We purchased a 12 unit building and put in a sprinkler system per village requirements.  Two months later it turned out that one of the units had a major bed bug infestation.  We immediately called our trusted pest control tech.  He treated the affected unit multiple times and also treated the surrounding units.  Unfortunately it has been 3 months now and our tenants still call and sporadically see bed bugs.  The pest control tech keeps going back and treating it (he probably has been there 8-10 times by now) and they still keep popping up.  We even removed a few walls to see if there were any major infestations, there were non. 

We are considering a heat treatment.  However, it's super expensive for a 12 unit building and we have the sprinkler system which I believe would get set-off in the high temperature.  

Does anyone have any advice on how to get rid of them for good?  Can we do a heat treatment with the sprinkler system and is it 100% effective?

Thanks in advance!