50kW Boiler

50 kW Gas Boiler

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Our 50kW boiler, covers the larger end of the domestic boiler market, and lets you expand into the light commercial boiler requirements that you may have. They are ErP A rated condensing boiler with efficiency up to 108.8 % at 30C return, with key features such as a stainless-steel heat exchanger, fully modulating 10:1 range – which is perfect for heat loading matching ensuring a long and efficient product life cycle and reduced running cost. They are low NOx emission boilers, class 6 – which means they have the least impact on the environment. Available in natural mains gas or LPG. They can be used in a multi boiler cascade system if so required.

50kW system boiler

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50kw System Boiler from Flexiheat UK – Gas Fired

A system boiler, has a separate unvented cylinder for producing and storing domestic hot water. This ensures that a consistent supply of hot water can be delivered to a large number of showers and taps simultaneously. As a result, a its an excellent choice for a property with multiple bathrooms, that require higher domestic hot flow rate.

System boilers do away with the requirement for a water tank in the loft since they get their water straight from the mains (which is required with a regular boiler). They then heat the water to provide warm water for the cylinder as well as central heating.

You have to install a heating expansion vessel on the installation (by others) which is usual at this output boiler.

System pressure for the hot water is mains water pressure and the stored water gives an excellent flow rate, which overcomes some of the problems with combi boilers.

Because combi boiler they are only really meant to sustain one hot water outlet at a time, they are not well suited to households with a high demand for domestic hot water. Heating performance may well be reduced in high-usage households because combi boilers routinely switch the burner from the heating system to hot water when there is a hot water demand.

This boiler can be matched up to various sized cylinders to suit the home requirements for heating and hot water outputs, with effortless comfort.

However, should your flow rate requirement be under 20 Litres / minute, then a combi boiler could be the best option, as a combi boiler produces hot water on demand – look at our 50kW combi boiler webpage for more information. A combi boiler does both heating and DHW, and is a ErP A rated for reduced running cost.

Key features of our 50 kw gas boiler

Natural Gas or LPG fired

Our efficient boilers are available in natural gas or LPG (Propane) powered units


The boilers output range is 49.19 kW down to 4.83 kW on an 80C/60C heating circuit, or 53.40 kW down to 5.15 kW on 50C/30C heating circuit

50kw gas fired system boiler- R1K50 model - technical data chart - Flexiheat UK; 50kw system boiler; worcester greenstar 8000; worcester bosch; greenstar 8000 life;

50kw gas fired system boiler- R1K50 model – technical data chart – Flexiheat UK

Modulation up to 1:10

For greater efficiency and reduced consumption both in heating and in domestic hot water production, when used with hot water cylinders

Low Class 6 NOx emissions-

NOx is a catch-all term for nitrogen oxides, which primarily include nitric oxide (NO) and nitrogen dioxide gas (NO2), our boilers have the lowest class emissions

System Pressure

Can operate on a heating circuit with a minimum pressure of 0.3 to 3 Bar maximum

Quality components

All boiler sub components are leading brand products and are selected through careful research for a guarantee of quality and reliability over time

An improved display screen

With push control buttons – for easy control of this 50kW gas fired boiler. With fault codes , for fault finding if there’s ever a issue.

Unrivalled quality / price ratio

The best boiler performance at affordable prices

A wall hung boiler, with modern upgraded controls, that make it one of the most efficient and also one of the quietest boilers manufactured on the UK and Irish markets – at only 52 Decibels – which makes a difference with quieter operation.

Heating output –

The boiler power will modulate the heat to the demand of the customers heating system installation, as the boilers output power range will go from from 50kw down to 5kW

Because the heat requirements of a boiler do not remain constant throughout the year owing to changing seasons, it may only be running at 20% of its capacity when it is warmer or at 80% when it is colder, our fully modulating 50kw gas boiler adapts to the heating system requirements, providing higher efficiency and reducing cost through wasted energy consumption.

