Frequently Asked Questions

Frequently Asked Questions


  • You can read the pressure shown by the manometer on the appliance. In the case of appliances which do not have an analogue manometer you see the current pressure by selecting «pressure» from the appliance menu. The minimum pressure when the system is cold is 1 bar, but the optimum pressure is 1-1.5 bar. In large flats (with systems with a large water volume) it is good not to let the pressure get too high, because as the pressure rises the available expansion vessel volume is reduced. When the combi boiler operates and gets warm, the pressure will increase. The maximum operating pressure is 3 bar. When the water pressure exceeds 3 bar, the appliance’s safety vent will open and discharge water. If the pressure does not remain stable, there may be a leak in the system or in the expansion vessel, and in this case you must call the authorised dealer or customer service agent. Usually any leaks will be from the system rather than from the combi boiler.
  • If the pressure falls below 0.5 bar, the appliance will show a fault and the relevant fault code will appear on the screen. Not all combi boilers are equipped with a low-pressure alarm, and therefore the pressure must be checked periodically. For example, once a week or once a month.
  • If the pressure is low, water can be introduced using the filling valve below the combi boiler. Make sure that the device is in waiting mode and is cold when you are adding water.

  • It is useful to keep it working at minimum output when there is nobody in the house because this will prevent the temperature from falling very low as a result of heat loss.
  • Using the room thermostat adjustment can be made to temperatures between 18-20°C for when there is nobody at home. The system can be programmed so that it will reach comfort temperature near to the time of your arrival at home (20-23°C).
  • The combi boiler must not be turned off using the on/off switch or the consumer unit, otherwise all protection functions will be disabled. It must be left in standby mode. Alternatively it can be put in summertime mode.

  • Using a natural gas combi boiler is more economical than other fuel types. An example of this would be an electrical boiler, an LPG boiler or a solid fuel boiler.
  • Using an LPG cylinder, an electrical heater, or a stratification cylinder in order to heat domestic hot water is more expensive than natural gas at current fuel prices.
  • Using a combi boiler equipped with advanced electronics in terms of safety and fuel consumption is a rather economical method of heating, especially if it is used in conjunction with a thermostat. Installation and operation of combi boilers is easy, and maintenance is simple and operation is reliable. Multiple installation options are available. The dimensions of a combi boiler are smaller compared with other appliances, and the fact that it can provide heating and domestic hot water without hot water storage gives it advantages in terms of investment and operational cost.

  • If a combi boiler breaks down, it will usually indicate the cause of the fault by displaying one of the fault codes stored in its software.
  • Such a fault code may indicate, for example, that the water pressure is low, and this can be resolved by adding water and resetting the appliance. Such guidance is provided by our Customer Communication Centre.
  • You can contact the relevant customer service agent or our call centre and give them the fault code. You can telephone the Buderus call centre at 444 5 474.
  • Service guidance is provided by the call centre.

  • A combi boiler cannot be installed in stairwells, on walls were there is a chimney, in apartment building light wells, in open balconies, bedrooms, or in areas where explosive or highly flammable substances are stored. They may be placed in outdoor areas, provided that they are confined in a protective cabinet.
  • Condensing appliances with outputs of more than 50 kW which receive their combustion air from the external environment must be installed in a dedicated location which is only used as an appliance room, and the electrical switch must be located outside that area. Condensing appliances which receive their combustion air from the external environment must have a grating measuring at least 150 cm2 opening to the outside atmosphere in the vicinity in which they are installed.

  • Gratings open to the outside atmosphere in the location where the combi boiler is situated which must not be covered. Care must be taken to ensure that neither the flue connection nor the gas connection is disturbed.
  • The consent of the relevant gas company must be obtained for any change in the installation or a change of combi boiler replacement, and leak tests must be carried out.


