Boiler Types Flashcards

What is an unvented hot water cylinder (e.g., Megaflo type)?

Answer: A pressurised hot water storage cylinder connected directly to the mains, requiring no cold water cistern

An unvented cylinder is fed directly from the mains cold water supply under pressure, storing hot water without the need for a cold water cistern, providing mains-pressure hot water.

Who is qualified to work on unvented hot water systems in the UK?

Answer: An engineer with a recognised unvented qualification (e.g., G3 certified)

Work on unvented hot water systems must be carried out by an engineer holding a recognised qualification (such as the G3 Building Regulations Part G3 unvented certificate) as it is notifiable work.

What safety devices are mandatory on an unvented hot water cylinder?

Answer: Thermostat, thermal cut-out, temperature and pressure relief valve, and expansion vessel

Unvented cylinders must have a thermostat, a separate thermal cut-out (high-limit), a temperature and pressure relief valve, and an expansion vessel to protect against catastrophic failure.

What is a heat pump in the context of domestic heating?

Answer: A device that extracts heat from air, ground or water and upgrades it to heat buildings and water

A heat pump uses refrigeration technology to extract low-grade heat from the environment (air source or ground source) and upgrades it to a useful temperature for space heating and hot water.

What Coefficient of Performance (COP) would you expect from a modern air source heat pump?

Answer: 2.5–4 (it delivers 2.5–4 kW of heat per 1 kW of electricity consumed)

A modern ASHP typically achieves a COP of 2.5–4, meaning it produces 2.5–4 units of heat energy for every unit of electrical energy consumed, making it far more efficient than direct electric heating.

What is a buffer tank and when is it used with a heat pump?

Answer: A small hot water storage vessel used to provide thermal mass, reducing short cycling of the heat pump

A buffer tank provides thermal storage so the heat pump does not short cycle. It decouples heat production from heat distribution, improving efficiency and longevity of the heat pump compressor.