35kW Combi boiler

35kW combination boiler – “R2C34” from Flexiheat UK – high performance domestic hot water output flow rate of 16 litres/min with a 30C temperature rise for commercial or domestic installations

Our modern 35kw combi boiler is a cost effective heating solution that employs condensing technology to effectively heat the system water by removing latent heat from the flue gases which enables these boilers to have a “A” ErP rating for space heating efficiency and “A” ErP water heating efficiency rating, which means higher efficiency and thus lower running costs and for this gas combi boiler.

A combination boiler is the most popular boiler type in the UK, as the size of a combi boiler is one of its main benefits. As Combi boilers do not require external hot water cylinders / water storage cylinder, this type of boiler provides both hot water and central heating in a single compact unit for more than one bathroom properties.

Having “heating and hot water” in one boiler has many benefits and will save installation space on site and the users or customers will have a lower installation cost as a combi boiler installation is quicker that a system boiler and indirect cylinder installation.

Our gas boiler has a great modulation or turn down ration of almost 10:1 in range, which means the boiler will match or address the central heating load requirement very closely with high efficiency, ensuring you’ll save money on your energy bills for heating and hot water.

With low noise level, this reliable gas boiler, which is available to natural gas or propane gas (LPG) will produce a domestic hot water output of 16 litres/min with a temperature rise of 30C and is up to 108.6 % efficient and provides a cost effective heating solution for domestic installations with tested technology.

35 kW Combination Boilers

A gas burner in the combi boiler is lit when you need hot water or heating. The primary circuit receives the heat from the burner through the main heat exchanger, where it is then either moved straight to the radiators or through a plate heat exchanger to your hot water taps in larger homes.

One of the key features of our 35 kw ErP compliant modern gas combi boiler is a “pre-heat” system, which enables the boiler to contain a small volume of water that can be used instantly for fast hot water response. The water is kept in the boiler all day and kept at the desired temperature so that it can be quickly delivered to the hot water taps.

Fuel options for our 35kw output gas combi boiler

This 35kw combi is available in either natural gas or LPG (propane) gas options depending on local availability of the fuel to the property or house. Should you ever need to change your gas type, just speak to our customer services as we can supply a gas adaptor kit to change the gas boiler to your required fuel type. This is an easy installation and takes less than quarter of an hour to do at most if ever needed as the unit has easy access to all internal components. 

Stainless steel heat exchangers in our combi boilers

Our full range of condensing boiler models use stainless steel heat exchangers because of their high corrosion resistance across a broad pH range and are better than a aluminium heat exchanger. Your combi boiler will last longer as a result and has a long warranty period, making them a good choice gas boiler for consumers who require a quality solution and  high domestic hot water output.

When discussing our combi boilers dependability, the development of our modern heat exchanger from one single continuous coil permits the water to move through more quickly, efficiently, and at a higher flow rate performance.

This reduces the possibility of debris blockages, increasing reliability and lengthening the boiler’s lifespan. A Stainless steel heat exchanger construction will withstand high flow rates without corroding or wearing out more than a aluminium heat exchanger.

Patented A rated ErP water heating efficiency

Inside the high performance patented stainless steel main heat exchanger is a 12mm diameter internal stainless steel pipe that produces domestic hot water (installed within the 28 mm diameter heating exchanger). This ensures you have a quantity (approximately 7 litres) of “warm water ready to go,” as they say. It’s total length is 8 metres. Because these boilers produce domestic hot water by continuously condensing, which makes them very efficient, gas energy costs and energy bills are reduced.

Additionally, these design features reduce the possibility of scale accumulation, which you can expect in older combi boilers with a plate heat exchanger that many companies still use.

In areas with hard water, this is crucial because our heat exchanger’s high velocity and flexing while in use reduce the potential for scale to build up and prevent it from happening, helping to ensure a long life, trouble-free operation, and a good hot water flow rate for domestic installations.

Good mains water pressure is needed for combi boilers

One potential drawback of a combination boiler is that if multiple showers and taps are initiated simultaneously due to combi boilers pulling water directly from the local availability in the mains cold water supply, the water pressure can drop quickly for example.

Our boiler needs a minimum pressure of 0.5 Bar and will operate up to a maximum pressure of 6 Bar. For good hot water performance we recommend around 3 Bar pressure for your hot water system.