Heating and Hot Water

Heating and hot water is provided by the boiler, via an indirect cylinder / calorifier – The heating side will heat your radiators or underfloor, whilst providing heat for the coil for the indirect cylinder


We do a range of controls that make your life easier, when it comes to controlling your boiler, from a basic room thermostat / programmer, with push control buttons all the way up to enhanced wireless internet controllers, such as Nest,Hive or bosch easycontrol thermostats, with features that provide you with the ability to regulate and control your heating from any extended location away from your home


We do a full range of flue options, such as horizontal or vertical kits, that ensure installation in the home easy – they are 80 mm / 125 mm outside diameter concentric – thus room sealed

Space required for installation

This 50kw heating boiler range is compact and modern, through award winning innovation in design and operation, it is also one of the quietest boilers to date on the UK and Irish markets -allowing you to locate the unit in any room and keep you cosy in the cold winter months.

50kw Gas boiler - R1K50 Dimensions Flexiheat UK; worcester bosch; worcester greenstar 8000; greenstar 8000 life;

50kw Gas boiler – R1K50 Dimensions Flexiheat UK


Pipework connection detail

Pipework connections for the R1K50 gas boiler; worcester greenstar 8000; worcester bosch; greenstar 8000 life; registered in england; quote;

Pipework connections for the R1K50 ( at the bottom of the unit )


Download the Flexiheat Manual for R1K 50 Gas Fired Boiler

Frequently asked questions

How many radiators can a 50kw boiler run?

The number of radiators a 50kW output boiler can run, will depend on the property. The average sized radiator in a new build home is 1.5kW output, thus newer properties the boiler can run 30 rads to be safe. With older less insulated properties, you’re looking at around 18 to 20 rads, click here for more details

Is a higher kW boiler better?

Boiler are sized to overcome the heat loss from the property ( normally at -5C outside, to give an internal temperature of 20C) in the previous years , you could oversize a boiler, which was not good for efficiency and your fuel bill, but these days the quality end of the market ensures that the boilers are modulating, which means they will operate down to some very low outputs – our 50kW gas boiler will operate down to 4.83kW flow rate, which ensures better heat load matching of the system, with high efficiency and lower running costs , click here for more details.


We normally deliver the boilers on a small pallet service to prevent any damage, for a middle England postcode for example this is around £45, on a 2/3 day delivery date service. Other postcode areas such as the Scottish Highlands / Low Lands, or postcode areas for West Wales and Cornwall as more as it costs us more to send to these areas. For Isle of White, Channel Island, or Isle of man postcode areas, please consult us for more information on a carriage quote.

Gas safe registered engineer

As always, we insist that any gas boilers are installed by a gas safe engineer, not only for the interest of safety, but also for the fact that it’s a legal requirement for the gas installation to be done by a suitable qualified person, so you can sit comfortably, knowing you heating and hot water system is safe. See here for the gas safe website.

Flexiheat UK

Should you require any more information on our 50kw boiler, then our sales team is available (Trading hours -Mon Tue Wed Thu Fri – 8am to 5 pm) to give you a quote and check stock details. Please follow us on Facebook to keep up on our news, reviews etc.

Maximum current watcher system for our electric boilers

Maximum current watcher system for our electric boilers

So a UK home typically has a 100 Amp supply fuse , this means that all the home electrical appliances , whilst being used simultaneously should not draw over 100 Amps , otherwise the fuse can blow.