  • Ideally one should calculate the heat loss of the home, and to place radiators in the most appropriate positions in the rooms. Heat loss varies according to factors such as how well your home is insulated, its orientation, its construction materials, and other criteria.
  • If low-temperature radiators have been selected, this will require a larger radiator surface and you can readily opt for a condensing boiler. When selecting radiators, it must not be forgotten that the heat they provide will depend upon the temperature of the water.
  • The heat loss of your home is an important criteria when selecting a heating appliance, but the required combi boiler outputs will also depend on the domestic hot water output required. For example, the heat loss of an average 100 m² home may be 10-12 kW (and with good insulation this can be reduced to even 5 kW) Combi boiler capacities are in the range 20-24-28 kW. This is because they need more energy than that required simply for space heating alone. If the heat loss of the house is very low, for example 5 kW, and we are going to buy a 24 kW combi boiler, we must choose a combi boiler with the widest possible modulation range.
  • If the domestic hot water requirement is high, that is to say if there are 2-3 bathrooms in the house and it is likely that they are going to be used simultaneously, you must choose a large output combi boiler. For example, taking a shower requires a flow of 8-10 L/min.
  • An expert heating installer will be able to give you this sort of advice so it always pays to consult a specialist.

  • In conventional combi boilers, after combustion the combustion gases are expelled from the flue at high temperatures. Within this waste gas there is some water, and this water vapour contains energy.
  • Condensing boilers condense this steam, that is to say they convert it to liquid, and in doing so they recover the energy within it. The boiler transfers the absorbed energy to the water circulating in the system, which passes into your radiators. So the boiler extracts as much of the energy available in the fuel as possible, and puts it to use. The water returning from the system meets the burned flue gas and cools it to the temperature of the system water.
  • In order to make the condensation process work, temperature of the return water must be 55°C or less. This means that the emitter surfaces must be appropriately selected, and larger radiators are generally the right choice for a condensing boiler. Also, when using condensing combi boilers, the temperature of the heating flow water must be adjusted in order to benefit from the condensing energy (a maximum of 60-70°C).
  • In condensing combi boilers, the condensation occurs within the combustion chamber and therefore the materials must be resistant to corrosion. This is the reason why they are more expensive than conventional combi boilers.

  • Condensing combi boilers are suitable for all homes. But the system must be designed so that the return water is at 55°C, so it is important that the user makes their selection accordingly. Otherwise, if throughout the year the boiler is failing to condense, it will not be able to perform at full efficiency.
  • Clearly more condensing energy is used in homes with high heat loss because more energy is consumed. Condensing combi boilers very quickly pay back the price difference from a conventional combi boilers.
  • The use of modulating room controls is recommended in order to obtain the highest efficiency from condensing combi boilers. In this way, the temperature of the flow water can be adjusted according to the radiator dimensions so as to get the benefit of condensing efficiency on more than just very cold days.

Both types of combi boiler are suitable for apartment building flats, but do not forget that condensing combi boilers offer greater fuel savings. For a normal apartment building flat one can choose a 20-24 kW conventional or condensing combi boiler.

A hermetic combi boiler is an appliance equipped with a fan, which draws its combustion air from outside. Conventional combi boilers are generally known as «hermetic» but both conventional combi boilers. and condensing combi boilers can be equipped with a hermetic flue system. Conventional combi boilers burn natural gas and expel the exhaust gas, but do not benefit from condensing energy. But new generation conventional combi boilers are being rendered efficient with modulating fans, controls based on room temperature, and other features. Condensing combi boilers are 10-11% more efficient than conventional combi boilers. In practice savings of up to 30% can be achieved.

  • When buying a combi boiler the most important criteria is efficiency, and it is worth buying the most efficient combi possible. Consequently, it is essential that you consider condensing combi boilers.
  • The question of whether they are equipped with single or double heat exchangers may not be so important. A double heat exchanger may increase domestic water comfort. That is to say, a double heat exchanger combi boiler provides domestic hot water at the required temperature more promptly. But it would not be correct in terms of durability or efficiency to discriminate between single and double heat exchangers in a conventional combi boiler.
  • It may be important that an appliance located in a kitchen or an area of the house where you spend time should operate with low noise. The start-stop sound and sound of water circulation can be annoying.
  • Efficiency aside, important selection criteria are that the combi boiler must be easy to operate, that it shows error codes in a clearly understandable manner, that it can be used with modulating room controls or outdoor controls, and that it should have a long service life. In some locations the dimensions may also be important.

  • Conventional or condensing combi boilers may be used in detached houses but because the heat loss is greater, the heat requirement will be high, and therefore a condensing combi boiler will be more economical.
  • If comfort in terms of domestic hot water is important (for example, if there are several bathrooms or a Jacuzzi) then it may be worthwhile having an appliance equipped with a cylinder. Since water will be stored in advance, you can draw more hot water per minute, and there will be no fluctuations in temperature. In some detached houses, a wall-mounted boiler with integrated or external cylinder will be a more appropriate solution in terms of comfort.

