If you searched for this, your AirSense 11 is probably doing one of a handful of things right now: flashing "Heating system error", waking you up with a tub that is still full (or bone dry), dripping water into your mask, refusing to send data to myAir, or shutting itself off at 3 a.m. This guide goes through each of those problems in the order people actually run into them, with the checks that solve most of them at home, the workarounds users share on CPAP forums, and a clear line for when it is time to stop tinkering and call ResMed or your supplier.
A note before you start: this guide covers equipment troubleshooting. Pressure settings are prescribed, so if a problem seems related to how your therapy feels rather than how the machine works, talk to your sleep specialist or provider before changing anything.
Start here: the 60-second reset that fixes a surprising number of AirSense 11 problems
Before you dig into a specific error, do this once. It is what ResMed's own troubleshooting guide asks for first, and it clears intermittent faults more often than you would expect.
- Unplug the power cord from the machine (not just the wall) and wait two to five minutes.
- Take the water tub out, empty it, and look at the silicone seal in the lid. Make sure it is seated evenly all the way around.
- Disconnect the tubing at both ends. If you use a ClimateLineAir 11 heated tube, check the pins in the connector for water or debris.
- Check the air filter on the back. If it is grey or fuzzy, replace it.
- Reconnect the tube, slide the tub back in until it clicks, plug the power back in, and let the machine start up fully.
If the problem is gone, keep an eye on it for a few nights. If it comes back, use the sections below to narrow it down.
"Heating system error. Therapy may run without heating."
This is the single most common AirSense 11 error people ask about, and it is worth understanding what it actually means: the machine has detected a fault in the humidifier heating circuit or the heated tube and has switched heating off. Your air pressure is not affected. You can keep using the machine for therapy that night; you just will not get warm, humidified air until the fault is cleared.
What to check, in order
- Reseat the water tub. Pull it out, close the lid fully, and slide it back in until you feel and hear it click. Several users on CPAPtalk report the error disappeared after they reseated the tub properly, so this is not a throwaway step. If it does not click, see the tub-seating section below.
- Reseat the heated tube and the power supply. ResMed's troubleshooting guide for a ClimateLineAir fault is exactly this: disconnect and reconnect the tube and the power supply. If the error persists with the heated tube, try a standard (non-heated) tube for a night. If the error goes away, the heated tube is the likely culprit.
- Check the power supply. The AirSense 11 ships with a 65 W supply (24 V, 2.71 A). If you are using a third-party adapter, a travel adapter, or a supply that came with a different machine, swap back to the ResMed unit. Some retailers report that an underpowered adapter can cause the machine to disable heating. This is not confirmed by ResMed, but it is cheap to rule out. If you have lost the original, the ResMed AirSense 11 65W power supply is the exact replacement.
- Look at the heater plate. With the tub out, check the metal plate for mineral scale, dried residue, or anything that could stop the tub from sitting flat. Wipe it with a damp cloth once the machine is unplugged and cool.
- Swap the tub. One AirSense 11 owner on CPAPtalk had the error come and go for weeks, swapped hoses with no change, and finally traced it to the water tub itself; going back to a different tub ended the errors. Tubs are inexpensive, so if yours is more than six months old or has ever run dry, replace it with a new AirSense 11 standard water chamber before assuming the machine is broken.
The workaround if you need to sleep tonight
Some users report that setting Climate Control to Manual, then turning Tube Temperature and Humidity Level to Off, stops the error message from interrupting the display so they can run the machine unheated until a replacement part arrives. One CPAPtalk member who damaged his heated tube ran this way for weeks and reported his therapy numbers were unchanged. Room-temperature, dry air is less comfortable, but it is the same pressure.
When to stop and call
If you have swapped the tub and the tube and the error still appears, or if you notice a burning or melted-plastic smell, stop using the humidifier and contact your supplier. A smell after the tank ran dry has been reported by AirSense 11 users and led to warranty exchanges. The AirSense 11 carries a two-year manufacturer warranty, and suppliers typically require you to have tried a new tub and tube first, so keep those receipts.
