Boiler question (pic included) - can anyone tell me what this dial is for, please?

[PunishmentRoundupWithJoon]

Can't seem to find the manual for my boiler, so am wondering if anyone can enlighten me as the to purpose of this dial (the dial on the left) Presumably, if you turn it to the right, something goes up (temperature??) - but of what? The water maybe?

I have looked online but all the images for Worcester 24i junior show a different model to mine. And all the information is technical!

I know the dial on the right is the timer, though I never use it.

Isn't the symbol underneath a radiator?

Here’s a link to your manual. It’s the central heating temperature control knob aka flow temperature.

www.worcester-bosch.co.uk/support/literature/download/8716105874

Yes, @Somanysocks , it is. But all the radiators have controls on them, apart from the living room ones. I've moved it around a bit and the living room radiators seem to be the same temperature whatever the setting of that dial. And the little round symbol has lines coming off it, like a little sun symbol.

You might have a pressure gauge if you open the cover? If its in the red open the valve for a moment

@Whatevergetsyouthroughthenight - that's brilliant - thank you!!

The instructions above say this:

CENTRAL HEATING TEMPERATURE
CONTROL

The position of this knob will determine the temperature of the
water delivered to the radiators between fully clockwise and anti-
clockwise to the mark. When the knob is turned anti-clockwise
past the position towards the ‘☀️ ’ (Summer Position), then the
appliance will operate in the HOT WATER mode only and no heat will
be delivered to the radiators.