More important than the size of the family are factors such as the size of the heat loss of the house, its orientation, construction, height etc. In calculating domestic hot water requirement one must look at the number of bathrooms and the likelihood that they will be used simultaneously. The higher quantity of water per minute that the appliance is required to produce, that is to say, the greater number of taps which can be open at any time, the greater the output of the combi boiler must be.

It is important that you consider the number of customer service agents that the company has, how they are distributed, the level of competence of the customer service agents, and the availability of spare parts. It is also important that there is a call centre which can provide you with support and assistance in finding solutions.


In order to make natural gas savings, the main priority is to minimise heat loss in the building. The way to prevent heat loss is to insulate well. The ideal situation is to buy a high efficiency appliance and to have your home well insulated.
Condensing appliances provide greater fuel savings than conventional appliances. Operating the appliance at low temperatures will increase the efficiency of the appliance.
Another important factor is using a thermostat. Using a thermostat ensures that you produce no more heat energy than is necessary. Using a modulating room thermostat means that when the room approaches the set temperature, it modulates, the output of the appliance is reduced, minimising the number of start-stop cycles, and cutting fuel consumption.
If the boiler is operating with an outdoor thermostat, then the temperature of the heating flow is determined by the thermostat on the basis of a mathematical curve based on the outdoor temperature, so in cold weather the boiler produces water at higher temperatures, while in the heating flow is at a lower temperature in mild weather. This means that the boiler produces only as much heat energy as is necessary.

If the system is to be used with a condensing combi boiler, operation at lower temperatures will increase the efficiency of the system.
Pipe diameters and radiators must be selected correctly so that the heat transfer is carried out as efficiently as possible with minimum loss. If this is not achieved, it may not be possible to achieve the degree of heat that you want in every room.
That is to say, some rooms may be heated more than you want while some may be heated less than you want.Using a thermostat which operates on the basis of outdoor temperatures or on the basis of the room temperature means that the temperature of the heating flow is adjusted in order to attain the required room temperature, and if heating flow is adjusted appropriately the system will operate more economically.
Using a timer program ensures that the house is kept at a specified temperature when you are not there and this is also an economy.
Use of thermostatic radiator valves can also contribute.

The initial investment for a stove is less than that for a combi boiler system but you will need an additional appliance for the domestic hot water supply.
Natural gas is a more economical method of producing domestic hot water than electricity or LPG.
A stove provides local heating and therefore is not a heating method which provides comfortable heating. In terms of distributing heat, having radiators in every room offers more comfortable warmth.

In apartment buildings, communal systems are an appropriate method if the building is well insulated and the costs are shared. Each flat can be heated to the required temperature from a single communally operated central source and the costs can be shared fairly.
The use of combi boilers in flats where the insulation is poor may be more expensive for users due to heat loss.
In a communal system, some boilers may produce more energy than is necessary. In these circumstances it is important that the system has a broad modulating range and that it is equipped with an advanced control system.
For domestic hot water, a combi boiler is more economical.


There may be air in the system, and bleeding the radiators might solve the problem.
It may also be a circulation problem. The pipework may not have been installed correctly, with the result that radiators near the combi boiler get too hot, while the more distant radiators do not heat up sufficiently because the water never reaches them. In this case you will need a heating installer to solve the problem. Once the system has been installed, it is essential that the radiator valves are adjusted to produce the correct flow.

You can check whether the flame light on the combi boiler is illuminated or not. A continually flashing light indicates that there is a fault. It is possible that the combi boiler is not circulating. Deficient circulation may occur if the pump is blocked or has broken down.
Minimum capacity.

In combi boilers, the gas is supplied by the air/gas ratio control valve, the air required for combustion is provided by the fan and a fuel air mix is supplied to the combustion chamber. The ignition electrodes ignite the fuel air mixture to establish combustion. While gas is entering the combustion chamber, the ionisation electrode monitors the ignition, and if ignition does not take place, it prevents the entry of more gas from the control panel. If there is any problem with the electrodes, an error code will be displayed on the appliance screen.
If there is no problem with the electrodes, the problem may arise from the main gas valve.

Lack of thermal insulation results in excessive heat loss because heat is continually escaping through the walls and windows. The more resistant to heat conduction the materials of the wall’s construction are, the less heat passes through. Operating the combi boiler at higher temperatures results in higher fuel consumption. Using a room thermostat can also provide fuel savings if you adjust the room temperatures as low as you are comfortable with.
There may be heat transfer/loss between storeys and flats in buildings where a combi boiler is used and therefore heat will be lost to vacant flats, or flats where their combi boiler is operating at low temperatures.


