You should check it within 12 months of the installation date.
For more information see Regulation (36)(3)(a) of the Gas Safety (Installation & Use) Regulations 1998
Before the start of a new tenancy, you must provide a current gas safety check record. The record is valid for twelve months from the date of the check. If the new tenancy begins within this twelve-month period, this record remains current and you can copy it on to the new tenants.
If, for example, you have a gas fire in the non-residential area of a public house, the landlord’s gas safety check does not apply. Other legislation enforced by your local authority environmental health team would apply.
Duties under regulation 36 do not apply to any gas appliance or installation pipework used exclusively in a non-residential part of the premises. However, landlord’s duties for maintenance under section 4 of the Health and Safety at Work etc Act 1974 (HSW Act) may in some cases extend to such equipment, and where the part of the premises concerned is a workplace, maintenance requirements under regulation 35, together with relevant duties under the HSW Act and related regulations (eg Provision and Use of Work Equipment Regulations 1998), are applicable.
Any gas appliance or installation pipework installed in a part of premises used for non-domestic purposes but (also) serving residential accommodation (eg a central heating boiler) is regarded as a ‘relevant gas fitting’ and therefore covered by regulation 36.
If the lease is for longer than seven years and is for life, the landlord is not responsible for gas safety checks and maintenance. But if there is an implied tenancy arrangement, such as accommodation is provided as part of a job (eg vicar, publican), you should continue to carry out your duties for maintenance and gas safety checks.
If defects are found, landlords must take appropriate action to ensure gas safety.
The gas safety check record contains the results of the annual gas safety check. It should be issued on completion of the checks and not delayed even if concerns are found and not delayed until necessary remedial action has been taken. The record is a ‘living document’ and landlords should supplement it with records of any follow-up action taken (if required). This would provide a full record of the gas safety within the property.