Central Heating - Serious Air Ingress Problem

Longish post - please do read to the end if you are at all experienced in this area. I'm becoming desperate!
I installed a wet central heating system & oil combi boiler from scratch last year. The only problem with it last autumn/winter was the loud noise of air in the pipes and the fact that I needed to bleed one rad every few weeks.
The air was evident from the start & I gave the system a double dose of Fernox in the hope that this would prevent corrosion while the system hopefully 'settled down' and ceased to introduce air.
Needless to say, the problem still exists and is extremely noisy (a loud, intermittent gurgling noise in the four radiators nearest the boiler) now that the CH has been fired up a couple of times this autumn.
There is no visible sign of water loss. Pressure is just over 1Bar cold (although I did temporarily raise it to nearly 2Bar in an attempt to prevent air entering). I have searched previous forum threads for similar problems and followed all relevant advice such as sealing rad valve gland nuts with wax etc.
As you will imagine, this situation is somewhat annoying and worrying from the corrosion angle. I have spoken to a CH installer and a boiler service chap. Neither could suggest what can be at fault, with the system under good pressure.
One thing I have noticed this year, but not last, is that there seems to be a noticeable amount of air getting into the domestic hot water side. I can hear it in the hot pipe when a bath is being run. There is no such noise in the cold.
Can there possibly be any connection between the CH & DHW sides? Diverter valve? There is certainly nothing visually amiss inside the combi boiler cabinet. I have even had a listen with a stethoscope to various parts of the plumbing (see, told you I was becoming desperate!)
Any advice gratefully received.
Many thanks, in advance.
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hodihouk wrote:

Mine did this for a LONG time till in desperation I put the pump on max speed, and just kept bleeding it.
Its mostly OK now, but it took months to clear it all. I ythink there must be variuous reactions on new pipework that causes new gas to arrive.
That reminds me, after 18 months I should drain it flush it and fernox it.
As far as gas in teh DHW goes, that's pretty normal. All water contains some form of dissolved gas - or indeed sodium bicarbonate that releases gas on its way to becoming limescale.
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Is your system sealed or open vented?
IF sealed, the only causes I can think of are (a) airlocks in pipes prevent all the air escaping when you fill. Partial cure: fill, run pump at full power, vent, refill.
(b) The fill water contains a lot of dissolved gas. Run hot, vent & refill while still hot.
If open, you might be over- or under-pumping. Only cure is to alter pipework, but a big dose of anti-rust might put off the evil day...
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