what causes corrosion in central heating systems?

Answer 1

A Lot of the corrosion is caused by electrolysis due to the number of different metals in the system.
When you bleed the radiators ,most of the time it is not air that comes out but gas given off by the electrolysis and chemical reactions taking place.
You should always put corrosion inhibitor in any water filled system.
replace it every couple of years and the system will last for years.

Answer 2

The main cause of corrosion in a wet central heating system is a process called electrolysis. The corrosion is result of a reaction between the different metals within the system, namely copper, brass and steel. The steel gets coated with residue from the copper and brass, which starts a chemical process, similar to a battery,This starts up a reaction within the system which corrodes the steel element, namely the radiators and boiler which is the sacrificial element, this in turn creates what is called iron oxide sludge, a black viscous liquid.

If this is left unchecked it not only causes radiators to leak, but reduces the efficiency of the heating system, by causing sludge to build up within the boiler and radiators, which in turn costs more in fuel bills.

This can be eliminated by adding a corrosion inhibitor and a magnetic filter to the initial installation, or by having a system that has been effected, dosed with a chemical cleanser to break down the sludge and power flushed, then install a filter and add the corrosion inhibitor. The filter should be checked and cleaned and the system water checked to see if the corrosion inhibitor needs topping up when the boilers annual service is due

Answer 3

Air getting into the system actually speeds up deterioration as oxygen is one of the essential requirements for corrosion. You’ll know if air is getting in because the radiators will need bleeding to remove the air on a frequent basis.

Where the air gets in though is another matter. It can enter through a number of routes, but the most common are through the feed and expansion cistern in the loft, the vent pipe which hangs over it or a leaking joint beside the pump.

Unfortunately, whilst it is possible to identify these, it is usually a job for a professional heating engineer to put it right.

Answer 4

The main cause of corrosion in water filled systems is dissolved Oxygen and CO2 from the air.
Water treatment to remove Oxygen is by the addition of Sodium Sulphite (Na2SO3) which combines with oxygen to form soluble Sodium Sulphate.
(2Na2SO3 + O2 = 2Na2SO4). Any good hardware store should stock the sulphite with procedure for adding it to your central heating head tank. Air will not ingress the higher pressure system but it's already in the water supplied by the water company. Regular 'Bleeding' of air from the radiators, water pump and high places of the system should help eliminate much of the problem including the CO2. The addition of other corrosion inhibitors will also help. Advice from a central heating system supplier should be sought before adding these to your system.

Answer 5

The system generates it's own small voltages ,which cause corrosive attack,because it contains more than one type of metal and the less reactive metals (like copper and brass form the uncorroded parts.Iron parts become anodic and attract all the nasties like chloride ions which dissolve them (corrosion) .Lots more is going on but it's all to do with voltages,Some coming from temperature differences from place to place .
It's possible to prevent or reduce this corrosion by using an inhibitor usually of the type used in car cooling systems:This kind of inhibitor sort of paints all the anodic areas so the nasty ions can't get at them.It is VITAL that if an inhibitor of this type is used it is kept well up to recommended strength,If it isnt all corrosion will concentrate on one small area and punch holes in the system.

Answer 6

The water is dirty and sludgy , it could actually cause u problems, in that the dirty sludge works through the system and then blocks the pump and the valve.. If you have no problems with your heating , then there isnt a major problem but could have in the future. so ,u might think about having ur system drained, flushed and then they add chemicals to clean it.. .It can work out expensive, some charge 300 to 500 pounds... Ignore maid,, they do not put in anti freeze, its a heating system , not a car,, its dark , cause its old and dirty .... and bill is also wrong ,u do not have to bleed the radiators, u only bleed if the radiator pipes are hot , but the radiator themselves are cold.

Answer 7

Not topping up with corrosion inhibitor will cause corrosion and make the system less efficient.

Answer 8

Depends on where you're seeing corrosion.

If it is a hydrocarbon fueled system and you have corrosion on the combustion side- you need to keep the gas flow hot till it exits the stack.

If it cools off then you get water and Sulfur Dioxide which forms sulfuric acid (like acid rain) which will corrode quickly.

Answer 9

Water

Answer 10

Moisture