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HPM September 2017

52 D OME S T I C B O I L E R S & S Y S T EMS Oil-fired up about combi boilers Stuart McWhinnie, group engineering manager at Firebird, discusses the latest developments in oil-fired combi boilers Installed in over 70% of homes, the combi boiler is undoubtedly the most popular type of boiler in the UK. Providing heat and domestic hot water (DHW) without the need for a separate hot water cylinder, this type of boiler option is usually the first choice for smaller households where space is limited. Combi boilers tend to be cheaper to install than other more complex boiler systems. They can also save money on bills as they only heat the water you need. There are, however, certain considerations that should to be taken into account when selecting an oil-fired combi boiler. Size does matter Historically, size has been an issue with oil-fired combi boilers, as due to the boiler having to perform two functions (heating and DHW), the width of a standard boiler has predominantly been in excess of 600 mm. This has made them more difficult to incorporate into new and existing kitchen/utility room configurations where the standard kitchen unit width is 600mm. Instead of the twin circulating pump approach used in most oil-fired combi boilers to provide space heating and DHW functions, boilers such as the new HE Combi from Firebird utilise a single, ‘A’ rated Grundfos pump and electronic diverter valve. As space heating and DHW require different circulating conditions, the Grundfos UPS 2 pump uses integrated pressurecontrol to meet these requirements. This not only means that the size of the boiler can be reduced, but can also provide overall energy savings when compared to heating system circulators due to the energyoptimisation of the Grundfos pump. Reducing the potential for failure From an installers point of view a combi boiler may be the easiest type of boiler to install, but it is also important to have a boiler that is easy to service and maintain. Accessible pipework connections, front service access, multi-directional flue options, and a long, comprehensive warranty are all important considerations when choosing a boiler. Long-life serviceable components, together with the technological advances that reduce the potential for boiler failure, is also something that should be taken into account. Typically, oil-fired combi boilers use a number of components to create the specific central heating and hot water conditions required. One such component is the electro-mechanical flow switch, which activates the hot water function. To eliminate this risk of failure, some boilers have replaced the electro-mechanical flow switch with a temperature sensitive thermistor. When a hot water tap is opened, the thermistor will sense a change in conditions and electronically activate the boiler control circuits to run the circulating pump and divert the store water through the compact plate heat exchanger. As the temperature of the stored water starts to drop, the burner will automatically fire to service the demand. Working in conjunction with this process, the diverter valve technology provides an instant switch-over from the DHW or central heating function depending on demand. Reducing corrosion risk Corrosive debris that may be present in the primary pipework can potentially cause premature failure of the primary heat exchanger through pitting corrosion. Best practice flushing and inhibitor dosing reduces this risk, along with the recommendation of fitting a magnetic filter and regular maintenance, but the flow through the heat exchanger is also a key factor. In line with standard European practice, we have designed a complete unit which houses the secondary heat exchanger beneath the primary heat exchanger. By locating this unit at the bottom of the appliance, a wet top/bottom that promotes consistent flow through the boiler jacket is created. This type of design helps to eliminate corrosion failure and boiler inefficiency, as the potential for corrosive debris product build-up in the jacket flow paths and cavities is significantly reduced. White goods are becoming more technologically advanced, not just in terms of performance, but also in their design and aesthetic properties. With kitchen designs becoming increasingly modern and high-tech, it has never been more important for a boiler to blend in with other high-end white goods and appliances. In off-gas areas of the UK, oil does provide a cheaper heating option than Liquefied Petroleum Gas, but it is still important that the latest technologies are adopted by manufactures of oil-fired boilers to maintain their competitive edge. These technologies, when coupled with ease of installation, service and maintenance, make an oil-fired boiler the number one choice for installers and homeowners alike. www.hpmmag.com September 2017 enquiry number 129 “A combi boiler may be the easiest type of boiler to install, but it is also important to have a boiler it is easy to service and maintain” Along with advanced technology options, the look of the product and how it blends into the rest of its surroundings is equally important to homeowners The combi boiler is installed in over 70% of homes


HPM September 2017
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