Boiler specifications, features and details

Our 35kw heat output combi boiler has both “A” rated ErP water heating efficiency performance for both heating and domestic hot water, with low noise level outputs and is suitable for weather compensation, when used in conjunction with the external temperature sensor that we can supply for our full range of heating and hot water boilers. Weather compensation reduces the heat output to suit the weather conditions which can vary so much on a day to day basis in the UK.

This 35 kw boiler range is suited for space heating or central heating with radiators or underfloor heating systems with a high efficiency of 106.43% when used on a 50/30C range flow and return system which will save you money and cost on your gas energy bills.

With a useful central heating output of 36.19 kW when used on a 50/30C system , or when used on a 80/60C system the central heating output is 33.35 kW.

We use a Wilo pump rather than a Grundfos pump in our 35kw gas combi, as we consider them a more reliable pump than a Grundfos pump.

Download the Flexiheat R2C 34kW Combi Boiler Manual

For larger homes, or homes that have larger hot water performance demands then please look at our next size up combi boiler our – 50kW gas combi boiler

Dimensions

Our 35 kw combi boiler dimension are – Height = 642 mm , Width = 410 mm  and a Depth of 350 mm – with a weight of 44 kg making these robust units easy to fit in any installation.

Flow and return and gas connections – 20 mm

Hot and Cold water connections – 15 mm

Flue lengths and options

With extensive flue options of up to 60 metres in length – when using a sperate 80mm diameter twin flue system, or up to 10 metres in length when using our 80/125mm co-axial horizontal flue system option – both options make this combi boiler a room sealed gas appliance.

Horizontal flue kit co-axial – the 80/125mm Ø will go 10 metres

Or our vertical flue option

Vertical flue kit co-axial – the 80/125mm Ø will go 10 metres vertical

Control options

This boiler can be controlled via the inbuilt digital display, which displays digital operating status and diagnostic display or you can opt for our smart thermostat range option, which is an OpenTherm control system, that allows you to control these combi boilers from an app on your phone, tablet, or computer.

Cloud Warm App – control on the go !

Nest and Hive controllers are Opentherm compatible, so you can use them with what we consider the best 35 kW combi on the market and a cost effective heating solution for homes heating

Common question

35kw combination boiler how many radiators can it run ?

The average size radiator in a new build property is now 1.5 kW (kilowatts) output – so your looking at 23 radiators, but for older properties your looking at around 11-15 radiators on average for this size gas boiler type.

Please ensure that the local area boiler installer or a company engineers are gas safe registered and can provide a labour warranty and service agreement on the install.

Contact us for free boiler quotes for your combi boiler requirements

Should you require anymore assistance, information or best deals/prices on the best 35kw combi boiler with great hot water performance in natural gas or LPG gas on the UK market, please contact our customer services sales team on 01202 822221 or use our email contact above on the web page for our email contact form. All of sales are supplied with a vat invoice.

LPHW Unit Heaters

A LPHW (which donates Low Pressure Hot Water) heater is fed by a hot water system. A boiler, which can be a gas or oil boiler, biomass boilers or a heat pump, is the external warm water heat source used by these water heaters. The warm water is transported to the LPWH unit heaters by the heat source. Then a fan disperses the warm air throughout the area being heated, such as exhibition halls, production lines, sports halls , warehouses, garages and many other commercial or industrial buildings that require heating.

LPHW heater

In gravity feed systems, the flow and return pipework pressures for LPHW are frequently less than one bar in operation and 2 to 4 Bar in pressurised heating systems.

Our lphw unit heaters can operate up to a maximum pressure of 16 Bar with various discharge options – either downward discharge (vertical installation) or horizontal discharge units.

We also do an air heater version especially for a heat pump system, that has a larger delta T flow and return system, that these heat source systems can operate on.

Warm air flow

This cost effective water fed unit heater range are fitted with a three speed energy efficient fan installed on every model. The fan motor speed is controlled by optional control accessories, which range from a basic control option to a full BMS (Building Management System) compatible control model, which is frequently required and suited to commercial and industrial warehouses.

All of our manufactured controllers have temperature control, to turn off the air heater or heaters when they reach a certain temperature, or to modulate the fan motor on the units as required.

Product Construction

Because it is specially developed and made of expanded polypropylene, it weighs up to five times less than a conventional steel cased unit heater at the larger heat output sizes. This makes installation of the fan coil unit space heater easy even in tight space configurations.

Both these accessories make installing these heaters an easy task in warehouses or factories, especially when a unit heater mounting position may be required directly over production lines or to avoid pallet racking, etc.

