Constant need to bleed radiators

[GETDADIN]

Hi there

My dad has asked you wonderful chaps for some advice....

He has a normal (!) central heating system(what I mean is it is not the sealed combi type system like mine! ). The problem is he has to bleed his upstairs radiators on a bi weekly basis. The system is about 20 years old but the rads only about 5 years old.

Do you have any ideas why he keeps getting the air/gas and how to resolve?

Thanking you in advance.

 

[boilerbeasty]

You need to find out if its air or hydrogen. Next time he bleeds it he should hold a cup over/above the vent and then try to light the gas in the cup. If it burns with a squeak or pop then there is some hydrogen and its likely to be corrosion.
If it doesn't do anything then the chances are the system is sucking in air somewhere.

 

[GETDADIN]

That was fast - Thanks.

He did light the air and got a 4" flame!!

It is therefore likely to be corrosion, so any ideas on a cure?

 

[boilerbeasty]

You can add some inhibitor to the system, which inhibits the corrosion process. Fernox or Sentinel are popular brands. Search the forum for more information using 'inhibitor'.

Bear in mind though that if its been bad and going on for a while, the radiators may have corroded signficantly. As well as hydrogen, another product of corrosion is a sludgey deposit of various iron oxides. This gathers at the bottom of radiators, in pipes, and gets baked onto the hot parts of the boiler. Are the bottoms of the radiators cold/cooler than the tops ? This is a sign of sludge. You can clean all this out, using chemicals and by flushing with water (powerflush or do-it-yourself with a hosepipe). Then refill the system and add inhibitor.

 

[GETDADIN]

Thanks again

The entire system was acid cleaned and rads replaced as a consequence less than 5 years ago, only original equipment is the boiler. The immersion was replaced aswell.

The problem only effects upstairs rads probably for the obvious reasons. Have used Fernox. The problem has been ongoing for several years and is seemingly getting worse.

Can air enter the system by any other means and then be converted to gas? Or any other ideas?

 

[boilerbeasty]

What 'Fernox' did you use ? They make a range of products. For example if you bought restorer rather than inhibitor that would have consequences.

I guess if air is entering the system then you could have a different corrosion reaction compared to the expected anaerobic conditions which inhibitors expect to protect against.

There was a posting on here about a month ago where someone was advised to get his CH water analysed to find out what was going on. Might be worth trying to find that post and see what the outcome was.

 

[GETDADIN]

Thanks Boiler Beasty

My dad says he will investigate further and check the inhibitor quality.

Your advice much appreciated.

 

[GETDADIN]

Boiler Beasty - I think I found the post you refer to : Posted: Mon Jan 12, 2004 9:30 am Post Subject: URGENT - Hyrdrogn in NEW Central Heat Systm. by user name "Universe"

Whilst this was a fascinating (and quite comical) posting dealing with the elementary table(!), the final posting on 27 January does not give the water analysis results!! Doh!