lots of boilers now come with a permanent filling loop, they must have changed the water bylaws because you all ways had to disconnect the loop,as said all ways make sure the loop tap is off after topping up the system,if you have to do it a lot you must have a leak,check the pressure relief valve they are renown for leaking.
dennis
February 2016
NEVER leave the taps on,they should be turned off and capped off.If the pressure keeps dropping you want to start looking for a leak on the system.
anon
February 2016
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