Heat exchanger

The heat exchanger in this extensive range of warm water heaters , made of copper with aluminium fins, ,which guarantees optimum heat output with high efficiency from the equipped heating coils. The air flow generated by the fan and motor is directed through the adjustable louvers fitted to the heaters into the rooms being heated.

The heat output of this extensive range of unit heaters for low pressure hot water systems is directly related to the heating hot water temperature, which is used to supply the unit heater or heaters.

Our units can work with a warm water medium temperature of 120 C and a maximum pressure of 16 Bar, so LPHW heating is not a problem for these units.

The fan speed of the unit heater, as well as the air throw of the model, influence the leaving air temperature and heat output of the unit heater.

We do steam heating models, which are listed on their own dedicated webpage here: steam unit heaters

Installation

Address all conceivable likely space configurations that require heating with two discharge options—horizontal or downward (installed hung from the ceiling).When air flow from a horizontal warm water unit heater might be impeded by obstacles in complex areas such as exhibition halls, downward discharge is especially well suited.

LPHW heater for directional heating with a downward discharge installation – we can accommodate all likely space configurations or complex areas

However, where directional heating is needed, horizontal discharge units with adjustable louvres are ideal and are the most popular installation configuration for this range of heaters.

Horizontal discharge units

The standard bracket supplied for the horizontal unit is an adjustable rotating console that allows for 170° rotation of the unit heaters and allows for directional heating as well as the adjustable louvers.

The bracket can also be used in a downward discharge from a ceiling installation, or we can provide other accessories like corner brackets that let the air unit heater be connected to the ceiling with threaded bar drop rods.

Horizontal discharge units – our “Leo” unit heaters EPP Plastic cased from Flexiheat UK

According to the HSE, domestic hot water must be kept in the cylinder at a minimum of 60 degrees Celsius to destroy legionella bacteria , which unfortunately can be fatal for human beings.

Therefore, the best temperature or ideal temperature for your hot water tank is 60 °C, as 90% of the bacteria will die in only two minutes if the hot water tank temperature is 60 °C. If the temperature of the hot water tank is raised to 70 degrees Celsius, all of the Legionella bacteria will die right away.

Hot water tank temperature for your hot water cylinder

In the UK, the hot water tank’s temperature should range from 60 °C to 65 °C.

There is a higher chance of bacteria like Legionella, which causes Legionnaires’ disease, developing if the temperature is below 50°C. When your water has been sitting in the stored hot water tank for some time, this occurs.

The water will be too hot to use and the danger of severe burns will rise if the temperature rises over 65°C. The water is hot enough to use and hot enough to destroy harmful bacteria when kept at a safe temperature of 60 °C to 65 °C.

Hot water cylinders or tank

Hot water tanks must now be equipped with a thermostat that allows the user to control the temperature of the water within. You can monitor the hot water tank temperature of the tank on your phone these days using a hot water temperature sensor installed in the hot water cylinder.

Cut away picture of our indirect cylinder Flexiheat UK

Our indirect unvented cylinders or direct unvented cylinders that we supply both have a thermostat to control the hot water temperature to your requirements.

Legionella, what is it ?

The word “legionellosis” refers to a group of illnesses brought on by the legionella bacteria, including the most severe one, Legionnaires’ disease, as well as the comparable but less dangerous Pontiac fever and Lochgoilhead fever. The potentially lethal pneumonia known as Legionnaires’ disease can infect anyone. Age-related risk is higher for certain people than for others, such as:

1. Any person whose immune system is compromised

2. Those with chronic kidney or respiratory diseases.

3. People suffering from cardiovascular, pulmonary, and diabetes diseases.

4. Those who smoke and drink heavily.

5. Individuals who are over 45 years of age

In natural water sources, including rivers, lakes, and reservoirs, the bacterium Legionella pneumophila and related bacteria are widespread but often in low concentrations. They may also be found in specially designed water systems, including spa pools, evaporative condensers, cooling towers, and hot and cold water systems.

In order to reduce the dangers of legionnaires’ illness, it is crucial to eliminate favourable circumstances for legionella risk.

How does one get legionnaires ?

People get Legionnaires’ disease by breathing in aerosolized water droplets (aerosols) that are suspended in the air and carry the bacteria. The following circumstances raise the risk of legionella:

The hot water temperature in the system may range from 20 to 45 °C in the hot water cylinder or domestic hot water system, which is ideal for development.

It is possible to produce and disperse breathable water droplets, such as aerosol, from a cooling tower or hot water outlets, such as sink taps, bath taps, or showers.

