Ariston Clas System One Boiler

The Ariston Clas System One is a high-efficiency boiler that boasts quiet operation and exceptional performance.

Ariston Clas System One

Available in three heat outputs, the Ariston Clas System One is Energy Saving Trust recommended and TUV Rheinland tested and certified. It comes with the new Xtratech heat exchanger, a load of advanced functions and a decent parts and labour warranty. The brand says that this system boiler is the most energy efficient ‘Clas’ boiler in the entire range, so it could be perfect for you if you’re looking to keep emissions low and significantly reduce your energy bills. 

How Much Does this Boiler Cost?

The cost will mainly depend on whether you need the 18kW, 24kW or 30kW Ariston Clas System One. Prices range from £775 to £1,125, so you just need to work out which heat output is right for your home and requirements. You also need to consider the fitting cost, which is usually anything between £1,500 and £1,800. It’s worth shopping around and getting a few quotes to see if you can save any money on the boiler and the installation.

How will I know if this Boiler is Suitable for My Home?

Ariston’s Clas System One comes in three outputs to suit the needs of small, medium and large homes. Because it’s a system boiler, it requires a separate hot water cylinder but the good news is that it doesn’t need a big loft tank. If you have more than one bathroom, the Clas System One will be able to provide a constant supply of hot water to multiple taps that are in use at the same time. And as an LPG conversion kit is supplied with the boiler as standard, it can be fitted in properties with or without access to mains gas. 

Be sure to check with your heating engineer which boiler type and size is best for you property prior to making a decision.

Is it a High Efficiency Boiler?

Itand has an A energy rating.  tywith or without access to mains gas. n on best for you property prior to water to multiple taps ‘s actually Ariston’s most energy efficient ‘Clas’ boiler and it has an A energy rating. Higher efficiency levels are achieved with a little help from the new Xtratech heat exchanger and the built-in Auto Function, both capable of improving boiler performance and efficiency. Also, the boiler is compatible with Ariston’s latest wired and wireless controls for further energy and cost savings.

Does this Boiler have a Good Range of Controls and Features?

Yes, the Ariston Clas System One has some rather impressive key features and a clear display with intuitive buttons. Among the best features is the Xtratech heat exchanger that can deliver consistent levels of heat whilst keeping emissions and energy bills low, as well as the Auto Function that allows the boiler to automatically choose the ideal heat output to optimise efficiency. The boiler also has a Comfort Mode to ensure you always get hot water on demand almost instantaneously. Furthermore, the Clas System One has a new and improved silencer and the latest soundproofing technology.

How long is the Warranty on this Boiler?

The Ariston Clas System One comes with a lengthy 8-year parts and labour warranty as standard. That’s a pretty decent warranty!

Summary of Important Information

  • Priced between £775 and £1,125
  • Heating output of 18kW, 24kW or 30kW
  • Dimensions of 745mm (H) x 400mm (W) x 331 (D)
  • Uses gas or LPG as its fuel source
  • A-rated for efficiency
  • 8-year warranty as standard

Pros and Cons

To be honest, we have nothing negative to say about this boiler, and it’s clear that Ariston has put a lot of thought into the end product. To view our full list of pros and cons, just look below.  


  • Ariston boilers have a good overall Which? score of 64%
  • Suited to small, medium and large-sized homes
  • Easy to install, use and service
  • Xtratech stainless steel heat exchanger – maximises longevity, reliability and efficiency
  • Auto Function – enhances boiler performance and aids energy efficiency
  • Comfort Function – boiler can deliver hot water almost instantaneously
  • Improved silencer and the latest soundproofing technology – quieter running
  • Provides maximum energy efficiency – reduce fuel bills and carbon emissions
  • Compatible with a range of Ariston controls – improves efficiency and performance
  • TUV Rheinland tested and certified – safety, quality and usability
  • Works with LPG if required – perfect for properties off the gas grid 
  • 8-year warranty


  • Ariston has an ‘average’ Trustpilot rating – correct at the time of writing in May 2019
  • Requires separate cylinder
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