Humidifier problems: tank still full, tank empty by 3 a.m., or no moisture at all
These three complaints sound like opposite problems, but they usually come down to the same thing: the AirSense 11 decides how much water to use based on the humidity of the air in your bedroom, not just the number you set.
Why the tank is still full in the morning
In Climate Control Auto mode, the machine targets a fixed relative humidity in the tube (ResMed's guide states 85%) and uses a built-in ambient humidity sensor. If your bedroom air is already humid, the machine barely needs to add water. One CPAPtalk user in San Francisco, where indoor humidity often sits around 75%, was convinced his humidifier was broken because the tank never went down; it was working exactly as designed. If you wake up comfortable, a full tank is not a fault.
If you wake up dry and the tank is full, check that the tub is clicked in (a poorly seated tub can leak air around the chamber instead of through it), that the heater plate is warm to the touch after a few minutes of therapy, and that Humidity Level is not set to Off. Then try switching Climate Control to Manual and raising the humidity level a step at a time.
Why the tank runs dry before morning
The AirSense 11 tub holds about 380 ml, and one user who measured it found closer to 325 ml is actually usable before the water level drops below the plate. Things that drain it faster, in rough order of impact:
- Dry bedroom air. Winter heating can drop indoor humidity to 20%. Users who measured their rooms and added a small room humidifier report the tank lasting all night again and, as a bonus, fewer wet-face mornings. If you want to test this, a $10 hygrometer will tell you where you stand.
- High humidity settings. Levels 6 to 8 use a lot of water. Try dropping one step every few nights until you find the lowest setting that still feels comfortable. One user at level 8 went to level 2 in a 70°F room and had more than half a tank left in the morning.
- A heated tube set warm. Warmer air carries more water. Lowering tube temperature a couple of degrees reduces consumption.
- High pressure and mouth leaks. More air moving through the tub means more evaporation. If you use a nasal mask or pillows and wake with a dry mouth, air may be escaping through your mouth all night; a CPAP chinstrap is the cheapest fix to try, and a full-face mask is the next step.
Running the AirSense 11 without water
You can. Set Humidity Level to Off in My Options and leave the tub in place but empty. The screen still says "Humidifier: Enabled" (the machine can still pass room-temperature air through the chamber), and that is normal. This is the setup to use on a battery, during travel, or while you wait for a replacement tub.
Related reading: Tap water or distilled water for your CPAP? and CPAP nasal dryness tips.
Water in the tube or mask (rainout), and water leaking from the humidifier
Rainout: droplets, gurgling, water hitting your face
Rainout happens when warm, humid air cools in the tube and condenses. ResMed's user guide gives two causes: the humidity level is set too high, or the tube temperature is set too low. Fix it in this order:
- Switch Climate Control to Auto if it is on Manual. Auto includes rainout protection; Manual does not.
- If you are already on Auto, or prefer Manual, raise Tube Temperature a few degrees or lower Humidity Level one step.
- Keep the machine lower than your head so any condensation drains back toward the tub instead of your mask.
- Use a fleece hose cover if your bedroom is cold at night.
- If rainout started suddenly with an older heated tube, the heating element may have failed. One user who moved from an AirSense 10 to an 11 chased rainout for weeks until replacing the heated hose fixed it.
Users who use a standard, unheated tube have far more rainout in winter. If you are fighting it every night, a heated ClimateLineAir 11 tube is the real solution; browse CPAP tubes and hoses to see what is in stock. Our full guide: CPAP rainout: how to stop water in your tubing and mask.
Water leaking from the tub, or brown water in the tub
Water on the table under your machine usually means the tub lid seal is not seated, the lid was not fully closed before inserting, or the tub is cracked. Take it out, dry everything, look at the seal under good light, and refill it with the lid held level. If it keeps leaking with a new tub, the problem is the machine's chamber cradle and it needs to be looked at under warranty.
