Bright orange, corrosive, smelling water

[jumpin']

In the past year, I replaced 3 rads for a customer because of corrosion on the poorly made threads. I noticed while draining the system, the water to be bright orange with a distinctive smell. I put this down to the rads.
Anyhow, on a unrelated job recently, I just bobbed up the loft to have a look at the f&e tank and the system has filled once again with this liquid. I drained & flushed the system twice (not power flushed) & a week later the same!!
The system has zoned underfloor heating with 2 manifolds, an upper floor zoned trad radiator system, the house is heated with an oil boiler, the hot water with primaries, solar, Aga & immersion. I raised the vent and filled with Sentinel.
I'm thinking if retro fitting a Magnaclean but I'm still flummoxed as to where this water is coming from. Once this is answered, there's another question for the Aga f&e tank!!! Thank you

 

[Paulus]

If there is also an orange deposit in the tank it could well be ferrous oxide which is generated by acid reacting with iron. Can you test the water for acidity with some blue litmus paper?

This may tell you what the problem is but I haven't the foggiet idea how you would deal with it.

Sorry if this isn't much help.

 

[REDSAW]

youv'e been 'tango'ed'

 

[mountainman]

Could be just plain rusty water, is the F&E tank pumping over or is fresh oxygen getting into the system some other way?

 

[Roger Welton]

on a side note you wont get rid of the orange corrosion with a standard magnaclean as it's not magnetic, you would need the 'twin tech' version. But there must be fresh oxygenated water being pulled in somewhere to cause it in the first place (leak or pumping over?)

 

[REDSAW]

sucking air due to incorrect vent pump location.

 

[jumpin']

Cheers everyone, I've highered the vent but I think it needs to go higher. I came across something similar years back, on an ancient system with a galv. header tank. This system isn't 10 yrs old yet!
My instinct is that it's pumping over, so I'm going to address that first. I'll post back on the outcome.