Hot water cylinders and unvented systems

Vented or unvented?

A vented cylinder is fed from a cold water tank in the loft, and gravity does the work. It's the traditional set-up in a lot of older houses.

An unvented cylinder is fed straight from the mains, so you get mains pressure at the taps and showers and there's no tank in the loft. Because it stores hot water under pressure, it has safety devices built in: an expansion vessel, a pressure relief valve, a temperature relief valve and a tundish, the little funnel on the discharge pipe where you can see if water is escaping. These need someone who knows how they're meant to work.

Why training matters

On top of his City & Guilds, Pete has done advanced unvented pressurised cylinder training. Combined with 20 years of fault finding, that means he'll work out why the cylinder is misbehaving rather than just swapping parts until it stops.

Common problems

• No hot water, or only lukewarm water
• Water running or dripping from the tundish or discharge pipe
• Pressure dropping at the taps
• Leaks or corrosion around the cylinder
• Immersion heater faults
• An old cylinder that's reached the end of its life