Constant air in rads

Hi, My house is only about 4 years old and the system has worked fine with the odd radiator bleed every now and then, but recently I have had to bleed 3 of the radiators every week as they seem to be getting loads of air from somewhere, I've checked the header tank in the loft and it is full but it's really discoloured and smells (Odd as I flushed the system last year). Another thing I have noticed but not sure if it is related is the boiler when running make a rythmic chugging noise, for want of a better description like a steam train.

Any advice please?

the header tank in the loft and it is full but it's really discoloured and smells

Click to expand...

I assume you mean the feed and expansion (F/E) tank ? This should be kept at a (low) level with the water just covering the feed pipe which is at the bottom of the tank otherwise you risk over pumping which will constantly re-oxygenate the water running around your CH making your boiler noisy and the rads fill with air, not to mention corroding your whole system. Check to see if this is happening when the C/H is running (hot water coming out of the expansion pipe into the tank). Then lower the water level as described above, get some inhibitor in there and reset the ballcock to the new lower level.

Yes I do mean teh F/E tank, it is pretty high 3/4 full which just submerges the expansion return, should I lower this then?
It has been like this though for about 9 months, so why has the air in the system got worse lately?

"air" may be hydrogen gas which is produced by corrosion. I've seen others recommend testing for this when bleeding off by using a lighted match but obvious danger of setting the curtains alight. Try capturing some in an upturned cup or tin (lighter than air) and applying a light with cup/tin well away from anything inflamable.

Did you use inhibitor after flushing?

This is too high, the level needs to be set as per previous post. It may be that your ball cock valve is leaking and has slowly topped the F/E tank up. Before you do anything, put your c/h on and look in the tank (after c/h is at max temp) to see if there is any water movement in the tank indicating that the submerged expansion pipe is feeding into the tank. If so, it also means your system is constantly being re-oxygenated = air in system, noisy boiler and lots of corrosion.
Then, set level in tank correctly, re-adjust ballcock to the new level and then check that ballcock is not dripping (which could be the cause of the tank filling and this problem coming on slowly), if so, replace ballcock valve.