Following is a chart showing the electrical ratings of commonly used household appliances –

Firstly Electric Showers- these can have some high loads

Standard Shower Rating Watts (kW)          Maximum load from the supply (Amps)

6kW                                                                      26

9kW                                                                     39.13

9.5kW                                                                  41.3

10.5kW                                                                45.65

11.0kW                                                                47.82

Standard electrically powered items, such as laptops, mobile phone chargers, Televisions (42″ HD), printers and radio’s etc only use approximately 0.5 amps, and don’t generally cause a problem in relation to your electrical loadings, but the following list of appliances and the amps they can draw on a single phase electrical supply, will have –

Domestic Electric AppliancesAmps Used
Radiator ( Electric )8.5
Hair dryer10
Washing machine10
Tumble dryer11
Vacuum cleaner9
Radiator (oil filled)13

UPDATE – We have now solved this common problem 
So why does this matter ? Well it matters because the larger the electric boiler you go in size , the more Amp’s you need available to power the boiler . You will generally find that in a standard 100 Amp – 240 Volt , single phased supply property , the largest boiler you can use is a 10 kW Boiler ( now a 15kW boiler-see the update below in red ) – why ? because this boiler will draw 45.5 Amps , which is getting close to half of the supply for a standard UK property , even when you consider a diversity factor ( which in layman terms means that not every electrical appliance would be on at the same time ) you are starting to possibly exceed your supply and tripping out fuses etc.

We now do a new range of electric boilers for central heating and / or domestic hot water, designated the “FHEL” range that can now utilise what we are calling the ” maximum current watcher” – it is basically a releasing relay (restriction of current). The relay monitors and controls the electric voltage in the whole house or flat and in the case of exceeding the permitted values of the electric current it reduces the input power of the electric boiler. All of this is done automatically, without any human intervention needed.This system will not only operate on our 240 volt / 1 Phase Electric boilers , but also our 400 Volt / 3 phase units as well. This now means that you can use our 15kW electric boiler model, in a property or flat with standard 240 volt, single phase with no worries or problems that the unit will trip out the main electric board.

For full details on this maximum current watcher, please download the following data sheet / instructions

Maximum Current Monitor – Instructions- for electric central heating boilers from Flexiheat UK

What are my other options? Well the best solution would be to get your electrical supply upgraded to Three Phase – Is it possible / How much is it to do this? I don’t know , we just supply the boilers – please contact UK Power Network , who are responsible for this here

Or another option may be to get a second 100 Amp supply to your property – Again , contact UK Power Network on the link above – this option may well work out cheaper than having three phase supplied to your property.

This system is used on our electric boilers – please see this webpage – https://www.flexiheatuk.com/product/electric-central-heating-boilers/


Lpg combi boiler – gas boilers – lpg boilers

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LPG combi boiler range – R2KC from Flexiheat UK


There are over four million properties in the United Kingdom that aren’t connected to the mains natural gas network – and this is where LPG boilers, specifically LPG Combi boilers provide a viable solution to power your central heating and water heating requirements where a natural gas boiler can’t be installed.

There are other options such as electricity, wood, solid fuel, or oil boilers that can be used for off mains gas grid homes, but the most common boiler for these properties is a lpg combi boiler. This is due to the fact that LPG combination boilers not only produce less carbon emissions, thus reducing your home’s carbon footprint, they also save money as they are the most cost effective to purchase and install.

This is why lpg combi boilers are the most popular new boiler for heating and hot water on the UK market, for properties that have no direct access to the main gas grid.

These lpg combi boilers are the ideal boilers to provide heating to a central heating system be it radiators or an underfloor heating system and also heat water for your domestic hot water requirements – Thus the term a ” lpg combi boiler” as they supply both requirements.

How do lpg boilers work? quiet simply the same as a natural gas one – except the key difference – its fuel is LPG rather than natural.Get a new lpg boiler now.

Combination boiler lpg

Combi boilers are designed so you don’t have stored hot water, so there’s no water tank required. They heat the water on demand, which ensures high efficiency and lower heating bills, with the flow of water they can heat is related to the power output of the condensing boiler.

By not having stored hot water in a tank, they are more energy efficient as they are only heating the water that supplies your hot water taps or shower when you require it.

These days all boilers lpg combi type are all manufactured as a condensing boiler, to get the maximum high efficiency from not only the heating system but also the domestic hot water production too. As new lpg boilers are burning fuel at this high efficiency, the result is lower heating bills, due to the condensing function of the boiler. This also reduces carbon footprint in a new boiler, when compared to an older non condensing oil boilers lpg boiler that aren’t condensing in function.