Brown or rusty water is not normal. Users who have seen it report either mineral scale from tap water or, in a few cases, corrosion inside an older machine. Use distilled water, replace the tub, and if the discoloration continues, have your supplier inspect the machine.
The water tub will not click in, or air leaks around the chamber
This one frustrates AirSense 11 owners more than almost anything else, and it is a design quirk rather than a defect: the tub's silicone outlet is round while the machine's inlet is slightly oval, and the tub has to go in at the right angle to seal. Two techniques users swear by:
- Close the lid completely first, then tilt the tub slightly downward at the front as you slide it in. Several people say this works every time once you get the feel for it.
- Once it is in, wiggle it gently side to side and up and down. One user found this seated the round connector into the oval opening and stopped the hiss of air escaping around the chamber.
Do not force it, and do not over-close the latch. If the tub still will not seat after those two tricks, inspect the silicone outlet on the tub for tears; a new tub is the fix. A hiss of air around the chamber is worth solving because it registers as a leak and can trigger the machine to stop therapy in the night (see the next section).
The AirSense 11 turns off in the middle of the night, or turns itself on
Three separate things cause this, and they need different fixes.
- SmartStop. If your provider enabled it, the machine stops a few seconds after it detects the mask has come off. If you sleep restlessly and the mask lifts, it can stop while you are still asleep. Ask your provider to turn SmartStop off, or check whether you can toggle it under My Options.
- A large leak. The machine can stop therapy when leak is so high that it cannot hold pressure. When a CPAPtalk member complained his AirSense 11 "occasionally stops blowing," the experienced answer was to look at his leak data, and mask leak turned out to be the cause. If your machine stops without SmartStop enabled, check your myAir mask seal score, tighten or replace a worn cushion, and make sure the tub is clicked in (air escaping around the chamber counts as leak). Our guide to how often to replace mask cushions and equipment explains why a six-month-old cushion leaks.
- The machine turns itself on after the drying cycle, or restarts on its own. Two things are normal here: if SmartStart is enabled, breathing into the mask (or a draft across it) starts therapy; and ResMed's user guide states that if power is interrupted during therapy, the AirSense 11 automatically restarts when power returns. A machine that turns on by itself with SmartStart off and no power interruption is a fault; unplug it for 30 minutes and, if it repeats, contact your supplier.
The AirSense 11 will not turn on, or the screen is black
- Check both ends of the power cord and make sure the plug at the machine is fully inserted. The AirSense 11 connector has a small locking lip and can look connected when it is not.
- Try a different wall outlet; a switched outlet or a tripped GFCI is a common culprit.
- Unplug for five minutes and reconnect.
- If you use a battery or a DC converter, plug directly into wall power to rule the accessory out. Note that the AirSense 11 uses a different power supply from the AirSense 10 and from the AirCurve 11 (which uses a 90 W unit). The plugs may look alike, so check the label: the AirSense 11 needs the 65 W, 24 V supply.
- If the screen stays black on wall power with a known-good ResMed supply, the machine needs service. Call ResMed at 1-800-424-0737 or your supplier.
System fault, Error 4, and other on-screen faults
ResMed's troubleshooting guide lists three causes for a system fault Error 4, each with its own fix:
| Likely cause | What to do |
|---|---|
| The machine is too hot (direct sun, a warm room, a blanket over it) | Let it cool down completely, then disconnect and reconnect the power |
| Blocked air filter | Check the filter and replace it (AirSense 11 disposable filters) |
| Water in the air tubing | Disconnect the tube, empty it, let it dry, then disconnect and reconnect power |
For any other fault message, the official advice is a restart. If it repeats, note the exact wording and any number on the screen before you call; it shortens the support call considerably.
myAir not receiving data, "Data may not be available," and Bluetooth
A few facts clear up most of the confusion here:
- The AirSense 11 sends therapy data over a built-in cellular modem, not Wi-Fi. There is no Wi-Fi setting to configure. Bluetooth is used to pair the machine with the myAir app during setup and for some app features.
