Air or gas in radiators

[Tufty_b]

I cannot find any thread that matches my problem, so here goes.

I keep having to bleed the rads (I only need to bleed one rad to remove the air/gas), at least once a week.
Also the other day the boiler failed to start, and upon investigation the ball cock in the header tank was stuck in the closed position, a quick wiggle and ok for now, I have bought a replacement (high flow, as it feeds off the mains), so will fix that soon.

I have noticed that there is a small cylindrical container on the top of the boiler with a red dust cap on it. I thought that this was to auto-vent the system, however if I loosen it off then water constantly dribbles out, so it's screwed down.

Also the system frequently makes noises indicating that air/gas is present almost all the time.

I intend to flush the system with sentinel X400 in a couple of weeks and then add inhibitor X100, as I'm guessing that the gas could be hydrogen, rather than air (I don't fancy using a match to test this theory!).

Is flushing/inhibitor a good thing to do first off (to eliminate the gas) and if this doesn't work, what else can I do?

NB The system is about 10yrs old.

 

[ChrisR]

Boiler???? ?????
Replace the AAV. It must be left open.
X400 takes several weeks to work, like 6. Then you don't really clear the system much just by draining it. Do a search on flush/flushing

X100 is ok but it'll still take a while for the system to settle.

 

[Tufty_b]

ChrisR
Thanks.
I have done some surfing and found that the AAV's use a fibre washer, when dry, air escapes, when the air has gone it gets wet and it expands and blocks the hole.
Surely all I need is a new washer, or is it better just to stick a new AAV unit on.
Also how loose should the red cap be (half a turn)?

 

[felix]

How did you realize that the ball valve was stuck? Was the tank empty? If it was then you should be looking for a leak. If you are constantly topping up with new water you will constantly have to bleed out the air that comes with it.

Here's another thing to check. When the system runs, does hot water gush from the vent pipe? This is another way of getting a constant supply of new air into the water. It will also result in gradual loss of water as the hot stuff evaporates.

 

[ChrisR]

The auto air vent on your boiler does NOT work like you describe. It has a float inside and a rubber seal which closes when the water pushes the float up. Its cap should be left open at least a turn.

The wet-washer air vents are rarely used, because they're always wet.

As I said, buy a new AAV - only a couple of pounds. I also asked what your boiler is.!

Make sure that the water level on your f&e tank is set low, like 10 cm deep, so there's room for expansion of the water without it going out via the overflow.

If it overflows and takes fresh water in when cold, you'll get bad corrosion.

 

[Tufty_b]

Boiler = Potterton Prima F

I'll get a new AAV in a few days, can I just replace it or do I need to drain some water out of the system first?

Felix
I know that the ball valve was stuck because I saw it hanging horizontal in the f&e tank whilst the water level was below the outlet. I don't know how long it has been stuck, if it has only been days then probably there is a leak but if it has been stuck years then I doubt it. I might tie it up and check the water level every week.