A heat pump enables us to use energy in nature which we would not normally be able to use because its temperature is low because the heat pump raises the temperature of that energy. One of the most readily available sources of natural energy is air. Put simply, a heat pump is an electrical device which absorbs the low temperature heat energy present in the outdoor air, raises the temperature of this heat energy and transports it to the internal environment which is to be heated. That is to say, the electricity is not used to heat the internal space but rather to absorb the heat and carry it into the internal space. The process of distributing the heat in the internal space can most easily be achieved using water. That is to say, as with the combi boiler, you first heat the water, and then pump this heated water through the radiators in the location where heat is required, and so heat the room. The heat pump is also used for the distribution of the heat. It takes the heat it has absorbed from the air outside, loads it onto the water, and then circulates this heated water in the system and radiators within the space which is to be warmed.
Because of the way a heat pump operates, it comprises an outdoor unit which must be located outside the building in order to be able to absorb heat from the external air, and then an internal unit which includes a pump to circulate the heated water through the system. If necessary, this system can also include a primary store system (a hot water cylinder) in order to make ready the domestic hot water.

One advantage of a heat pump is that it can be operated in reverse. In other words, it can absorb the heat it has absorbed from an internal space and carry it outside, thereby reducing the internal temperature of the house. In other words, you can also cool your home in summer. However, in order to achieve this, the system has to be designed to be able to carry cold water and therefore must be suitably insulated. This is because if cold surfaces are not insulated, the moisture in the air will condense on them, causing those areas to become wet. Consequently, if both heating and cooling are to be achieved, the internal system requires more than just radiators or underfloor heating pipes. Instead of these elements, or in addition to them, there must be components which are suitable for both heating and cooling, specifically a fancoil and a drain connection in order to dispose of the water which condenses while cooling in summer. And it must be remembered that all of the pipes in the system must be insulated…

A heat pump is an individual and independent heating/cooling system. Consequently, it can only be installed in apartment building flats or villas with independent individually installed systems, or in business premises with similar arrangements.

Heat pumps use the heat in the natural air as its fuel, and uses electricity in order to transfer (or pump) this heat. A heat pump expends one unit of electrical energy for every four units of heat energy that it absorbs from the outdoor air and carries indoors. That is to say, a heat pump provides 4 kW of heating or cooling for every 1 kW of electricity it consumes, so we get four for the price of one, making it a very economical proposition. Currently, heat pumps provide the most economical heating and cooling in locations where natural gas is not available. The only downside is that the cost of installation is higher. If we compare the cost of a heat pump installation using split air conditioning units with a central heating system which burns solid fuel (wood or coal), the cheapest alternatives available on the west coast of Turkey where natural gas is not available, the difference in the initial investment cost will be amortised in approximately three years. Heat pumps are designed to operate with a mean service life of 15 years. That is to say, fuel savings will pay back your initial installation cost in approximately three years, and from then on you are in profit.

The Buderus Logatherm heat pump is a complex system comprising an indoor unit, an outdoor unit and a hot water storage cylinder. Underfloor heating, radiators or fancoil devices function as the indoor unit for heating purposes, while fancoil devices alone are used for cooling.
The Comfort series comprises four different capacities: 8, 11, 14 and 16 kW. In heating mode, it can heat the system water to 55°C, and cool it to 5°C in cooling mode. It can operate without problems for heating purposes with outdoor air temperatures as low as -20°C, and for cooling purposes, in outdoor air temperatures up to +46°C.
All of the elements required in a wet system (such as heating pump, sealed expansion vessel, vent, back-up heater, and filter) have been incorporated into the indoor unit. All of the components of the indoor unit are insulated against condensation with a rubber insulation material. This is a guarantee of a long service life.
One of the major features of Buderus Logatherm heat pumps is that the control panel is in the Turkish language and can be easily adjusted. If required, a room thermostat for individual room temperature may optionally be connected to the system.
The system also provides a domestic hot water solution, and hot water storage of 200 L or 300 L can be used.
The Logatherm Hybrid model can be installed where there is a pre-existing heating system. The heat pump is installed with additional connection and control facility so that it can operate simultaneously with the existing system.