There are a few reasons why your Denon receiver has gone into protection mode. Your receiver may be protecting itself against over heating or short circuits. If your Denon receiver over heats it could get damaged beyond repair or worse start a fire. Denon has built in sensors to help prevent this calamity from happening in your life.
First make sure there is proper clearance around the receiver and nothing on top of it. You need at least six inches or clearance from the top of the unit to the top of your cabinet. If your Denon receiver is perched in an open area then this is not the case but if your receiver is in a case make sure it has proper clearance. I would take the unit out of the case and work it in open air just to see if this will fix the issue.
Another over heating issue is the sound level. Playing it too loud for too long can cause your Denon receiver to over heat. Compound that with bad ventilation and you have a recipe for protection mode.
Make sure you keep volume below 0dB. You can of course use it at that high of a level but make sure its not consistently at that level. If your setup requires it to operate at that level you will need to step up a cooling control apparatus.
Make sure there are no bare speaker wires coming incontact with each other or at the connectors. Sometimes the little strands of wire are not twisted tight enough at the connection and the stray strand will contact its neighboring connector at the unit.
Disconnect the speakers and play one at a time to try and find the speaker with the bad connection. The process of disconnecting the speakers may bring the receiver out of protection mode.
Is your Denon receiver getting supplied with the proper voltage? Are there any voltage fluctuations? These voltage disparities will trip your receiver into protection mode.
If you have a surge protector in your power strip or power supply make sure that equipment is working properly. Make sure everything is plugged in correctly.
Also make sure the actual outlet in the wall is in good shape and wired correctly. Sometimes the wires can get loose or the outlet fatigues and cant hold a plug tightly anymore.
After you have exhausted all these options you can try resetting the receiver’s microprocessor with a firmware update or a reset. Thge glitch in the firmware could be triggering the protection mode. Each unit may have a different reset procedure so you will need to check your owners manual for that.
Make sure you take note of all your settings first because resetting the receiver will bring it back to factory presets. Reset is also referred to as Reboot if you cant find the Reset option.
You may utilize the Web (Browser) Control function on Networked models to back up your settings by storing a configuration file to your hard drive before resetting rebooting your receiver.
If all else fails have your receiver looked at by a service technician. Look up the nearest Denon authorized service center.
We hope this helps. Good Day!