Quizzes & Puzzles2 mins ago
Central Heating
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I can't think of any circumstances under which the pressure in the radiator would be less than air pressure - so answer 2 does not apply. If the CH is gravity fed from the top tank, the pressure will be equivalent to the hot tap downstairs and i've never experienced air sucking into a tap when I turn it on. The effect of the CH pump is irrelevant.
Answer 3 does not apply because it generally isn't air that is coming out of the bleed - it is hydrogen created from the small reaction between the steel radiator and hot water, the other byproduct of which is black sludge. Any air present comes from the initial fill of the system. It collects in the top of one or more of the rads and isn't going to re-dissolve into the water.