Gas Safety Certificate

Tenancy Deposits

Hi Can anyone please help me or advice.
One on my properties the gas safety certificate has expired the reason it has is that i cannot get in touch with the tennant to arrange to get it done, tried phoning but the phone is always switched off sent text messages no reply put notes through the letter box posted 2 letters but no response. Called at various times cant get an answer at the door.
Even entered without permission during the day to see if the tennant was still occupying the property and clearly was.
The tennant is DSS and the rent is payed direct to myself by housing benefit,
How do i stand legally and any suggestions welcome that could be done or do i leave it and if it becomes and issue state the reason it was not done is because i cant get permission of the tennant.