Ariston boilers
Ariston is an Italian brand. Its story starts in 1930, when Aristide Merloni set up a company in the Marche region of Italy. At first it made weighing scales. The Ariston brand came in 1960, with electric water heaters. It started making boilers in the 1980s.
Today Ariston is part of the Ariston Group. The same group owns Vokera, another boiler brand you’ll see in UK homes.
The Ariston range
Ariston’s current gas boilers all have One in the name.
- Alteas One+ Net and Genus One+ WiFi are the higher-spec combis.
- Clas One is the everyday combi.
- Clas System One and E-System One are system boilers, for homes with a hot water cylinder.
- Clas One R is the regular boiler, for homes with tanks in the loft.
Older Ariston boilers may have names without “One”. The user manual will tell you which codes your boiler uses.
How Ariston boilers show a fault
Ariston boilers show a number on the screen when they stop. The Clas One manual explains two kinds of stop.
A safety shut-off is temporary. The code flashes, and the boiler starts again by itself once the problem has gone. If it doesn’t, Ariston says to switch the boiler off, turn off the gas valve and call an engineer.
Some faults need you to press the reset button. Ariston limits this to 5 resets in 15 minutes. That stops a faulty boiler being restarted again and again. If you need to reset it often, something is wrong. Call a Gas Safe engineer.
Code 108 and low pressure
The code you’re most likely to see is 108. It means the water pressure in the heating system is too low. You can usually fix it by topping up with the filling loop. If you have to do it often, there may be a leak. Ariston says to switch off and get an engineer to check.
The Clas One manual gives a different range from most makers. It says the gauge should read 0.6 to 1.5 bar when the system is cold. Other Ariston boilers may differ, so check your own manual. Our guide explains how to top up low boiler pressure.
Finding your Ariston manual
Ariston puts its user manuals on each boiler’s page, and on its downloads page. You’ll need the model name from the front of the boiler. If you can’t find it, see how to find your boiler’s model and GC number.
Cold weather
The Clas One has an anti-frost device to protect the boiler itself. But the condensate pipe outside can still freeze. If your boiler stops on a freezing morning, check that pipe first. Here’s how to thaw a frozen condensate pipe.
Ariston gas boiler ranges
These are the gas boiler ranges on the Ariston website as of 21/10/2026.
- Alteas One+ Net Combi
- Genus One+ WiFi Combi
- Clas One Combi
- Clas System One System
- E-System One System
- Clas One R Regular
Common Ariston fault codes
Codes can differ between models and ages of boiler. Always check the user manual for your exact model.
| Code | What it means | What you can do |
|---|---|---|
108 | The water pressure in the heating system is too low. The boiler has stopped for safety. | Top up with the filling loop. If it keeps happening, switch off and call a Gas Safe engineer to check for leaks. |
Ariston manuals
Ariston puts its user guides and installation manuals on its own website. You can find Ariston manuals here. You'll need your model name. The GC number helps too. Our guide shows you how to find your boiler's model and GC number.
Stay safe. You can reset a boiler, top up its pressure and thaw a frozen condensate pipe yourself. Anything inside the case is a job for a Gas Safe registered engineer.
If you smell gas, leave the building and call 0800 111 999.