Central Heating System Design Flashcards

What is the purpose of zone valves in a central heating system?

Answer: To independently control heating and hot water circuits

Zone valves (motorised valves) open and close to direct hot water flow to separate circuits such as heating and hot water, allowing independent control via separate thermostats.

Which component in a central heating system controls the time that heating comes on and off?

Answer: Programmer or timer

A programmer or timer controls when the heating and hot water circuits are active, setting on/off periods throughout the day.

What does 'commissioning' a central heating system involve?

Answer: Setting up, testing and adjusting the system to operate correctly to design specification

Commissioning includes flushing, filling, venting, pressure testing, setting controls, balancing radiators, and verifying the system meets design performance before handover.

What is the purpose of power flushing a central heating system?

Answer: To remove sludge, corrosion products and scale from the pipework and components

Power flushing uses a high-flow, low-pressure machine with chemicals to dislodge and remove accumulated sludge, rust and scale, restoring system efficiency.

What chemical is commonly added to a central heating system to prevent corrosion?

Answer: Corrosion inhibitor (e.g., Sentinel X100 or Fernox F1)

A corrosion inhibitor such as Sentinel X100 or Fernox F1 is dosed into the system water to protect metals from corrosion and prevent the formation of magnetite sludge.

What is the role of the boiler interlock in a modern central heating system?

Answer: To prevent the boiler firing when there is no demand for heat

A boiler interlock ensures the boiler only fires when there is a genuine demand for heat, preventing unnecessary cycling and improving efficiency — achieved by wiring zone valves' end switches to the boiler.