Inhibitor & Water Treatment Flashcards

What chemical is used to descale a central heating system or water heater?

Answer: An acidic descaler (e.g., citric acid or phosphoric acid based product) circulated through the affected component

Acidic descalers (citric acid or phosphoric acid based) dissolve calcium carbonate scale when circulated through heat exchangers or system pipework, restoring heat transfer efficiency.

Why should a central heating system be refilled with inhibitor immediately after any top-up with fresh mains water?

Answer: Fresh mains water dilutes the inhibitor concentration below effective levels, leaving the system unprotected

Each addition of fresh mains water dilutes the inhibitor; multiple top-ups can eventually reduce the concentration to ineffective levels, allowing corrosion to recommence. Inhibitor concentration must be checked and replenished.

What is 'black water' in a central heating system?

Answer: Water discoloured by suspended magnetite (iron oxide) indicating significant corrosion and lack of inhibitor treatment

Black water is heavily contaminated system water laden with magnetite from corroding ferrous components; its presence indicates the system has been operating without adequate inhibitor and requires urgent power flushing and treatment.

What standard does HHIC (Heating and Hotwater Industry Council) guidance recommend for the maximum total dissolved solids (TDS) in treated heating system water?

Answer: As specified in BS 7593 and manufacturer data — typically TDS below levels that would cause scaling or corrosion

BS 7593 and HHIC guidance provide water quality parameters for central heating systems, recommending TDS and pH values that minimise both scaling and corrosion risks throughout the system life.

What is the purpose of a deaerator or air and dirt separator in a central heating system?

Answer: To remove dissolved oxygen and micro-bubbles from system water, reducing corrosion and eliminating noise

An air and dirt separator uses a low-velocity chamber and sometimes a mesh to coalesce and release micro-bubbles of dissolved air, which carries oxygen that drives corrosion. Removing it significantly reduces magnetite formation.

What colour do inhibitor test strips typically change to indicate sufficient inhibitor concentration?

Answer: The colour varies by brand — always compare against the manufacturer's colour chart provided with the test strips

Different inhibitor brands use different chemistries and test strip colour indicators; always compare the test strip result against the manufacturer's reference chart for the specific product being tested.