How to adjust flow rates on your Underfloor Heating System

How to adjust flow rates on your Underfloor Heating System
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[@ubershredder1989]

I have a question regarding underfloor water heating in my new appt. There is no heat coming from the floor for several days now. It was fine before. The thermostat temperature is set significantly higher than the current ambient one, and the "flame" indicator is ON, meaning that heating is on.
But there is no actual heat coming from the floor. I have attached a photo of the setup underneath the boiler. There is another interface/display which I suppose is some sort of heat sensor, however it is blank unless I turn it ON, and then it turns off after a minute.
There are also these little glass gauges, they are all at the top (zero), and only the one circled in orange wiggles a little now and then.
What seems to be the issue?
Many thanks.

[@hristobayraktarov7469]

Flow should be adjusted at the top
On the bottom- return is to be connected to control system where you can have different zones on/off and temp controls
If not then should be fully open at the return

[@beefge]

So turning the blue knob is equivalent of turning the red thingie?

[@rafiqbhatti5295]

Thank you

[@czeslawhamons2755]

what if i turn my return pipe, but nothing happening with flow clock

[@gregsmith7391]

I think those marks are US gallons per minute.

[@moi984]

Like it