Unvented water heaters are becoming more popular in the United Kingdom. This because this type of water boiler provides good flow rates at taps and appliances and they take up less space than gravity systems. Unvented water heaters, unlike conventional gravity hot water systems, do not have a feed and expansion tank situated above them and as the name implies do not have a vent pipe. The vent pipe in gravity systems is open to the atmosphere and therefore prevents a build-up of pressure within the system. The fact that unvented boilers are sealed is the key difference them and open vented systems and is the reason the installation of unvented systems is carefully controlled by part G3 of the building regulations.
It should also be noted that direct unvented water heaters require the skills of a plumber qualified to work on unvented heaters and a part ‘P’ registered electrician, as their function combines both disciplines. EasyFlow have people qualified to undertake both the plumbing and the electrical work.
Albion Stainless HE
Albion TPE and Expansion Valves
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Unvented water heaters should be serviced every year
The building regulations, manufacturers and insurance companies require unvented water heaters to be serviced by a qualified plumber once every year and for a record of that service to be kept. EasyFlow operate an annual service register to make this easy for you to remember. We will send you a reminder card when your service is due, and will follow this up with a phone call to book the service appointment with a plumber. We will provide you with a service log book if you have misplaced your installation / service logbook given to you by the installer. We will also keep a record of the service history on file should you need it. Contact EasyFlow today and sign-up. EasyFlow service unvented water heaters in Manchester, Cheshire and London.
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Unvented water heaters – what are they and how do they work?
Unvented water heaters rely on the pressure and flow of the main water supply for their water pressure and water flow. If you have a poor incoming water supply then the installation of an unvented water heater will not help the situation.
In an unvented system the incoming mains water passes through a stop cock, line strainer, a pressure reduction valve and a single check valve before it enters a large water cylinder. The pressure reduction valve would typically reduce the incoming water pressure to three bars. The water could be heated directly by immersion heaters in the case of direct electric systems or indirectly by a boiler, a primary circuit and a heating coil.
As the temperature of the water increases so does it volume. The water is now trapped between the closed hot taps at the point of exit and the single check valve at point of entry. As the water expands the pressure inside the cylinder increases above its entry pressure of three bars. This expansion is taken up by an expansion vessel, or in the case of a MegaFlo an expansion bubble inside the cylinder. The expansion vessel contains a flexible membrane and is charged to a similar pressure as the static pressure of the tank.
The expansion of the water stops when the source of heat is removed. In the case of direct systems the thermostats on the immersion heaters would keep the water temperature below 65°C. Unvented water cylinders are highly insulated so should only need to be heated once per day to provide sufficient hot water for the household.
If the thermostat on the immersion heater were to fail, it would keep heating the water inside the cylinder. As a result the water would continue to expand increasing the pressure inside the cylinder. Apart from the risk of scalding the real danger occurs when the temperature passes 100°C. At this point there is a risk that the water could turn into steam in which case the steam could expand to 1600 times the volume of the water and cause an explosion. This is where the safety devices come in and prevent any risk of danger.
Replacementr Immersion Heater Thermostat
Temperature and Pressure Relief Valve
Removing Heater the Electrical Connections
The first level of defence is an overheat cut out. If the temperature passes 85°C then the overheat thermostat would activate removing any danger. This has to be manually reset. It should not be reset without a safety inspection. If this were to fail then there is a temperature and pressure relief valve which operates at 95°C. This valve opens and allows the hot water to exit the tank safely via discharge pipe and tundish to the drain. This in turn allows cold water into the tank that reduces the temperature. In addition there is an expansion valve set to 6 bars which opens if the pressure in the cylinder rises above a safe level.
How to operate an unvented water heater
Unvented water heaters are efficient and easy to use if you understand how they operate and how to set the controls. If you have just read the section above you will have an understanding of how unvented water heaters function. Here is a little information on how to get the best out of your water heater.
Replacement Control Unit Place
Temperature and Pressure Relief Valve
Installing the Replacement PRV
Most direct unvented heaters have two immersion heaters; one at the bottom of the cylinder and one halfway up. If you only have one immersion heater then it will be situated at the bottom. The immersion heater at the bottom is always the main heating element. If you have an Economy 7 or similar supply the main immersion heater will only operate during ‘economy supply hours’ typically after 12 midnight, for as the name suggests, 7 hours. There are other tariffs that function at different times. If you do not have an economy electrical supply then you will be able to operate the main immersion heater anytime of the day. The main heating element should always be fitted with a time control to avoid excessive electricity bills. The other immersion heater half way up the cylinder, if you have one, is known as the boost. You will be able to operate this at any time of the day whichever electrical tariff you have.
Expansion Valve on Manco Gladiator
Mega Flow Raining Down the Tank
Mega Flow Unvented Water Heater
How to use the boost function on an unvented water heater
In general use you should turn the boost immersion heater off and leave it off until required. All your hot water needs should be met by the lower main immersion heater. Economy 7 users will have a timed function on the supply; other users will have to set the amount of time they wish to heat the water on the time clock. Six hours between 12 – 6am should be sufficient for most people’s needs.
The boost element is used to top up the temperature of the water in the cylinder out of the above times. For example a number of people may have just taken showers and another person would like to take one; in which case the quickest way to get enough hot water for a shower is to use the upper boost immersion heater by turning it on for one hour.
Just to clarify a point. The water cylinder is not divided into compartments; it is one cylinder open inside from top to bottom. Because of its shape it stratifies the heated r information on Faultswater into layers with cold water at the bottom and hot water at the top. The hot water drawn off the top of the cylinder on its way to the taps is replaced by cold water entering at the bottom of the cylinder from the main supply. The more hot water you use the greater proportion of cold water in the cylinder. Using the boost immersion heater applies heat to the already warm section of the cylinder. As hot water rises, the water below the boost immersion heater about half the water in the cylinder, will not be heated.
In most unvented water heaters the immersion heaters used for the main heater and the boost heater are rated at 3kW. In some water heaters they are identical in other such as the Santon Premier Plus or the Heatrae Sadia MegaFlo they are different with the lower element being curved and elongated. These and other questions can be answered by your EasyFlow plumber. EasyFlow provide services in Manchester, Liverpool, Chester and Leeds.
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Makes of unvented water heater
Unvented boilers are produced by a number of manufactures such as the Telford Tempest stainless steel cylinder, Santon Premier Plus, Gledhill ElectraMate, Heatrae Sadia MegaFlo, Valliant Vantage, Albion, Manco, Kingfisher and many others. All these manufacturers produce cylinders that have been designed to operate under the increased stresses produced by high temperatures and pressures. Call an EasyFlow plumber today.
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