LeafsReefer
Active Member
Does anyone know what a solid red light on the Osmolator 3 means? I even turned off and cleaned it and left it out of the tank, but when I power on it doesn't even flash, just goes straight to a solid red light.
Tunze Osmolator 3 solid red light
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LeafsReefer
Active Member
Correction, it does flash 3 white lights, a quick blue light and then solid red.
It a really frustrating that this is my second sensor go. The first Tunze didn't respond to me and I had to buy a new one.
It a really frustrating that this is my second sensor go. The first Tunze didn't respond to me and I had to buy a new one.
SaltyMcBubble
New Member
Solid red = safety sensor triggered (water too high / overfill protection). 
On the Tunze Osmolator 3 (3154), the status LED codes are:
• White flashing — Initialization/calibration of the thermal safety sensor (and indicates pump performance mode: slow = standard, fast = boost). This can take from ~30 seconds up to a few minutes.
• Blue — Primary optical sensor detects low water → dosing/pump running.
• Solid red — Independent thermal safety sensor activated (water has reached/touched it). Pump is forced off. 
• (For reference: flashing red = 10-minute safety timer; green = water level OK; orange variants = dry-run or blocked pump; magenta = internal/pump connection error.)
Your sequence (a few white flashes → brief blue → solid red) is typical of power-up/init, the optic sensor briefly seeing low water and starting to dose, then the higher safety sensor immediately (or very quickly) detecting water and shutting everything down.
What to check / do
1. Confirm the actual water level relative to the sensor. The main optical cone controls the normal level; the small safety “nipple” higher up is the emergency cutoff. Water should not be touching the safety sensor in normal operation.
2. Make sure the sensor is mounted level/plumb with the cable exiting straight up from the top center. Angles or mounting issues can cause false triggers.
3. Dry the safety sensor area thoroughly if it got wet. Strong drafts, very cold air, or certain nearby lights (especially UV sterilizers or grow/refugium lights that emit IR or create interference) can also affect the thermal or optical sensors.
4. Power-cycle the unit (unplug for a bit, ensure safety is dry and water level is correct relative to the main sensor, then plug back in). It should go through white flashing init again and then settle to green (or blue if it needs to top off a little).
If it keeps going solid red after the safety is dry and the level looks right, it is often a sensor positioning, mounting, or (less commonly) hardware issue—contact Tunze support (Roger at Tunze USA is very responsive on these). This matches reports from other users with the same solid-red behavior.
LAX Noob Reef
Well-Known Member
Either water too high, or the sensor part is damage. My sensor had weirdly cracked, so had to do a warranty.
DmitryB
Well-Known Member
Tangentially related but I wish the sensor would have a line on the lysine cover showing exactly where the sensor is inside so you know the correct placement. I'm always just estimating.
LeafsReefer
Active Member
Thanks everyone for the advice. Unfortunately it looks like a HW issue since I left it dry at started it out of the tank and it still went red.
Do you know how to contact Roger at Tunze USA?
Do you know how to contact Roger at Tunze USA?
I usually set the water level to where I want it then just put the sensor in and slide it up or down untill the light turns green and add the outside magnet.
Are you in Ontario California or Ontario Canada, if you are in the US I can help, DM me. For Canada, you need to contact Xenia North America.
LeafsReefer
Active Member
I'm in Canada
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