Powerflushing

Power flushing often seems to be suggested as a cure to all sorts of unexplainable issues. Heating systems don't normally need such radical treatment however if they do it is a good idea to locate what caused the problem in the first place.

Rust consists of hydrated iron(III) oxides Fe2O3·nH2O, iron(III) oxide-hydroxide FeO(OH), Fe(OH)3. For us this means that in order to get rust we need water, oxygen, and iron. For a heating system we must have water and radiators are made of steal which contains mostly iron. The only thing left to prevent your radiators rusting and falling apart is to remove the oxygen. Water in a tap often has extra dissolved oxygen in it so when a heating system is originally filled a small amount of rusting will take place. However once this occurs the water has no more oxygen (despite it being H2O it prefers to remain like that) so the rusting stops. In a heating system the same water that was original put into should remain in it.

The problem comes when new oxygen is introduced and this can happen in the following ways:-

If the water pumps over in the header tank this bubbles the water causing oxygen to be added. This is not helped as the water is hot and readily takes up this oxygen. For example this may be caused by the pump being incorrectly set, a blockage in an air separator or the vent and feed pipes fitted into the system in the wrong place.
A poor joint that may not let water out but lets air into the heating system.
Incorrectly fitted automatic air vents.
Draining and replacing the system water on a regular basis.
A leak that is not repaired but the system water is allowed to automatically refilled.

The above have to be fixed before a power flushing as the system will quickly return to rusting once the power flush has been done if they are not.

Power flushing can be a good solution. For example it is necessary to clean a heating system when a new boiler is installed. If the boiler is installed when a current one is working a chemical can be added to the header tank prior to the work. On the day of installation the heating system is drained removing the debris. If the boiler being replaced is beyond economical repair the chemical can't be added to the system and allowed to work the only answer is to power flush the system. This is particularly important if a combination boiler is installed as these boilers often contain a water to water heat exchanger that can act as a filter.

Do you need a power flush? Look out for the following: A cold zone at the bottom of most radiators when the heating is on, probably shaped like a hump (build up of sludge in the radiator). If the cold is at the top of radiators it is air, just bleed them.