When water is stored and/or recirculated, deposits like rust, sludge, scale, organic waste, and biofilms can help bacteria grow and feed the organism.

Thus, it is vital to reduce the risks to the health of individuals, be they staff or customers on your business site, or home owners or occupants.

The majority of people who become ill and require hospital treatment ultimately survive and recover completely.

However, roughly one in ten individuals who contract Legionnaires’ disease passes away from the illness.

What temperature should domestic hot water be in the UK

We’ve established that is hot water tank temperature should be 60 C to 65 degrees Celsius which means that any gas boilers or oil boilers should be supplying the indirect cylinder with a hot water temperature above that figure to ensure the cold water coming into the hot water cylinder gets heated up to the right temperature.

Alternative methods of heating the hot water tank, such as a solar water heating system or heat pumps, are also becoming more common these days as we look to reduce and save carbon emissions from gas boilers or oil boiler heating system.

There are some issues with regards to using heat pumps instead of a heating boiler, as they can struggle to heat the water system, as at present the maximum heating temperatures of a heat pump are around 55 °C, which means they don’t generate the right temperatures required for domestic hot water heating.

This is remedied by using an immersion heater to raise the tank water temperature from 55 degrees Celsius to the required 60 degrees Celsius.
The immersion heater or heaters, depending on the hot water tank size, are normally electrically supplied with power.

Combi boilers, on the other hand, produce hot water on demand and have no stored hot water tank. Thus, these types of gas or oil boilers can supply the hot water system at lower hot water temperatures , which also helps save carbon emissions, energy and money for your economical domestic hot water heating system.

The hot water tank accounts for 14% to 18% of the energy consumed by the typical household.

Domestic hot water systems in the UK

There are two main systems for heating hot water used in the United Kingdom.

Stored domestic hot water

normally produced via a boiler in conjunction with an indirect cylinder. The thermostat on the hot water tank controls the boiler, which you simply adjust to your requirements.

On demand or instant hot water:

An on-demand water hot system normally saves energy and money ( normally around 30% less energy when compared to hot water storage systems ) as they efficiently allow the bath, shower, and tap water supply to be at a lower temperature—around 40C to 43C while washing. This warm water temperature eliminates the risk of scalding when having a shower, bath, or using a hot tap as this heated water is under the supply temperature of 44°C at which scalding risk to vulnerable people can occur.

Instant water can be provided by a gas water heater , which we have a full range detailed on this dedicated webpage: gas water heaters , which are available in natural gas or LPG (Propane) gas.

Gas Water Heaters

In many households in the UK , a combi boiler or combination boiler is the most commonly used appliance as they do both the heating and water system. The boiler has a thermostat, which allows temperature control of the DHW water.

This thermostat dictates the water temperature to the supply pipe running to your warm water outlets, such as your hot water tap, shower, or bath tap.

As the boiler doesn’t have to heat the water up to 60 °C like a stored warm water tank, they benefit from lower energy requirements and eliminate scalding potential .

Our combi or combination boilers are detailed on this webpage: LPG combi boilers. We also do these units in natural gas too.

Combi boiler  from Flexiheat UK

Conclusion

The hot water temperature for your hot water tank will be different to the hot water temperature used on an instant water heater , as the stored warm water must be 60C or over, and when producing it on demand , it can be lower, circa 40-43C, depending on your requirements to save energy.

If you are looking for a main multipoint BF water heater, then the bad news is that these gas fired water heaters are no longer available, whether it was the standard model, which was obsolete in 2018, or the ERP model, which was discontinued in 2019.

This gas-fired instantaneous water heater brand and model was an advanced balanced flue 24 hour a day space-saving on-demand water heating unit with no storage tank and a copper heat exchanger.They were a hot favourite for hot water heating for small homeowners’ domestic needs as they eliminated the requirement for a separate hot water cylinder and had a modern room sealed design.

The balanced flue water heater had a Piezo igniter and a permanent pilot. This meant that it didn’t need electricity or batteries.

In these main hot water heaters, the pilot light always stayed on. Because the pilot flame was continually on, this burned up and squandered gas, which was bad for energy bills and the environment.

A few years ago, “Which” consumer magazine conducted a cost analysis that revealed that a pilot light cost an incredible average of £97 per year to run.

The ErP legislation for efficiency with regards to water heaters means that permanent pilot water heaters mean that these types of units no longer meet the required efficiency levels, which is the reason why they are not available anymore.

