The amplifier protection circuit is kicking in. There are a number of possible reasons. One is that you have a problem with your speakers or speaker wiring. Carefully inspect your speakers for any changes, and examine the wires looking for shorts or opens. If it isn't a speaker problem, then something in the amp is triggering the protection event. It could be thermal (something getting too hot). That could be due to bad air circulation, dust, or an electronic component failure. A second event would be DC voltage on the speaker outputs. This could be due to a bad capacitor, leaky semiconductor, or the bias adjustment (if it has one) that needs to be reset. A third event would be high current draw. That most likely would be due to a semiconductor that is about to blow. You should have this checked out. If you keep doing your override, you may blow out something that wouldn't otherwise fail. Or you can wait for something to blow, and then it would be much easier to find the root cause (just look for the smoke).
I own this receiver, and 18db is damn loud. Granted - your room might be significantly larger than mine with your speakers spread much further apart, or your speakers might be much less efficient than mine (this means that they want more power than the receiver can dish out - I have whatever speakers came with the "YAMAHA Home Theater in a Box" [the model that came with the HTR-5830]), but I'm pretty sure that the receiver doesn't get any louder (or at least not much). My suggestion is to turn down the volume to about -20db and work up from there after the movie has started. It might be easier to test the volume using music. The negative sign is deceiving - I rarely bring mine up to 0db. Also check the resistance - there's a red switch on the back of the receiver that switches between 6 and 8 ohms - make sure that it matches your speakers' resistance. If turning down the volume doesn't work, then post the problem again. Hope This Helps.
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