The flashing light and beeping means the glycol tank is low and needs topping up — here's how to fix it, plus what to check if it keeps happening.
What it means
The flashing/beeping is your GC4 telling you the glycol tank level has dropped below the required minimum. This is a normal, expected alert — not a fault.
How to fix it
- Top up the glycol mixture, pouring it in slowly to avoid introducing air.
- Replace the cap once topped up.
- Wait at least 5 minutes before turning the unit back on. This gives any trapped air bubbles time to escape — trapped air can stop the pump working correctly.
- Remember: you need to top up for each additional fermenter you've linked to the chiller, not just once for the unit overall.
For more detail, see page 10 of the Glycol Chiller instructions.
Still flashing after topping up? Here's what else to check
If the alarm keeps going off even after you've topped up the glycol, a few other things are worth checking:
Check for trapped air bubbles
Air bubbles can form around the sensor during filling or topping up, and this alone can trigger the alarm even when glycol levels are actually fine.
To help clear this:
- Empty the glycol tank out.
- Turn the glycol chiller off and leave it for 10 minutes.
- Refill the tank with your glycol/water mixture until the red float extends out of the filling hole.
- Wait another 10 minutes before turning the unit back on.
- Check if the alarm has stopped — if not, repeat the process once or twice more.
Check the age and condition of your glycol
Glycol density changes over time, and this can also affect the sensor reading. We recommend checking your glycol mixture every 6 months of continuous use:
- Density should sit between 1.035 and 1.042 — if it's outside this range, add water or glycol to bring it back in spec.
- If the mixture has discoloured or has visible debris, it's best to do a full replacement of the water-glycol mixture rather than just topping up.
A few things to avoid
Don't substitute water for glycol — this is a real risk, not just bad practice
The GC4 runs its tank down to -4°C to -4.5°C (23.9–24.8°F) as standard operating temperature. Glycol handles this comfortably and only starts to freeze around -15°C (5°F). Plain water, by contrast, freezes at 0°C (32°F) — well above the GC4's normal operating range.
What this means in practice: if water is used instead of glycol, it can freeze solid inside the tank and internal components during completely normal operation — not as an edge case, but as an expected outcome of running the unit at its usual set temperature. Frozen water expands, which risks cracking the plastic components inside the chiller.
This is why water should never be substituted for glycol, even temporarily while troubleshooting — beyond not replicating the air-bubble issue accurately, it's a genuine mechanical risk to the unit itself.
Don't skip the wait times
Turning the unit back on too soon, before trapped air has had a chance to clear, is one of the most common reasons the alarm reappears straight away.
Still not resolved?
If you've topped up the glycol, worked through the air bubble process, and checked the condition of your glycol mixture — and the alarm is still going off — get in touch with the Grainfather Customer Services Team for further help.