Central Heating System Design Flashcards

What is the recommended pH range for water in a central heating system to minimise corrosion?

Answer: 7–8.5

A slightly alkaline pH of 7–8.5 is recommended in central heating systems to minimise corrosion of ferrous and non-ferrous metals while remaining safe.

What type of pipe is commonly used for central heating pipework in modern UK domestic installations?

Answer: Copper or cross-linked polyethylene (PEX/barrier pipe)

Copper and barrier pipe (PEX or MLCP) are the most common materials for domestic central heating pipework. Barrier pipe prevents oxygen ingress which causes corrosion.

What is the function of an air vent on a radiator?

Answer: To release trapped air so the radiator fills with water and heats correctly

Manual or automatic air vents (bleed valves) on radiators release trapped air pockets that prevent the radiator from filling fully with water and heating correctly.

Under the Water Supply (Water Fittings) Regulations 1999, what is required when connecting a central heating system to the mains water supply?

Answer: An approved backflow prevention device must be installed

The Water Fittings Regulations require an approved backflow prevention device (such as a double check valve) to protect the mains supply from contamination from the heating system.

What does 'system volume' refer to when sizing an expansion vessel?

Answer: The total volume of water contained within the heating system

System volume is the total water capacity of the entire heating circuit (boiler, pipework, radiators) and is essential for correctly sizing the expansion vessel.

What is the purpose of a lockshield valve on a radiator?

Answer: To set the flow rate through the radiator during balancing and prevent unauthorised adjustment

The lockshield valve is set during commissioning to balance the system and is then locked to prevent casual adjustment, ensuring the correct flow rate is maintained.