First I will explain what an unvented cylinder is and how it differs from a vented hot water cylinder.
Most properties in the united Kingdom were built with hot and cold water storage tanks, these tanks supplied hot and cold water to the bathrooms, and the hot water to the kitchen.
Nowadays it's becoming very popular with home owners to convert the cylinder over to an unvented cylinder.
So what is an unvented hot water cylinder?
An unvented cylinder works by using the incoming water mains to supply water to all hot outlets, whereas the vented hot water cylinder relies on a cold water storage tank to supply it with water, this is normally call low pressure.
The incoming water mains needs to have a minimum pressure of 1.5 bar for the cylinder to work correctly, the higher the incoming water pressure the better.
For an unvented cylinder to work correctly the incoming water supply pipe needs to be a minimum of 22 m, the bigger the better.
Every unvented cylinder is supplied with a pressure regulator set which is normally set to 3 bar, so if you have an incoming water pressure of 6 bar the regulator will reduce it down to 3 bar to all outlets.
The regulator is connected onto the mains water supply pipe, it has two connections one to supply the unvented hot water cylinder, the other is to connect the cold supplies, this will give an even water pressure at all outlets for both hot and cold.
If you decide to convert over to an unvented hot water cylinder, then the cold water storage tank, normally located in the loft can be removed. All the cold water outlets from the tank will need to be connected to the water mains through the regulator.
The unvented hot water cylinder still works in the same way as the vented cylinder, the water is still heated via the boiler or immersion heaters, the only difference is the water pressure.
So Do I Need an Annual Service?
The answer is simply yes, just like your gas boiler, the unvented hot water cylinder needs to be checked to make sure it is safe and working correctly.
So What Needs To Be Checked?
Every cylinder will have some form of expansion vessel, this could be internal or external and needs to be checked at least once a year.
The expansion overtime will deplete and needs to be reset.
The cylinder will also be fitted with a safety valve called a temperature and pressure relief valve, this will need to be checked to make sure that it is working correctly and doing what it is supposed to do.
An unvented hot water cylinder can only be fitted by a registered person by law, if fitted incorrectly it could become a potential bomb, just check out the videos on YouTube to see what could happen should something go wrong.
It's just as important to have the unvented cylinder serviced as it is to have your central heating boiler serviced. Always be safe and have the annual check.