C-406: Legionella risk alarm

Q: How do I check a C-406 fault?

1. Follow site water hygiene procedure 2. Check dosing pump 3. Contact water treatment specialist Safety: Lock out fans before entry; use respiratory protection near drift.

Probable causes

Biocide dosing failure
Stagnant water

Step-by-step checks

Follow site water hygiene procedure
Check dosing pump
Contact water treatment specialist

Safety: Lock out fans before entry; use respiratory protection near drift.

Sample code — verify with the OEM manual for your exact model.

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Frequently asked questions

What does C-406 mean on a Cooling Tower?

C-406 usually indicates: Legionella risk alarm. Confirm the meaning in the manufacturer's manual for your model.

What causes C-406?

Biocide dosing failure; Stagnant water.

How do I check a C-406 fault?

Work through the numbered checks above in order, recording readings as you go. Lock out fans before entry; use respiratory protection near drift.

Other Cooling Tower codes

Disclaimer: Fault code information is guidance only. Codes and meanings vary between manufacturers and models — always follow the manufacturer's manual and your site's safety procedures, and use qualified personnel for electrical, pressure, refrigerant and combustion work.