Doubt it will catch fire. It is normal for receivers to run warm, ensure that you are keeping it in a well ventilated area. One way to look at it is that if you can feel the heat over a fairly wide area, then the heat is being dissipated. It would be warm or even hot, but not enough to burn from the outside of the case. If the heatsinks and fans were not doing what they should, then the heat would be concentrated to a very small area, would be very hot and before you know it, there would be a burnout!
I am not sure on your receivers but in some receivers, there are variable speed fans that can be set in the image, so if you look in the settings menu see if you can change the settings. You can also view the temperature of the CPU