Servicing an Unvented Water Heater, Water Boiler, Santon, Megaflow

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Servicing Unvented Hot Water Storage Systems

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Unvented hot water storage systems have become popular in the UK since their introduction in 1985. A system of storing and supply hot water under pressure was actually invented by an Englishman in 1861. This system was then developed and became popular across the world.

Unvented hot water storage systems save space in the loft when compared to traditional systems and can supply large volumes of hot water on demand. One of the key benefits is that the hot water supply is delivered at mains pressure right across the house. However because of the possible dangers associated with water stored in a sealed vessel under pressure and at high temperature, it is important to have the system serviced once a year. This service will amongst other things test the functionality of the safely valves that operate in the event of a fault.

The EasyFlow® website and service are now live. This is a dedicated mains pressure, electric water heater service provided by Country & Town. The service is aimed at people with city centre apartments who have unvented or thermal store water heaters. Visit EasyFlow to find out more.

Click here if you would like help or advice from a Country and Town plumber


Testing the function of the safety valves	Checking the run off from the valves

We work on the following water heater systems

• Albion	• Heatrae Sadia	• Keston
• Flamco Flexcon	• Santon Premier	• Vaillant uniSTOR
• Heatline	• Santon Premier Plus	• OSO
• Ariston	• Telford	• Fabdec
• Heatrae Megaflo	• Range	• Redring Water Heating

It must be noted that an unvented cylinder should have been installed by an approved installer who would have notified the local authority of the installation. The approved installer will have installed a system recognised by an approved testing authority such as the British Board of Agrement.

When replacing parts on an unvented system it is important to always use replacement parts supplied by the manufacturer of the system.


Turing off at the mains	Venting the tank


Draining down	Draining down 2

How will your unvented system be serviced?

The servicing of an unvented hot water storage system will include the following:

• Inspecting for signs of wear or damage

• Checking to see that the correct manufacturers parts are fitted

• Testing the temperature and pressure relief valves – shown above

• Removing the line strainer and cleaning the filter

• Checking the pressure of the expansion vessel

• Setting the correct incoming water pressure


Removing the line strainer	The dirty filter on the line strainer


Cleaning the line strainer	Replacing the line strainer

Risks associated with unvented systems

Unvented water heaters are safe to use if installed and maintained correctly. They incorporate three levels of safety. Thermostats that prevent the water being heated above 60 – 65˚, high level cut-outs that operate when water reaches 80 – 85˚ because the thermostat has failed and a temperature relief valve, which operates if both of the other safety features fail and the water reaches 90 – 95˚. In addition unvented water systems also incorporate a pressure relief valve which operates at 6 – 7 bar.

If these safety features are missing or have become faulty then there is a risk that the water will overheat and pressure will build up in the water storage tank.


Checking a safety valve	Checking the pressure of the expansion vessel


Checking the incoming pressure	Setting the correct incoming pressure

Continuing maintenance

Manufactures recommend that unvented water heaters are serviced once each year and that a record of this service is kept close to the water tank. If you would like to discuss a one-off or annual service agreement for your water heater please complete the form below.