A suitable guard should be provided whenever the appliance terminal is fitted less than 2M above the ground, above a balcony or a flat roof, the guard dimensions should be such that no part of the guard terminal is less than 50mm (2") from any part of the terminal (not including any wall plate).
Terminal Guards for Condensing Boilers are easy to install and widely specified and used by British Gas. Plastic coated (polyethylene) guards are recommended for this application.
K3 Circular Terminal Guard: 280 x 165mm (11” x 6.5”)
Please see here for the Terminal Guard Appliance list:
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