i can clarify it is not a requirement to check an open flued fire with a FGA while doing a CP12, depending on MI's it will be required to confirm safety of a flueless gas fire, if there are safety concerns with a landlords cooker it could be seen as reasonable to complete the apprioriate tests using a FGA to confirm your thoughts, but not on a tenats cooker as the checks are visual only, but again if concerned then appropriate action should be taken, it isnt really about whether its a CP12 or not as they are for landlords, its about the actual task in hand which determines whether a FGA should be used