- Boilers
- Gas boiler
108
Ariston 108 on a gas boiler: water pressure too low
Risk level
Medium
Proceed carefully and stop if the check is unclear.
Urgency
Medium
Quick answer
Ariston 108 means water pressure in the heating circuit is too low. Open the filling valve under the boiler and close it when the gauge reads between 1 and 1.5 bar. If it keeps happening, switch off, close the gas and call a technician.
Safety first
Stop and check this first
- If you smell gas: Ariston says to close the main gas tap, open the windows and call the technician. Do not operate switches or light flames, leave the home and call your gas distributor's emergency number from outside. If you smell burning or see smoke, cut the power, close the gas and ventilate.
- If you have to top up often, Ariston says to switch the boiler off, set the external switch to OFF, close the gas and call a technician to look for leaks. Always close the filling valve afterwards.
Safe checks you can perform
- Gauge pressure
- Top up with the filling valve
- Visible leaks
- Leak search by the technician
Leave these tasks to a qualified professional
- Do not attempt this professional task: Boiler pressure reading check
- Do not attempt this professional task: Pressure drop test
What a technician must be able to justify
Technician visit
These are the steps they must carry out and show you. Tick them as they work: if steps are skipped, do not accept a part swap.
These are not instructions for opening or handling the equipment yourself. They are the checks that should support a technical conclusion.
Boiler pressure reading check
What they doIf pressure is correct and the code stays, the technician checks the boiler's pressure reading and its connection.
They must show youthe gauge reading against the boiler's reading.
In writingany part replaced and why.
Pressure drop test
What they doThe technician leaves the system at rest, checks with a gauge whether pressure falls and looks for the leak.
They must show youthe pressure at the start and end of the test.
In writingwhere the leak was and what was repaired.
Before accepting a part or repair
Nothing has been shown yet. Do not accept a part swap based on the code alone.
Follow these steps
Note: Follow the documented order. An error code identifies the affected system, but it does not prove by itself which part has failed.
Gauge pressure
- Who:
- you.
- How:
- look at the boiler's pressure gauge and whether the display asks you to fill the system.
- Result that matters:
- whether pressure is below 1 bar.
- If it is low:
- top up as Ariston describes in the next check.
- If the pressure is right and 108 stays:
- do not add more and call the technician.
- Evidence to keep:
- a photo of the gauge and the display.
Evidence: Calderas Ariston: significados de los códigos de error · Ariston CLAS One System, manual de usuario
Top up with the filling valve
- Who:
- you.
- How:
- open the filling valve at the bottom of the boiler; on the Clas One also press MODE for 5 seconds until PURGE appears, as the manual says. Close the valve when the gauge reads between 1 and 1.5 bar and press MODE again.
- Result that matters:
- whether the pressure rises and holds and 108 clears.
- If the pressure holds:
- it was lack of water; note the date.
- If it drops again soon:
- water is being lost; do not keep topping up.
- Evidence to keep:
- photos of the gauge before and after and the date of each top up.
Evidence: Calderas Ariston: significados de los códigos de error · Ariston CLAS One System, manual de usuario
Visible leaks
- Who:
- you.
- How:
- look under the boiler, radiators and valves for water, stains or drips, without taking anything apart.
- Result that matters:
- whether there is a visible leak.
- If you see water or drips:
- switch the boiler off, close the gas and call a technician, as Ariston says if the problem repeats.
- If everything is dry and the pressure holds:
- the cause was lack of water.
- Evidence to keep:
- photos of stains or drips.
Evidence: Calderas Ariston: significados de los códigos de error · Ariston CLAS One System, manual de usuario
Leak search by the technician
- Who:
- qualified technician.
- How:
- looks for water leaks in the boiler and system and checks its pressure components.
- Result that matters:
- where the water is going.
- If the leak is found:
- it is repaired and the pressure stops dropping.
- If there is no leak and 108 stays with correct pressure:
- the boiler's pressure reading is checked.
- Evidence to keep:
- a report of what was checked and repaired.
Ariston reserves repairs for its official service centre or a qualified technician: opening the boiler is not the user's job.
Evidence: Calderas Ariston: significados de los códigos de error · Ariston CLAS One System, manual de usuario
Still not solved
If the error persists, stop here. See what the technician must do and show you.
Where this code applies
A code is meaningful only inside the right product and version context.
Primary scope
- System
- Boilers
- Brand
- Ariston
- Product type
- Gas boiler
Known code variants
- 1 08
- Ariston 1 08
- Ariston E108
- Chaffoteaux 1 08
- Clas One 108
- Error 108 Ariston
- Error 108 Chaffoteaux
- Pigma 108
What it means
In the Clas One table, 1 08 is system filling, in the primary circuit group; Ariston explains the boiler locks because water pressure in the heating circuit is too low, and the display may ask you to fill the system. Ariston gives leaks in the system or lack of filling as causes. The code watches circuit pressure; it does not locate where the water is lost.
Warnings and stop conditions
- Criticaleditorial warning
If you smell gas: Ariston says to close the main gas tap, open the windows and call the technician. Do not operate switches or light flames, leave the home and call your gas distributor's emergency number from outside. If you smell burning or see smoke, cut the power, close the gas and ventilate.
Evidence: Ariston CLAS One System, manual de usuario
- Mediumsource verified
If you have to top up often, Ariston says to switch the boiler off, set the external switch to OFF, close the gas and call a technician to look for leaks. Always close the filling valve afterwards.
Evidence: Calderas Ariston: significados de los códigos de error · Ariston CLAS One System, manual de usuario
Symptoms and causes
Probable causes · in order
- Not enough waterCommon
Ariston lists it as a cause. If after topping up the pressure holds for weeks, that was it and not a fault.
Evidence: Calderas Ariston: significados de los códigos de error
- Leak in the systemPossible
Ariston lists leaks. If you have to top up often, water is escaping from radiators, pipes or the boiler itself; Ariston then asks for a technician to look for leaks.
Evidence: Calderas Ariston: significados de los códigos de error · Ariston CLAS One System, manual de usuario
Virtual technician
Does 108 still appear after these checks?
Answer a few questions to narrow down the likely cause and the safest next action. Guidance only - it never replaces a professional.
Sources and technical references
- 1
Calderas Ariston: significados de los códigos de error
Ariston · 2025 · official_doc
- 3
Ariston CLAS One System, manual de usuario
Ariston · 2017 · manual
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