Lpg combi boiler

Lpg Combi Boiler

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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.

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 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 does a lpg boiler work? quiet simply the same as a natural gas one – except the key difference – its fuel is LPG rather than natural.

Combi LPG boiler

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, and the flow of water they can heat is related to the power output of the 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 lpg combi boilers 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 lpg combi boiler. This also reduces carbon footprint as well, when compared to an older non condensing lpg boiler or oil boiler that aren’t condensing in function.

Our condensing lpg combi boilers achieve efficiencies of 105%, with many benefits such as a lower noise output than the majority of the gas boilers on the UK market, and a patented boiler exchanger, which is a pipe in pipe design.

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.

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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

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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, such as Worcester Bosch, Vaillant etc that use a traditional plate heat exchanger system, for the domestic water.


External lpg 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

External lpg combi boiler

Lpg boilers

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

Liquid petroleum gas – LPG

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.

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;

Lpg cylinders supplying boilers lpg fired


It is either stored in cylinders or a Lpg storage tank. There are pros and cons of each gas 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.

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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 its 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 performace the most looked at element of the boiler –

These days , it’s the domestic hot water (DHW) perofmance 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 boilers 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 Combi Boiler Manual

28kW Lpg Combi Boiler

Same dimensions and features as our 24kW model, but with larger outputs – The 28kw designated model will produce 29.04 kW of 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 Combi Boiler Manual

34kW lpg combi boiler

This 34kW model, 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 version –

Flexiheat R2C 34kW Combi Boiler Manual

Propane combi boilers

For more information 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.