- Data uploads after therapy ends, and it can take a few hours to appear. A one-day gap is usually the server, not your machine. ResMed has had server-side outages where myAir showed "Data may not be available" and the data filled in later.
- If the signal icon in the top corner of the screen shows no bars, move the machine closer to a window or away from metal shelving. Cellular reception in a basement bedroom can be the whole problem.
If no data has arrived for several days: unplug the machine for a few minutes and reconnect it (users report this clears an intermittent software bug), confirm the serial number in the app matches the label on the bottom of the machine, and check that the app is up to date. If the signal icon is dead for days on end, the modem itself may have failed; that is a warranty repair, not something you can fix.
Want your data without myAir?
Insert an SD card (the AirSense 11 accepts a standard SD card) and read it with the free OSCAR software on a computer. It shows leak, pressure, and events in far more detail than myAir. Two tips from users: wait a few minutes after therapy ends before removing the card, and never pull it while the SD light is flashing.
Noise: louder than an AirSense 10, whistling, or gurgling
Some owners who upgraded from an AirSense 10 say the 11 is a little louder, while others find it quieter; ResMed's own figures put both around 27 dBA. If yours has gotten noticeably louder than it was, check these before assuming the motor is failing:
- Gurgling almost always means the water level is low or water has collected in the tube. Refill or empty as appropriate.
- Whistling is usually a mask leak or a cracked tube, not the machine. Run the Mask Fit test from the More menu and listen for the whistle to change as you adjust the mask.
- A dirty or wet air filter makes the blower work harder and louder. Replace it.
- A tub that is not fully seated hisses. Reseat it.
A loud, rough, or grinding blower noise that does not change with any of the above is a service issue. For a quieter setup overall, see the quietest CPAP machines on the market.
Mask leaks and the Mask Fit test
Most "machine" complaints (pressure feels wrong, machine stops, dry mouth, noise) trace back to leak. The AirSense 11 has a built-in test: from the Home screen, tap More, then Mask Fit. Put the mask on as you would to sleep, lie down in your normal position, and let the machine run the check. A poor result means adjust, not tighten; over-tightening deforms the cushion and makes leak worse. If you cannot get a good seal with a cushion that is more than a few months old, replace the cushion before replacing the mask; browse CPAP mask cushions by mask model.
If air escapes through your mouth with a nasal mask or pillows, the machine reads it as leak too. A chinstrap helps some people; others do better switching to a full-face mask. Our nasal vs. nasal pillow vs. full face mask guide covers how to choose.
Pressure feels too high, too low, or hard to exhale against
Pressure settings are prescribed and locked in the clinical menu, so an AirSense 11 that "feels" different is almost never a machine fault. Common causes and what you can adjust yourself:
- Hard to breathe out: check whether EPR is on under My Options. It lowers pressure slightly on each exhale. Read our EPR guide for what the levels do and when it can backfire.
- Pressure feels overwhelming at bedtime: use Ramp (My Options > Ramp Time) so the machine starts low and climbs over 5 to 45 minutes, or set it to Auto.
- Pressure feels weak: that is usually leak (see above), a blocked filter, or a tub not seated. Check those first.
- Bloating or swallowing air: see our aerophagia guide.
If it still feels wrong after those checks, it is a conversation with your sleep specialist about the prescribed range, not a repair. Related: Is your CPAP pressure too high?
Power supplies, batteries and travel
Because the AirSense 11 power connector carries a signal line, not every 24 V adapter works. Users who tried the AirMini DC converter report ResMed told them it is not compatible with the AirSense 11. What works:
- The ResMed 65 W AC supply for home use (a spare is worth keeping; the 65W AirSense 11 supply in non-retail packaging is the same unit at a lower price).
- The ResMed Air11 DC/DC converter for 12 V and 24 V vehicle and battery outlets.
- A battery with a built-in AC outlet, which lets you plug in the original power supply and skip the converter entirely. The Zopec Explore 4000 is built this way and lists 12 to 16 hours with the humidifier off.
