If ring main covered by RCD, then no need for additional breaker. If location of outside socket is reasonably protected from elements etc., the IP44 will suffice however, if in doubt, go for IP56.
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It would appear that you have a minor leak somewhere in your system and the air is collecting in the radiator highest up in your system. If you can't locate it, one way to get rid of the air would be to replace the standard bleed valve, with an automatic one which operates onlt when the internal...