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Bleed water out of a radiator to reduce the pressure. Did you close the valves after and was the boiler cold.
You may have another problem with boiler, if you set the pressure in the right zone then after 5min the pressure has gone into the red, and your certain you closed the filling valves, when was the last service ?
Reply to the thread, titled "My pressure is in the red, help!" which is posted in UK Plumbers Forums on Plumbers Forums.
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