Sealed System Requires Regular(ish) Bleeding

R

roberta1000

I had my CH changed to a sealed system with new boiler several months ago. I've noticed that one of the bathroom towel rails needs bled from time to time (top bar doesn't heat). When I bleed it the pressure drops by around 0.1 bar but if I leave it without bleeding the pressure stays up. So I'm puzzled - how can air get into the pressurised system whilst leaving the pressure unaffected?

This particular rail has always needed bled from time to time when I had the open header tank but I had expected it to stop when it was sealed.

On the offchance that it was hydrogen being generated I tried lighting it but no result. The system has plenty of new inhibitor in it.
 
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It's air that was originally dissolved in the water, which is collecting in its favourite place. In that case, it's just a matter of waiting until all the dissolved air comes out of solution.
 
That rad will prob need bleeding the most as i'd hazard a guess that it's the highest point of the system.
 
Thanks for the info - I'm just a bit surprised that there could be so much air dissolved in the water. No problem to just keep bleeding it, though I suppose more air will be getting in when I restore the pressure. Ah well!
 
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Next time you bleed the rad, invert a can over the vent and collect what comes out of the rad. Apply a source of ignition to the can and see if it pops. If it does then its hydrogen and another treatment will be required.
 
Next time you bleed the rad, invert a can over the vent and collect what comes out of the rad. Apply a source of ignition to the can and see if it pops. If it does then its hydrogen and another treatment will be required.

See original post.

Is it possible for air to get INTO a sealed system against the internal pressure somehow?

Is it possible that the pump can produce a negative pressure on the inlet side and draw air in from somewhere?
 
Your system runs at above atmospheric pressure ( say 1 bar) so its not possible for air to get in. It's as suggested, dissolved oxygen or as I suggested, possibly hydrogen. Have you done the test I mentioned? I suspect not.
 
If you have thermostatic valves all around and these shut down
if flow is restricted cavitation can occur and air is separated out of the water.
Any pressure forces on water can cause small amounts of cavitation.
Air then collects in the system. Or as already said an electrical fault causing slow electrolysis.
 
Out of interest, it took about 9 months for the oxygen to stop collecting in my towel warmer after the system was converted to sealed.

Now there's nothing more to bleed I have also closed the auto-vent and the pressure has been rock-steady at 1 bar.
 

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