The flow rate depends on your cooling circuit, i.e. the installed coolers, the size of the hose/tube, any installed filters, the radiators and the number of angle fittings.
The sensor can only measure from 30 l/h, below that it shows 0.
This has no effect on the cooling capacity, you will only notice marginal differences at significantly higher flow rates.
There are two possibilities here, either you have an extremely restrictive loop, or a defective sensor.
The easiest way to find out is to hook the sensor into a loop with the AGB and pump.
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