Our condensing lpg boilers achieve efficiencies of 105%, with many benefits such as a lower noise output than the majority of the lpg boilers on the UK market, and a patented stainless steel boiler heat exchanger, which is a pipe in pipe design, unlike some of the competition that use an inferior aluminium silicon heat exchanger. Our boiler lpg erp rating is “A” for both heating and hot water, which has replaced the old style lpg combi  5 stars max central heating and 5 stars max domestic hot water rating method used for combi boilers lpg fired.

Gas Boilers – Unique Heat Exchanger

The 12mm diameter internal stainless-steel pipe where domestic hot water is produced, is inside the patented main heat exchanger (28mm diameter). Its total length is 8 meters and this ensures you have a volume (approximately 6 Litres) of “warm water ready to go” as they say. The DHW production is always available and always in condensing operation, resulting in lower energy costs and bills.

combi heat exchanger; new lpg boiler ; inc vat; vat;


This design feature also reduces the chance of scale, something that older technology boilers that use a plate heat exchanger can suffer from. This is incredibly important in hard water areas– as our heat exchanger, with its high velocity and flexing in operation, reduces the ability for scale to build up, and prevents this happening ensuring a long life lpg combi with trouble free operation.

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Scale blocking the heat exchanger – older technology heat exchanger systems for DHW production


This unique and clever engineered solution for our heat exchanger system provides many advantages as opposed to the most popular brands of lpg combi boilers, when you compare Worcester Bosch, Vaillant etc that use a traditional plate heat exchanger system, for the domestic water. This why many consider our boiler the best lpg combi boiler on the market when looking for a new lpg boiler.

External Propane combi boilers

We also supply a range of external combination boilers, powered by propane, 24kw ,28kW or 34 kW output, same performance figures as our internal units. These units are fully weatherproofed, and manufactured to IPX5D standards.

External lpg combi boiler; easy installation

External lpg combi boiler

Lpg boiler

A lpg boiler works just like a natural gas or an oil boiler, just that it’s fuelled by liquid petroleum gas or LPG as it’s more commonly known. Whereas natural gas boilers use gas supplied by the main gas grid or mains supply as its also referred too. An Lpg boiler is using fuel supplied either via storage cylinders or a lpg bulk tank. Most lpg boilers, be they combination or system boilers they can be easily converted to mains gas (natural gas) via a simple conversion kit.

Liquid petroleum gas

LPG is an abbreviation for Liquefied Petroleum Gas, which is a mixture of gaseous hydrocarbons derived from natural gas and oil extraction (66 percent) as well as oil refining (34 percent). LPG is still a fossil fuel as such and hence not a true ‘clean’ energy source, but it is a very efficient fuel.

LPG does, however, release less CO2 per unit of energy than coal or oil. It emits 81% of the CO2 per kWh produced by oil, 70% of that of coal, and less than 50% of that emitted by coal-generated electricity distributed via the grid. (Source Wikipedia – LPG Gas )

The gas is a colourless odourless liquid when in its stored format. Often, for safety reasons an odorant is added to aid in the detection of any potential leaks.

Lpg cylinders supplying boilers lpg fired; vat; best lpg combi boiler

Lpg cylinders supplying boilers lpg fired


It is either stored in cylinders or a Lpg storage tank. There are pros and cons of each storage system, and the most popular is a lpg tank storage system, as they use a relatively small space, to store a large amount of the dense liquid form of lpg, which holds a lot of energy efficient fuel.

propane bulk tank; vat


These days a lpg storage tank comes with devices that monitor the quantity of gas in your tank and automatically inform your provider when it needs to be topped off. So, you never run out of fuel for your central heating system and to heat your hot water requirements.

