Inhibitor & Water Treatment Flashcards

What is the main purpose of adding a corrosion inhibitor to a central heating system?

Answer: To protect metal components from corrosion and prevent the formation of magnetite (black sludge)

Corrosion inhibitor chemicals (such as Fernox F1 or Sentinel X100) form a protective film on metal surfaces, preventing electrochemical corrosion and the formation of iron oxide sludge (magnetite).

What is magnetite and why is it harmful in a central heating system?

Answer: Black iron oxide sludge formed by corrosion that blocks radiators, damages pumps and coats boiler heat exchangers, reducing efficiency

Magnetite (Fe3O4) is black iron oxide sludge generated by corrosion of ferrous components. It settles in radiators causing cold spots, damages pump impellers and coats heat exchangers reducing efficiency.

How should inhibitor be introduced into a sealed central heating system?

Answer: Via the filling loop, through a purpose-made dosing pot, or directly through a radiator after removing the bleed valve

Inhibitor can be introduced through the filling loop using a dosing pump, through a purpose-made dosing pot on the system, or directly through a radiator bleed valve port after removing the bleed screw.

How often should the inhibitor concentration in a central heating system be checked?

Answer: Annually during a boiler service, and after any significant water loss or system work

Inhibitor concentration should be checked annually using test strips or a refractometer. After any significant water loss, top-up or system work, the inhibitor must be replenished.

What is the correct concentration range for a typical liquid corrosion inhibitor in a domestic central heating system?

Answer: As specified by the manufacturer — typically 1% of system volume (e.g., 500 ml per 50 litres)

Manufacturer instructions specify the correct dose, typically around 1% of system volume. Too little provides insufficient protection; over-dosing is wasteful and can in some cases affect water treatment components.

What must be done to the system water before adding a new dose of corrosion inhibitor after power flushing?

Answer: The system must be thoroughly flushed with clean water to remove the flushing chemicals before the inhibitor is added

After power flushing, the system must be flushed thoroughly with clean water to remove all flushing and descaling chemicals before the corrosion inhibitor is dosed, as mixing chemicals can reduce effectiveness.