This.
1. Gas safety checks
To ensure your tenants’ safety, all gas appliances and flues need to undergo an annual gas safety check – which should always be carried out by a suitably qualified Gas Safe registered engineer. Once this has been done, you'll be given a Landlord Gas Safety Record (LGSR) with details of all the checks that were carried out.
You can arrange for a gas safety check to be carried out any time from 10-12 months after the last completed check, without affecting the original expected expiry date. If it’s less than 10 months or more than 12 months after the last check, you’ll end up with a new deadline date 12 months from the most recent check . If you are unsure about your LGSR please contact Gas Safe Register to discuss your individual case.
Appliances owned by your tenants aren’t your direct responsibility - although it’s still up to you to ensure the safety of any connecting flues, unless they’re solely connected to the tenants’ appliance.
from this link:
https://www.gassaferegister.co.uk/gas-safety/renting-a-property/landlord-gas-responsibilities/