Turn the humidifier and heated tube off on battery power; they are by far the biggest draw. Full details, including what happens when the power goes out mid-sleep, are in our CPAP power outage guide and our travel guide.
Firmware updates, serial number and warranty
- Updates are pushed over the cellular connection automatically, only when the machine is idle and plugged in. ResMed says to expect roughly two a year. There is no manual "check for update" button, so if a known bug fix is out and your machine has not received it, improving cellular signal is the only lever you have.
- Serial number is on the label on the underside of the machine. Have it ready for any support call.
- Warranty on the AirSense 11 is two years on the machine (one year on the water tub, 90 days on tubing). Warranty service goes through the place you bought it, so keep your receipt. Physical damage, such as a drop that knocked the heated-tube connector loose, is generally not covered, which is why it is worth trying a new tube and tub before sending a machine in.
Preventing most of these problems: a realistic maintenance schedule
| How often | What to do |
|---|---|
| Every morning | Empty the tub. Leave the lid open to dry. Wipe the mask cushion. |
| Weekly | Wash tub, tube and mask in warm water with mild soap; rinse; air dry. Rinse the reusable filter if you have one. |
| Monthly | Replace the disposable filter (sooner if it looks grey). Check the tube for pinholes and the tub seal for stiffness. |
| Every 6 months | Replace the water tub and standard tubing. Replace the heated tube yearly or when rainout appears. |
Every consumable above is on one page: AirSense 11 supplies and replacement parts. Full cleaning instructions: how to clean your CPAP machine, mask and equipment.
A 60-second tour of the AirSense 11, including the tub, tube connector and touchscreen referred to above.
Frequently asked questions
Can I keep using my AirSense 11 with the heating system error showing?
Yes. The message itself says therapy may run without heating, and users who have done so report their pressure and therapy data were unaffected. You will lose warm humidification until the fault is fixed.
Why is my AirSense 11 not using any water?
In Auto mode the machine adds only as much moisture as your room air needs. In a humid bedroom it may use very little. If you are comfortable, nothing is wrong. If you are dry, reseat the tub, confirm the heater plate gets warm, and try Manual mode with a higher humidity level.
How do I turn off the humidifier on the AirSense 11?
Go to My Options and set Humidity Level to Off. Leave the empty tub in place. If you use a heated tube, set Tube Temperature to Off as well (Climate Control must be on Manual to see both).
Does the AirSense 11 have Wi-Fi?
No. It uses a built-in cellular modem to send data to myAir and Bluetooth to pair with the app. If cellular coverage in your bedroom is poor, an SD card with OSCAR is the alternative.
Why does my AirSense 11 turn off while I am asleep?
Either SmartStop detected the mask off, or leak was high enough that the machine stopped. Check your mask seal score, replace a worn cushion, make sure the tub is clicked in, and ask your provider about disabling SmartStop.
Which power supply does the AirSense 11 use?
The 65 W ResMed supply (24 V, 2.71 A). The AirSense 10's 90 W supply and the AirCurve 11's 90 W supply are different units, even though the plugs may look similar.
How often should I replace the AirSense 11 water tub?
ResMed warranties the tub for one year; most suppliers and experienced users replace it every six months, sooner if it has run dry, leaks, or shows discoloration.
Will the AirSense 11 restart after a power outage?
Yes. ResMed's user guide states that if power is interrupted during therapy, the device automatically restarts therapy when power is restored.
Still stuck?
Most AirSense 11 problems come down to four parts: the tub, the tube, the filter and the power supply. If you have replaced the relevant one and the problem remains, it is time for warranty service. Call ResMed support at 1-800-424-0737 with your serial number and the exact error wording, or reach out to us and we will help you figure out whether it is a part or the machine. If your machine is out of warranty and repair does not make sense, a certified refurbished AirSense 11 costs far less than new, and the new AirSense 11 AutoSet with HumidAir ships same day.