The claim comes from joint research by British Gas and homeless charity Shelter, who reckon nearly a million tenants live in unsafe homes.
The survey spoke to 4,300 private renters who claimed their landlord had not carried out a gas safety check in their home.
By law, landlords must have the gas supply and appliances at a private rental property checked every year by a qualified Gas Safe registered engineer.
The landlord should then give the tenant a copy of the safety certificate.
The Health and Safety Executive, the government agency responsible for monitoring gas safety, explains the checks identify problems like faulty boilers and leaks which can kill. Around 240 people a year die from gas fault related incidents in their homes.
Further research by British Gas and Shelter revealed that 15% of private landlords are unaware of their responsibility to keep their homes safe for tenants.
Shelter's chief executive Campbell Robb said: "It's shocking to think that in thousands of households across the country there are accidents waiting to happen because a simple safety check has not taken place. For households with children, this is an even bigger concern. Renters have a right to know that the property they are living in is safe.
"It's absolutely vital that renters are aware of the need to get an annual gas safety check. Meanwhile, landlords need to know that gas safety is not optional. Failing to get a gas safety certificate can put lives at risk."
British Gas urges landlords and tenants to look for tell-tale signs of gas problems.
These include watching for signs of staining, sooting or discolouration on, or around, gas boilers, fire or water heater.
Ventilating rooms, keeping flues clear while checking that gas flames and pilot lights burn blue are other safety tips.
