The R4's are prone to board failure as you have already found out.  I think the R4 was targeted at the average consumer that wanted to mine a few hours a day...  those machines really were not made to run 24/7 and when they are...  damage occurs.

L3's are great but now you are getting into some more expensive machines... not even close to an R4. 

Either way, build a dedicated room if you are going to mine in your house...  keep the dust out and most importantly...  get rid of the heat!!