Lpg combi boilers

The most common models of our huge range of lpg boilers are these –

24kW Lpg combi boiler

This lpg boiler is the smallest of our range of combination boilers. Even though the unit is called the 24kW – it will produce 24.79 kW of output when running at a 50/30°C flow and return temperature, as with all condensing boilers, the lower the return water under the dew point of the flue gases (generally 55C), the more efficient condensing boilers are.

Adversely if running at higher flow and return temperatures for the heating system, say 80/60C, then you’re not going to get the boiler to condense, and lose some energy efficiency, as it’s not recovering the heat from the flue gases. Thus at 80/60C our 24kW combi boiler will produce 22.7 kW of heating output – see the below technical data table for full details.

Our 24kW combination boiler is generally suitable for –

Apartments, flats and smaller 2 Bed houses, that have a maximum of 10 average sized radiators (these days the average radiator size is 1.5kW per rad on a new build) and that have one bathroom.

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24kW lpg combi boiler dimensions Flexiheat UK

This lpg boiler fit inside a standard kitchen cupboard, being small and compact as you can see from the above detail.

Fully modulating

This boiler is a fully modulating boiler, which means it varies its output to the heating system requirements, this results in a higher energy efficiency, and reduced energy bills. This also means you can’t really oversize the heating side of the lpg boiler as such, because it adapts to the heating system requirements of your flat, apartments or house. This modulation feature is common across all our range of lpg boilers and natural gas boilers.

This 24 kW lpg boiler will modulate down to 2.9 kW of output.

Making the DHW performance the most looked at element of the boiler –

These days , it’s the domestic hot water (DHW) performance of the boiler , that people usually select the unit on.

First typical flow rates of fixtures found in a property are –

A standard shower head has a hot water demand of 7 or 8 litres a minute

Bath mixer tap – a modern bath tap has an approximate flow rate of 12 Litres /minute

Basin / cloakroom (spray tap type) – 2 litres/minute

Sink taps (standard type) – 4 litres /minute –

So typical winter time performance for the 24kW boiler is 11.5 Litres/min

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R2C 24kW compact lpg combi boiler – technical data from Flexiheat UK


Download the full manual here for the 24kW version –

Flexiheat R2C 24kW Boiler Manual

28kW Lpg Combi Boiler

Same dimensions and features as our 24kW gas boilers, but with larger outputs – The 28kw designated model will produce 29.04 kW of max central heating output when running at a 50/30°C flow and return or 27.02 kW at 80/60C. It will modulate down to 3.5 kW of output.

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28kW Model dimensions


This 28 kW unit will produce 13.7 Litres of DHW at Δt 30°C

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R2C 28kW Combination lpg boiler DHW output data

Download the full manual here for the 28kW version –

Flexiheat R2C 28kW Boiler Manual

34kW lpg combi boiler

This 34kW combination boiler lpg fired, is slightly larger than previous units, it will produce 36.19 kW of output when running at a 50/30°C flow and return or 33.35 kW at 80/60C. It will modulate down to 4.1 kW of output.

34kw lpg combi boilers from Flexiheat UK;

34kw lpg combi boilers from Flexiheat UK

This 34kW model will produce 16 Litres of DHW at Δt 30°C

R2C 34kw technical output data

R2C 34kw model technical output data

Download the full manual here for the 34kW lpg boiler version –

Flexiheat R2C 34kW Boiler Manual


The standard warranty is for 2 years, but it goes up to 5 years on the heat exchanger if a heating system filter is fitted to the heating circuit to help maintain the efficiency and reliability of the system, which is now required as per the Part L building regulations requirements and also by BS 7593:2019, the code of practise for the preparation, commissioning, and maintenance of domestic heating and cooling water systems.


Our prices for our range of boiler white lpg fuelled units, which can be used on a standard radiator heating system, with normal radiators valves or thermostatic radiator valves or underfloor heating systems, with a manifold valve set up.

Propane LPG boiler

For more information or quotes on the best lpg combi boiler range for sale on the UK market, manufactured in high quality stainless steel, then please give our sales team a call on 01202 822221, or use the web site contact form.