I fitted a new radiator in the house before Xmas, which necessitated a drain down of my CH system. No problem with that; however ever since then we've been disturbed almost every morning by horrendous bubble noise coming from the en-suite bathroom towel rail.
I'm now bleeding it almost every morning and get a reasonable 'pfffft' of air our each time. I'd originally put this down to residual air in the system working its way round (my CH has always been very prone to airlocks etc when working on it). But weeks later, I don't believe that can possibly still hold true.
Where could this air be coming from? My system is sealed and fully pressurised; and I replaced the inhibitor[1] when I refilled it so this can't be corrosion. I'm a bit stumped.
Any advice appreciated.
[1] Which actually has just got me thinking on a related matter... when I poured in the bottle of Fernox, I used this same towel rail to do so, because the access is dead easy that way. However, this towel rail is on the primary circuit so it warms up with the hot water rather than the rest of the central heating. Would that imply that actually there's now no inhibitor covering the rest of the house - ie, is it isolated?