Pressure Gauge

If the pressure indicator system on a boiler is too high how can you reduce it?

The system pressure gauge Worcester bosch boiler on my (green star junior 28i) rose too high. The small bar is in the red zone 3. How can I reduce the area green? I need to bleed a radiator or is there a procedure similar to when the pressure is too low (you use the key?)

you must either turn the water temperature down to the boiler must be between (140-180) if temp isn't too high, while the drainage to system. Only do so when water is cooled. there should be several places to do this in the basement.

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