SodaStream CO2 Leaking — Hissing Sound or Gas Smell

What Does This Error Mean?

If your SodaStream makes a continuous hissing sound or you can smell CO2 (a faint, sharp, slightly acidic smell), gas is escaping from the machine without entering the water bottle. CO2 is non-toxic but will empty your cylinder and is unpleasant at high concentrations. Resolve it promptly.

Affected Models

SodaStream Source
SodaStream Fizzi
SodaStream Crystal
SodaStream Terra
SodaStream Art

Common Causes

CO2 cylinder not sealed properly — thread not fully engaged
Damaged O-ring seal on the cylinder neck
Bottle not locked in correctly — gas escaping around bottle seal
Internal valve stuck open (rare — machine fault)
Cylinder was over-tightened and O-ring is damaged

How to Fix It

Move the machine to a ventilated area

CO2 is heavier than air and can accumulate in low-lying spaces. While not immediately dangerous at household levels, move the machine to a well-ventilated room.
Remove the CO2 cylinder

Unscrew and remove the cylinder. The hissing should stop immediately if the leak is at the cylinder connection. If hissing continues after the cylinder is removed, the machine's valve is stuck open — contact SodaStream support.
Inspect the O-ring

Look at the rubber ring at the top of the cylinder neck. A cracked, flattened, or missing O-ring will allow gas to escape. Do not use the cylinder if the O-ring is damaged.
Re-insert the cylinder carefully

If the O-ring looks intact, screw the cylinder back in slowly and straight. Avoid over-tightening which can crush the O-ring.
Check the bottle lock

If hissing occurs only when a bottle is inserted, make sure the bottle is fully snapped into the bottle holder before pressing the carbonation button.

When to Call a Professional

If removing and re-seating the cylinder stops the hissing, no professional needed. If hissing continues even without a bottle attached and with the cylinder removed, the machine's internal valve is faulty.

SodaStream Gas Leak — What to Do

A CO2 leak is wasteful (it drains your expensive cylinder rapidly) and signals that something is not sealing correctly. The fix is almost always the cylinder seal or O-ring.

Is It Safe?

Food-grade CO2 is non-toxic. At household leak levels, it is not a health risk in a ventilated space. But a prolonged leak can empty your cylinder in minutes and, in a very small sealed room, could theoretically displace enough oxygen to cause light-headedness.

If the Hissing Stops When You Remove the Cylinder

Good — the leak is at the cylinder connection, not inside the machine. Inspect the O-ring, replace if damaged, or try a different cylinder.

If the Hissing Continues After Removing the Cylinder

This indicates an internal valve fault. Contact SodaStream customer support — the machine likely needs repair or replacement.

Frequently Asked Questions

Is CO2 from a SodaStream dangerous if it leaks?

CO2 is non-toxic food-grade gas. A small leak in a normal room is harmless. However, a large sustained leak in a very small, sealed room (like a tiny pantry) could reduce oxygen levels enough to cause dizziness. Keep the area ventilated and resolve the leak promptly.

My cylinder is hissing when I first attach it but then stops. Is that normal?

A brief hiss (under one second) as the cylinder seats and the seal engages is normal. Continuous hissing that does not stop is not normal and indicates a seal problem.