Water tub is hot.

The water tub is hot if I run out of water in the morning. Is there a temperature sensor that shuts down the heat when there is no water?

No, there is no sensor to alert the machine that the water chamber is empty.
It will get hot and if hot enough long enough it stinks.

Obviously we don't want to use up all the water but sometimes we do for various reasons.
Most of the time even at maximum humidity the chamber should hold enough to last 8 hours or maybe 9 hours.

How long are you sleeping?

Some other things that will cause more water consumption.....
Big leaks will use up the water faster. So maybe you are having a lot of large leaks. Hopefully your have a machine that will report leak status to you.
Also the pressure used will affect water consumption..higher pressures will use more water.
Humidity setting obviously will affect water consumption.
Ambient room humidity will affect water consumption...like when it rains the machine may not use much water but when dry for a while it might use all the water and you never change the setting. This happened to me last night. Slept with the window open and the ambient humidity was quite high last night and I barely used any water at all. The night before I used up almost all the water and my actual hours of sleep were a bit less than last night.

It will run dry if I sleep extra on the weekend. Humidity is 3,temp is 70. If it runs dry, the tub is ruined. This would be a problem for the manufacturer to consider fixing. It could turn into a safety issue if it runs dry for hours. ResMed has no email for support, only a telephone number.

neal59 wrote:ResMed has no email for support, only a telephone number.

Yea good luck with that.

If adding more water when you sleep longer on the weekend isn't a viable option what you might do is keep a second water chamber full of water so that if you wake up you can quickly just swap out water chambers.

I use a ResMed machine...depending on ambient humidity I will use almost all the water most nights so I always have to add more water at the beginning of the night. I have seen it run dry but it must not have been for very long because it didn't stink real bad...I have forgotten to add the water and have it go dry earlier in the night and it stinks to high heaven.

The setting of 3 on a ResMed machine (the hose air temp doesn't impact water consumption) is actually a fairly low setting. If you can't get 8 hours of use with that setting without going dry I would seriously take a look at the leak data and remember that if your pressure is on the high side that will use up more water.

Now if on the weekend you are talking about longer usage but not in one solid block....just add water before you lay back down or keep a spare chamber with water in it so you can quickly swap it out.
Solid blocks of use...say 10 hours with no wake ups...could be stretching the limits there. If you sleep 6 hours and get up for some reason and go back to bed...just swap out the water chamber. I think that would be faster than trying to top off the water chamber.

Running dry isn't a common problem so ResMed isn't/hasn't ever done anything to prevent it like adding a sensor to alert the machine the chamber is empty. The majority of cpap users won't use up all the water in one sleep session so they just haven't tried to fix a problem since it doesn't impact a large number of their users.

Which ResMed model is it? The new AirSense/AirCurve model line or the prior models the S9?

FYI--running dry does NOT ruin the tank (on my Resmed machines). I have done it several times.
If water is added--with or without cleaning--it will take a few minutes to flush the funk out of the system.
Cleaning the tub shortens the time, but running the machine on cool-down helps clear the tube and mask.