Re-occurring air ??

[Canton]

My bathroom radiator keeps getting a build up of air in it and is the only one in my system to do this. It's not the highest mounted radiator and is second closest to my boiler which is the highest point in the system. Boiler is an 8 year old Baxi Platinum 28HE and the 15mm system pipework is around 35 years old in a 3 bedroomed 100 year old terraced house. I am not losing any pressure at all until I release the air in the bathroom radiator which I have to do around once a week when I find that the top of the bathroom radiator is cooler. I then top the pressure back up via the filling loop if it needs it to around 1.5 bar when cold. Some weeks ago before the cold weather kicked in I ran a bottle of fernox cleaner through the system after draining and refilling leaving the cleaner in for around 5 days and running the system at high temp on the boiler control a few times. I then drained the system filled and drained it with clean water only before re-filling adding a bottle of Fernox inhibitor. Obviously I bled all of the radiators in the system after completion and did so again a few days later once the system had settled down. Do I suspect the auto air vent is not doing it's job, as apart from this the system is fine ???

 

[Canton]

Anybody ???

 

[Last Plumber]

Corrosion ?
What was water like ?
Is this the combi ?
Have you got an external expansion vessel ?

 

[jonnyswamp]

Is your 35yr old system really clean, could be producing hydrogen due to sludge being present in/near the towel rad
Once system is full, replace the cap on the AAV to rule out it isn't sucking in air

 

[Canton]

As stated boiler is a Baxi Platinum 28HE combi, water was pretty clean on the original draindown and clear as gin before adding the inhibitor. I'm stumped as to why this one particular small (600mm X 600mm) radiator keeps building up a head of air in it ??

 

[Canton]

Sorry I did'nt mention that 5 of the original 8 radiators have been replaced in the last 8 years.

 

[jonnyswamp]

Seem to be pulling in air from somewhere then if what you say is right
It's not a towel rail then, it's a 6x6 panel rad?
Towel rails seem to collect a lot more air/hydrogen than normal rads, may be it's something to do with the internal surface of them corroding/degrading quicker than a smooth standard type rad
I've never researched it so may be complete bull as far as I know
The AAV you mentioned, where on the system is it located

 

[Canton]

The AAV is located within the boiler just above the pump, as yet I have'nt looked at it as I don't really want to mess with it during this cold snap we're having just in case, the Mrs would kill me if I left her in the cold. Yes it is a panel radiator.

 

[jonnyswamp]

Forget my advice about the AAV then, don't touch anything within the boiler

 

[Dotty]

As above, please don't remove the boiler casing.