CENWAT Inhibitor & Water Treatment

Question 1

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

Accepted Answer

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

Answer

To act as an antifreeze

Answer

To reduce system noise

Answer

To descale the heat exchanger

Question 2

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

Accepted Answer

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

Answer

A naturally occurring scale from hard water

Answer

A type of corrosion inhibitor

Answer

A filter media used in system filters

Question 3

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

Accepted Answer

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

Answer

By adding it to the cold water cistern

Answer

Through the gas inlet

Answer

By injecting it into the boiler heat exchanger directly

Question 4

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

Accepted Answer

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

Answer

Every 5 years

Answer

Only when adding new inhibitor

Answer

Only when power flushing

Question 5

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

Accepted Answer

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

Answer

10% of system volume

Answer

As strong as possible

Answer

The concentration is irrelevant — more is always better

Question 6

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

Accepted Answer

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

Answer

The inhibitor can be added directly to the flushing chemical mix

Answer

The inhibitor is added before flushing

Answer

No preparation is needed