Gas Safety Certificiate needed?

Maintenance

One of my tenants has recently had a new boiler fitted under the Affordable Warmth scheme and I understand that the installer will issue a Gas Safety Certificate -the tenant organised the fitting by himself - all I have had to do is give my permission for the boiler to be fitted. Does anyone know what happens in this is the case?

Also - his step son (who lives next door) has also applied for a boiler under that scheme - he has had an assessment (end Oct) but heard nothing yet - what is worrying me is that his boiler is due for its Gas Safety renewal during late December/early January - there has been lots of work on the boiler over the past couple of months, so it has been "serviced" - but am I legally obliged to have the Gas Safe check done on the current boiler or will I be ok waiting for the new boiler?

Alyson