how to use a combi boiler

How to Use a Combi Boiler

Before we delve deeper into How to Use a Combi Boiler in the most efficient way possible, probably it would be a good idea to understand What is a Combi Boiler and How a Combi Boiler Works, for which we’ve done in-depth guides on our website previously.  Briefly, combi stands for combination, because the boiler combines heating and hot water into one compact unit, and eliminates the need for hot water storage in a cylinder or cold water in attic tanks.  The primary heat exchanger in a combi boiler heats water which heats the radiators in your home and comes back to the boiler.  This water then passes through a secondary plate heat exchanger which heats your drinking water in a sealed chamber.  In modern condensing boilers, the primary heat exchanger also condenses the water vapor to produce extra heat.

There are many energy efficient ways to get the best out of your combi boiler, some of which we’re going to discuss below:

How to Use a Combi Boiler with On-Demand Hot Water

how to use a combi boiler hot water

Combi boilers are perfect for properties with 1 bathroom, and may not be suitable for a property with 2 bathrooms.  However, that may depend on a couple of factors, and fortunately in 2018 there are a few more options for the consumer.  A combi boiler produces hot water on-demand, which means it heats and dispenses the water as and when you need it.  Which is why combi boilers are not suitable for larger homes where there may be a need for hot water from multiple taps simultaneously.  If that’s the case, you may need a larger capacity combi boiler i.e. 35kw, or a Storage Combi Boiler, or an Open Vent boiler or a Sealed System boiler.

Because there’s no hot water storage cylinders required with a combi boiler, hot water flow rates may not be as high as compared to a sealed system or an open vent boiler.  If you’ve got decent water pressure from the mains, the hot water pressure coming from your combi boiler should be fine too.  How to use a combi boiler with low mains pressure?  There are water pressure booster pumps available like the HomeBoost Mains Water Pump from Salamander.

How to use a combi boiler with on-demand hot water really depends on your needs.  So if you’ve got to take a hot shower urgently, it’s best to advice your other half to not wash the dishes at the same time!  If you’re filling a bath tub up, do not mix hot and cold taps.  Instead fill the tub up with the desired amount of hot water first, and then add cold water afterwards.  That’s because the hot water flow rate is lower with a combi boiler as it produces that hot water on-demand, compared to other types of boilers which store the hot water in a cylinder.

PLEASE NOTE:  Storing hot water in a cylinder may not be the most energy efficient solution.  A DHW (domestic hot water) storage cylinder is usually between 200 to 300 litres, and every time the water temperature goes down, it needs to start back up again to keep the water hot and ready for use.  Which is why a combi boiler may be more energy efficient because it only heats the water when you need it.

Endless Supply of Hot Water

Another advantage of combi boilers over regular boilers is of course, endless supply of hot water, because the hot water is available on-demand and instantaneously.  Whereas with hot water storage cylinders, once they empty, you have to wait for them to fill back up and heat again.

Check Your Pipes for Leaks

How to use a combi boiler to ensure maximum efficiency?  Periodical checks of your water pipes and taps for any leaks can help save you money not only on wasted water, but also on the overall efficiency of your central heating system along with the following.

Water Saving Showers instead of Baths

By replacing the taps and showers in your house with water saving options, you can not only save money on your water bills, but because you’re consuming less hot water, the combi boiler doesn’t have to work so hard, consumes lesser gas and electricity, thereby saving you money on your energy bills as well.  The same applies to using showers instead of baths, as with a shower you consume three times lesser hot water compared to a tub full of water.

Setting Heating Temperatures

how to use a combi boiler, heating controls

Ideal Temperature for Your Home

The optimal temperature for your home should be between 18°C – 21°C.  If you reduce the temperature in your home by even 1°C, you can save between 6% to 8% on your energy bills annually.  How to use a combi boiler to save money on your gas bills?  Next time you feel the room’s temperature getting a little chilly, put on a sweater and socks instead of cranking your thermostat up!  You’re not only saving money for yourself, but also reducing your overall carbon footprint and leaving a cleaner, more sustainable planet for future generations to come.

Operating instructions for a combi boiler may vary for different manufacturers, so it’s always best to refer to operating manuals or the manufacturer website for resources.

Old Analog Controls vs New Programmable Wireless Digital Thermostats

If you’ve already invested or are thinking about investing in a combi boiler replacement, it’s a good idea to upgrade to programmable thermostats to be compliant with Boiler Plus Legislation 2018 (in England, coming soon to Wales) for any new boiler installations.  We know a lot of people prefer the old analog dials on the wall, because they’re simple.  But those things are obsolete and won’t help you bring the overall energy efficiency of your home up.

How to use a combi boiler with programmable thermostats?  It’s pretty easy.  They help you program your boiler to only come on during certain times of the day, so that they’re not working all the time and using electricity and fuel constantly.  On first try, yes, they may seem difficult, but just like anything else in life, with consistent daily use you become better at it.  Practice makes perfect.

Setting Hot Water Temperatures

How to use a combi boiler to save energy with your hot water?  Operational instructions to set hot water temperatures will vary for different manufacturers, so we recommend looking at the operating manuals for your boiler or the manufacturer website for guides or videos.  For ex. if you have a Viessmann Vitodens 100-W boiler in your home, the video below should help:

Understanding Outputs in Boilers

Before you’ve bought a combi boiler, probably a better question than how to use a combi boiler, is how to find the right boiler for your property.  This post will help you out.  Residential boilers are available in a vast variety of outputs, anywhere from 13kW up to 40kW.  The larger the kilowatt, the better flow rates you get.  To calculate the kilowatt requirements of a central heating system for your property, the average figure is around 1.2 kW per radiator in your house.  So, if you have 11 radiators in your house, the boiler suitable to heat your house would be 11 x 1.2 = 13.2 kW minimum.  However because a combi boiler uses all of its capacity to heat water, a 29kW boiler will be a safe bet for your house.  If there are more than 1 bathroom in your house, a step up to 35kW would be sensible.

PLEASE NOTE: The figures given above are approximate figures.  For a more accurate calculation of your heating requirements, we’ve developed our intelligent quoting system over time, which will suggest boilers with the right output based on the answers you provide to its questions.  It’s pretty accurate.  To get a free, no obligation online boiler quote within minutes, just hit the green button below:

How to Use a Combi Boiler for a Larger Property


how to use a combi boiler, large property

A couple of years ago if your property was too large for the combi boilers available, your only other options were Open Vent Boilers (with attic tanks and hot water cylinder), or Sealed System Boilers (with a hot water cylinder).  Fortunately now we have storage combi boilers available, which are combi boilers with an integrated thermal store, so you save space and get unlimited hot water at mains pressure.  We have done an extensive post on the topic, click the following link to read it in its entirety: Storage Combi Boiler

High end storage combi boilers, like the Viessmann Vitodens 111-W and others have what’s called a CLS (cylinder loading system) which means there is no delay in refilling and heating the in-built thermal store like it would be with an external cylinder you normally see with an Open Vent or a Sealed System Boiler.

To find the best combi boiler suitable for your property, and to get free heating advice on combi boilers or a full new central heating system, please hit the green button below.  The online boiler quote is free, no-obligation and takes a couple of minutes:

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