Central Heating System Types Flashcards

In a fully pumped central heating system, how is water circulated to both the heating and hot water circuits?

Answer: By a single pump with motorised valves directing flow

A fully pumped system uses a single circulating pump combined with motorised valves (typically two 2-port or one 3-port valve) to direct flow to the heating circuit, hot water circuit, or both as required by the room thermostat and cylinder thermostat.

What is the primary disadvantage of a gravity-fed hot water circuit compared to a fully pumped system?

Answer: It has slower hot water recovery times due to lower flow rates

Gravity circulation relies on the natural convection of heated water rising, which produces much lower flow rates than a pump. This results in significantly slower hot water recovery times, meaning the cylinder takes longer to reheat after hot water has been drawn off.

Which British Standard covers the specification for forced circulation hot water central heating systems in domestic premises?

Answer: BS 5449

BS 5449 covers the specification for forced circulation hot water central heating systems for domestic premises. It sets out requirements for system design, installation, and commissioning of open-vented wet central heating systems.

In an S-plan central heating system, which valve configuration is used?

Answer: Two 2-port motorised valves

An S-plan system uses two separate 2-port motorised zone valves, one controlling the heating circuit and one controlling the hot water circuit. This allows completely independent control of each circuit, unlike the Y-plan which uses a single 3-port valve.

What is the minimum height requirement for the open vent pipe above the water level in the feed and expansion cistern?

Answer: 450mm

The open vent pipe must terminate at least 450mm above the water level in the feed and expansion cistern. This prevents water from discharging from the vent during normal pump operation and provides adequate protection against system pressurisation.

In a W-plan central heating system, what distinguishes it from an S-plan?

Answer: It uses wireless thermostatic radiator valves for zone control

A W-plan system is essentially an S-plan system but replaces conventional wired zone valves and thermostats with wireless thermostatic radiator valves for individual room temperature control. This provides more granular zone control without extensive wiring.