New figures show almost one in 10 gas appliances worked on by cowboy gas-fitters are unsafe.
In some parts of the North West that proportion rises to 17%.
The figures have been released by the Gas Safe Register, which lists all the licensed gas engineers.
The Register is warning of the dangers of using illegal gas-fitters and has launched a new website encouraging households to ensure they’re safe.
Carbon monoxide poisoning – which can be fatal – is one of the biggest dangers. But unsafe appliances can also explode.
A Gas Safe Register spokesperson said: “There have been a number of high profile gas incidents in the North West in the last year – placing it as one of the regions most at risk from dangerous gas appliances in the country."
The new website has an interactive map showing just how dangerous different areas are.
Crewe, Blackburn, Oldham and Manchester are named as the most dangerous areas in the region.
The Register tested 8,004 gas appliances over the past year and found, of those worked on by illegal fitters, 8 per cent were unsafe.
But that figure rose to 17 per cent in Crewe and 15 per cent in Blackburn, Oldham and Manchester.
Between 2009 and 2012, 238 cowboy gas fitters were investigated in the North West and fined a total of almost £68,000. One illegal fitter was also jailed.
The Register says there are almost 13,000 legal registered engineers working safely in the region.
Wigan was named one of the safest places in the North West, with just 2 per cent of appliances found to be unsafe.
For more information, go to www.silentkiller.co.uk.