Subwoofer

If no bass is present, in what you are playing, the subwoofer may turn itself off. Also, I've owned subwoofers that will let you select "auto-off" or just "on-off" at your discretion. "on-off" will prevent it from turning off after certain time has elapsed. Check the switches on the back.

Yeha iam afaid no switches on or off  kind of itchin for a new one any opinion on REL  or B&W room is only 230 sqf.

most subs havean auto sense switch you can turn tat switch offand set the sub to on

My SVS goes to sleep shortly after the music stops, but you can set it to stay on all in the time in the software, if you want.

Oh and you might want to turn the top end of your sub down to maybe 10-15 hz above where your main speakers start to bottom. Example, my speakers go down into the 35 hz range and my sub rolls in at 50hz, so there is only a small overlap. If done right, you shouldn’t be able to hear where the sub is.

All the best.

My Sunfire use to do that until I had Bill F rebuild it and adjust the threshold to a lower level. Cost about $260, so you might want to consider a new subwoofer. Best wishes 

If your sub falls into standby when set to cross over at 90Hz, then either you are playing bass-shy sources or the sub is malfunctioning. Sub crossover is generally set much lower, as any quality main speakers will roll off well below that point. Play something bass-heavy and it should boom unpleasantly with sub at 90Hz. If it does, that's a good sign. So then try 60Hz, and if it still booms, go down to 50Hz.

 

+1 for what Hickamore said. 
For what it’s worth, Sunfire subs are outstanding performers and punch way above their size. Would be worth the $260 to have it repaired. Seems a small price to pay… 

Ask the manufacturer.

From my experience, subs that have auto on without a hard on/off switch are pain because thats what they do: shut of in the middle of a listening session because there is no bass for an extended period: No matter how much you fiddle with settings an auto on sub almost always turns off unless you are listening to hard rock. Most of time you would have to use a high crossover setting that might not blend well with your speakers. The few auto on subs that I have owned have been my least favorite. 

Rel makes fabulous subs.  I have a pair of S/5 SHOs and in addition to adding weight and expanding the sound field, they absolutely disappear.  Subs should crossover in the 30 to 40 hz range.  They are subs, not woofers.  Much higher than that and they won't disappear and will give you a boomy sloppy bottom end.  

If I remember correctly the Sony has a gain adjustment on it. If my memory is correct I would suspect you have the gain set too high for the sub and it just isn't able to handle the signal. Again, if I am correct about the Sony having a gain adjustment on it I believe this is the same pre-pro that a friend of mine kept blowing JBL speaker surrounds out with because the gain was set too high.

Had a look at the manual for the Sunfire True Subwoofer MK IV and there is unfortunately no option to bypass the Auto on/off function. Because newer movies are usually Avengers-type they are full of low end, but if you watch dramas or listen to non-metal music, you are going to have issues. The maximum crossover on that sub is 100hz, so you are already almost maxed out.

My advice is to dump the sub and by a used Rel 5 or Rel 7.

 but i find myself always adjusting the gain up and down its a Sunfire True Subwoofer MK IV have mains center and rears set at 90 hz as the sub as well should i open the hz on the sub all the way but it gets to boomy i like tight tight bass at lowest db.

Modern media is full of extra low frequency content. Making simple remote control subwoofer adjustments whether its the gain, on/off or customizable equalization preset adjustments have become a worthwhile advantage.

Unfortunately many consumer sub bass or subwoofer manufactures are a decade behind at including these affordable features. One brand your considering has gone so far as to call these adjustments "trickery."

Beware of non comparative fanboy advise or suggestions. All the best.  

Punctuation is your friend.