Unvented hot

Unvented hot-water cylinders.

Below is a brief description of an unvented hot water cylinder and a couple of facts that are handy to know.

In and unvented cylinder the water is stored at about 3bar, 3 times atmospheric pressure, which, in itself, is perfectly safe. When things start getting interesting is when you start heating the water up. Harefield Plumbers can identify and service an unvented cylinder. In normal circumstances water will start to boil at 100° C. However, if the water is being stored under pressure, for example 3bar, it doesn’t in fact doesn’t even begin to think about boiling until about 132° C. Now, this doesn’t sound much of a difference, and it isn’t, until the container that the water is in cracks. If this happens the water that was a liquid at 3bar pressure immediately becomes steam at 1bar pressure. Again, this doesn’t sound like a big deal, until you realise that steam requires a container 1600 times bigger than the one it currently occupies and it needs it now! The result is a very big explosion. To stop this happening an unvented cylinder comes with an array of safety devices, if one fails, another kicks in, if this fails, yet another kicks in. A Harefield Plumber will be able to fit and inspect these safety devices. The problem is that certain devices are only safe if they have been installed properly and serviced regularly, and for this reason the homeowner needs to stay well clear of them. If you do have an unvented cylinder arrange for a G3-qualified plumber to service it every year. In the interim, keep an eye on it yourself. If you ever see water dripping running out of the pipes connected to the cylinder, call the G3-qualified plumber immediately to check it out.