I am the fire officer for the company that I work for.  Due to a faulty sensor the fire alarm system does not work.  If a call point is triggered the panel will pick it up but no sounds will go off.  

I have raised this on many occasions and get told they are having issues getting the part.  I have said that 7 months is a ridiculous amount of time.

Personally I am not happy to be working on a site with no working fire system.  What can I do about this. 

Sounds like the fire alarm system is an obsolete model and needs full replacement. If you are concerned visit the Business Fire Safety page of your local fire service website to get the contact details for the Business Fire Safety Team who can advise and if required carry out a site audit and any required enforcement action.

Your company should have implemented temporary measures during the system downtime if they wished to continue to occupy the building