Flushing the heating system with a chemical agent through a mag filter

Most people know what function mag filters perform – that they capture impurities using a magnet, thereby protecting sensitive components of the central heating system. However, few people realize that mag filters not only protect heat pumps or gas boilers, but also enable the application of cleaning agents, descalers, and corrosion inhibitors into the central heating system – or at least the majority of this type of filter has this function. In this article, you will learn how to properly apply cleaning agents through a mag filter – i.e. an impurity separator installed in the central heating system.

Flushing the central heating system using a mag filter – step by step

First of all, the heating system must be switched off and you should wait until the system has cooled down. In a heated system, higher pressures are present, and moreover cleaning agents may react with warm water. For safety reasons, the flushing of the central heating system – or more precisely the application of the cleaning agent – must be carried out on a cold system.

Isolate the mag filter using the valves and vent it

• A properly installed mag filter should have valves that allow it to be isolated. Using them, the filter should therefore be isolated – once the system has cooled down.
• Once this is done, use the air vent to vent the chamber of the mag filter.
  Regardless of the model and brand of the filter, the air vent must be located somewhere in the upper part of the device.

Drain the filter of water

• After venting, the filter must be drained of water. For this purpose, use the drain valve. In some filter models it is operated with a butterfly handle – in others with a key (as in Nordic Tec brand mag filters). The drain valve – in accordance with the laws of physics – must be located at the bottom part of the filter.
• Be careful and do not forget to close the valve after draining the water.

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Add the chemical agent, descaler or corrosion inhibitor

• The descaler, corrosion inhibitor or any other chemical agent is added through the opening prepared for this purpose at the top. In many filter models it is connected to the air vent and must be unscrewed.
• After adding the agent, the upper filling valve must be tightened again / the air vent must be reinstalled.

Refill the filter with water and vent it again

• Open the ball valve on the side from which water will flow into the valve from the system, remembering the arrow indicating the flow direction on the filter housing (important). Do not open the second valve yet, which will allow water to flow further into the system – at this stage the goal is to fill the filter with water.
• After this step, vent the filter again using the air vent valve.

Final steps of flushing the central heating system

After venting the filter again, the flushing of the central heating system is almost complete. Now make sure that the air vent is properly closed and open the valve that was blocking the flow to the rest of the central heating system – at this point both ball valves should already be open.

After completing the procedure, check for leaks. It is also advisable to wait 1–2 hours to ensure tightness before restarting the heating system. If your central heating system has a flushing mode, you may switch the system to this mode for a certain period of time.

Good practice dictates that after such procedures you should return to the boiler room or to the location of the mag filter installation and check for leaks again after 24 hours.

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