Electronic ignition models now prevail, and due to the elimination of pilot lights, they end up saving money on running cost.

Now the water heaters must have an electricity supply – just a standard 240 volt – 1 Phase supply.

Main multipoint bf gas water heater

There are some companies offering spare parts for these advanced balanced flue main water heaters, such as the gas isolation valve kit, the thermocouple kit, overheat protection device kit, air vent, and main heat exchanger ( although the price of a replacement heat exchanger is more than a new replacement water heater—i.e., to replace the heat exchanger is no longer viable as the item costs more than a new gas-fired water heater, let alone the cost of a plumber to fit the replacement spare parts)

Should you need to check the gas supply inlet pressure or burner pressure to make sure that the rate of gas is correct, or change the gas isolation valve, then this needs to be done by a qualified gas safe engineer.

It is important to ensure that any suitable service or services such as replacing parts on gas water heaters or gas-fired central heating boilers, should not be attempted by a homeowner or a plumber that doesn’t have the gas safe plumbing qualification.

Main multipoint water heater

A balanced flue system

On demand gas water heaters that employed balanced flues are made up of two pipes with one pipe contained within the other. The outer pipe brings in the fresh air from the outside that is necessary for the combustion process to occur, while the inner pipe serves the purpose of removing the waste gases from your property. Depending on the main instantaneous water heater you purchased, the designed flue system may either go horizontally through an outside wall or vertically through the roof to suit the customers requirements.

The balanced flue model had to be installed on a wall with direct access to the external air environment-see diagram below.

Balanced flue kit details

Main also did a fan flued version of this gas water heater, which was designated the main multipoint FF ( fan flue) —this unit is the one that could be vertically or horizontally flued and didn’t need to be installed on an outside wall of the property because of the fan flue system.Again,these fan flue water heaters were a hot favourite with homes or locations that had a big demand for hot water but didn’t want to use a hot water cylinder or storage cylinder.

Main fan flued multipoint – Flue options

Hot water instantaneous heater – Balanced Flue Main Heater

So now for the replacement of the Main multipoint water heater in its balanced flue version. Firstly, the dimensions of the unit are

Main bf multipoint water heater dimensions

and for our replacement unit – the SF14 Low NOx gas fired water heater with its modern room sealed design.

As you can see from the above dimensions, our SF14 Low NOx is smaller in size, yet still has plenty of room for the unit to be maintained and to service, with all the plumbing connections at the bottom of the unit.

SF14 – tankless water heaters from Flexiheat UK – Internal picture of the hot water heater

SF14 Product benefits and features

• Wet chamber copper exchanger that prevents thermal inertia; With large 16mm diameter water ways – so it benefits from very low pressure drops, guarantees lower risks of clogging,greater thermal efficiency, and greater ease of cleaning.
• Self-diagnostic electronic board;
• Ease of access and maintenance;
• Possibility of integration with other renewable energy source (e.g. solar panels)
• Possibility of remote shutdown;
• Overheat protection device
• Reduction of initial overtemperatures with low withdrawals:
• Degree of electrical protection: IPX4D;
• Very low NOx emissions, maximum 50 mg / kWh.
• Modern room sealed design

Because of their sleek, refreshingly modern designs and outstanding reputation for reliability and highest quality this versatile range of water heaters has siting flexibility with various flueing options.

Download the SF14 Low NOx gas fired water heater manual Flexiheat UK

Hot water performance table

The main water heater will produce the following hot water rates, depending on the temperature rise as per the table below.

Our SF14 water heater model , which has a Domestic maximum nominal heat output of 24.5 kW will produce the following hot water flow rates.

Water heater gas supply

The main multipoint bf water heating unit, as far as we can see from the details, was only available in natural gas, which is category or classification G20 . This is what we refer to as natural gas in the UK, and is the gas that flows from the main gas supply services, or network.

Our replacement for the main multipoint bf or the fan flued models can be powered by either natural gas or propane gas ( LPG ). The LPG version can be fuelled by either a 47Kg propane tank or cylinder , or alternatively by a bulk storage propane tank.

We keep stock of our SF14 low NOx gas water heaters in both gas types in our warehouse , ready to service any immediate order without delay.

Experts in the water heating industry

If you require any more info, correct hot water heating solutions advice, check stock, delivery times, require trade prices or order your replacement for the main multipoint BF water heaters, range then please use the contact us form page on the website, or alternatively feel free to contact our customer service team experts a call on phone number 01202 822221-Flexiheat UK.