When boiler is off and no call for heat or hot water (system cold)you can drain boiler via bleed point under boiler/pump on the right hand side, just tuck away behind return isolation valve. Or you can drain via rad drain point. F40 is high pressure, if this keeps happening after you have drained boiler and re-pressursied to 1 -1.5 bar the there may be problem with expansion vessell (May be Blocked)
gareth
December 2009
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