I always recommend to anyone, that with any gas appliance such as water heaters, it’s best to have them checked by the official local service agent for the make of equipment you have, or a reputable independent installer/service company.
I’ve had a few people tell me recently than they’re having gas suppliers and companies just turn up, saying they’re there to check equipment. Once invited in to look, they inevitably say the system is either illegal, faulty, needs servicing, etc… Now in some cases that might be true, but for the people I know who they visited, it wasn’t.
In some cases, these visitors were from actual companies, who are simply using hard-sell or scaremongering tactics, to get people to sign up on the spot, to their service contracts. On two other occasions though, false identification and contact details were given and clearly the visitors were scammers.
My best advice to anyone, is not to let anyone into your home, unless they’ve contacted you in advance to arrange an appointment. Always ask for identification. Don’t sign up to anything and certainly don’t give bank details or credit card details.
Do have your gas appliances checked and serviced once per years, but as mentioned earlier, do so directly with the manufacturer of the equipment or via a locally recommended independent installer or service agent.
Much of this is common sense.