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Central Heating

Exam revision materials for Plumbing Level 2&3 and ACS Gas Safety test

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Heating system water analysis

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Heating system water analysis



Circulating Pump

Heating System Controls

Minimum Requirements

Room Thermostats



Heat Emitters

Heat Loss Calculation

Radiator Sizing



Fully Pumped Hot Water and Central Heating

Gravity Hot Water and Pumped Central Heating

Gravity System

Open-vented System

Pipework Sizing

Pipework Systems

Sealed Systems

System Layout

Underfloor Heating


Boiler Sizing

Flue Types

Gas Boilers

Heat Pumps

Oil Fired Boilers


Solid Fuel Boilers

Dissolved copper test

The presence of dissolved copper in system water, at a level of 1 mg/ l or more, is indicative of corrosion problems, and is associated with excessive use of flux when installing or repairing a system, and inadequate pre-commission cleaning. Only low levels are usually recorded, as the copper in solution tends to plate out onto steel and aluminium surfaces, causing localised corrosion and wasting (at ca. 0.5 to 1.0 mg/l), and pinholing at higher readings of >1.0 mg/l.

Use of soluble copper tablet test:

Fill small test tube to the top line with sample water. Add 1 x Copper/Zinc LR tablet, crush, and mix. Wait for one minute. Hold the tube 2-3 cm from the colour scale, and compare. The number next to the best colour match is the dissolved copper level in mg/l (ppm). Reagent for ca. 50 tests supplied. Range: 0 - 5 ppm.

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Why to test?

Central heating water analysis test enables engineers to make an immediate determination of the quality of water in a heating system, enabling them to understand the causes of problems, and to select the appropriate treatment to prevent future system failures and call backs.

It will indicate whether a system has been properly pre-commission cleaned, if corrosion is either taking place, or is likely to occur, whether the system should be power flushed, and whether it has been treated with the correct level of corrosion inhibitor. If power flushing is required, analysis can confirm that all deposits and residues have been purged from a system.

Wet central heating systems must be properly cleansed, and treated with corrosion inhibitor, in order to protect them from the otherwise inevitable decay as system metals trend back to their natural state.

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pH test

pH (acidity/alkalinity)

The pH of water is an indication of how acid or alkaline it is. The scale runs from 0 to 14, with a pH of 7 being neutral. The nearer to 0 the pH value is, the more acidic, and conversely, the nearer the value is to 14, the more alkaline the water.

The corrosion rate of ferrous metals and copper becomes increasingly rapid as the pH falls below 6, and it is therefore important to ensure all residues of acidic flushing chemicals are removed after power flushing.
Aluminium heat exchangers and radiators are prone to corrosion when the pH is less than 6, or above 8.5.
Copper is adversely affected when the pH is above 9.5, as may happen when alkaline flushing chemicals or inhibitors are used, or when softened water is used to fill the system.

Use of pH paper:

Remove 5-8 cm of pH paper from the dispenser roll, and immerse in water for 30 seconds. Compare the colour with the circular chart on the side of the dispenser, and note the pH number printed next to that colour.

Supplied in 5m dispenser pack.

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Dissolved iron test

Dissolved iron 

Iron oxides, produced by corrosion in heating systems, have only limited solubility in water.

Even heavily corroded systems will rarely contain more than 5 mg/l, at which level visible red or black iron oxide particles indicate that corrosion has already occurred, and that the system should be power flushed.

Mains water often contains iron, although at levels of less than 1 mg/l. A test reading of more than 1 mg/l above the mains water indicates that corrosion is taking place (even though water drawn from the top of a radiator may be clear), and the system should be power flushed.

After power flushing, a dissolved iron level check can ensure that all flushing chemical has been removed from the system. If flushing chemical is still present, then the dissolved iron level will be higher than that for mains water.

Use of soluble iron tablet test:

  1. Fill small test tube to the top line with sample water.
  2. Add 1 x Iron LR tablet. Use the crushing rod to break the tablet into a fine powder, and mix.
  3. Wait for one minute. Hold the tube 2 - 3 cm from the colour scale, and compare. The number next to the best colour match is the dissolved iron level in mg/l (ppm).
  4. Reagent for ca. 50 tests supplied. Range: 0 - 5 ppm.
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