biggest disasters in the history of the state.
The disaster and the resulting loss of life was blamed on the fact that natural gas is invisible and odourless, meaning that a gas leak can be allowed to build until it becomes deadly.
According to some historical accounts, the only warning sign was students complaining of headaches that could have been caused by gas inhalation.
This led to state, then national and later international legislation being introduced to ensure that mercaptan is introduced into the natural gas supply to ensure that a similar disaster is not allowed to ever happen again.