• LHS Plumbing Services

How to Clean the Central Heating System.

Updated: 1 day ago


Are your radiators giving off a bad smell of eggs or similar when you bleed them of air? (the removal of air via the air vent) Then this could probably be a build-up of a chemical called Hydrogen Sulphide in the water.

Hydrogen Sulphide which can build up in central heating systems not only causes a bad smell but will cause corrosion sludge and magnatite within your central heating system over time and will require removing.


A few top brands of central heating cleaner and corrosion inhibitors available are Sentinal, Fernox or Adey, any one of these would be perfect for the job, but you'll need to drain and flush out the old contaminated water from the central heating system first.


Cleaning the Central Heating System

Before you introduce a new product to the central heating system, we recommend you fully drain the heating system of water. This will remove the loose deposits and sludge suspended in the water.


Draining Down the Water in the Central Heating System

First things first, turn of the power to the boiler and controls. Allow the system to cool. If you have a vented system close the supply to the feed and expansion tank in the loft.

When you are ready to drain the system, you must find the drain cock on the pipework. This is normally found on a radiator by a doorway on the lowest part of the system. Run a hose to an outside drain and attach a clip to secure the end of the hose to the drain cock. Open the air vents at the top of the system to allow the water to drain away. Remember to close all vents once your system is empty.

Adding the Chemical System Cleaner

Check the manufacturers details on the correct amount of chemical to use in the system. The method on how to add the cleaner will determine what system you have. For an open vented central heating system, you can easily add the chemical when filling up via the feed and expansion tank.

For sealed central heating systems, the chemical comes in pressurised cartridge and is required to be connected to the air vent on a radiator via a special attachment hose. This solution is injected into the heating system.



Refilling the Central Heating System

Close the drain valve and fill the system. Remove the hose from the drain cock. With a vented system open the water supply to the tank in the loft which will allow the water to flow back into the system.

With a sealed system you need to locate the filling loop and open the valves to allow water into the system paying attention to the pressure gauge. The recommended pressure for heating systems is normally 1 bar.

You will now need to vent each radiator by opening the bleed valve to release the trapped air. Always start with the lowest level radiator and work your way to the top of the house. This reduces the chance of trapping air in the lower part of the central heating system.

Turning the Central Heating System Back On