A How to Guide on How to Repressurise an Ariston Boiler

When it comes to modern conveniences, having access to hot water is no longer a demand but a priority. If your Ariston boiler has stopped working and displays a 108 error, you must repressurise it.

It is normal to need to repressurise your boiler once a year. Most property owners can do this simple DIY job, or if you have an annual boiler service done by a Gas Safe registered engineer, you might not need to top up your boiler’s water level.

However, if your Ariston boiler needs to be repressurised on a regular basis, it could be an indication that there’s an underlying problem with your home’s unit.

Why Does Your Ariston Boiler Lose Pressure?

Pressure loss is common in all boilers, and Ariston is no exception. Here are some of the most common reasons:

1. A Leak In The System

Even a tiny leak in your heating system—whether in the pipes, radiators, or the boiler—can cause pressure loss. Signs of leaks include:

• Damp spots or water puddles.
• Inconsistent heating or hot water.
• Gurgling or hissing noises.
• A steady drop in pressure over time.

Leaks can occur in hidden areas such as walls, floors, or ceilings. If you suspect a leak, contact a Gas Safe-registered engineer to investigate and repair it.

2. Faulty Pressure Relief Valve (PRV)

The pressure relief valve is a critical safety feature that releases excess pressure to protect the system.

A malfunctioning PRV may leak water or fail to regulate pressure correctly, resulting in drops.

If the PRV is damaged, an engineer must replace it. If not repaired, a damaged PRV could cause serious problems.

3. Air In The System

Air trapped in your radiators can prevent efficient heating and cause pressure drops. This issue is typically resolved by bleeding the radiators.

However, over-bleeding can inadvertently lower the system’s pressure.

Another cause for air pockets developing in your system is not using enough inhibitors to stop elements within the system from rusting. When rust is created, the chemical reaction will produce bubbles forming into air pockets.

For homeowners who regularly top up their boiler systems, it is essential to pay attention to ensure that the levels of these inhibitors don’t drop too low; otherwise, you will create a lot of work in the future.

Ensure a Gas Safe registered engineer checks that your systems inhibitors are within the correct parameters.

4. Expansion Vessel Issues

Your boiler’s expansion vessel regulates pressure as the water heats and cools within a pressurised system. It deals with these natural contractions.

However, if the vessel’s internal diaphragm or air cushion fails, the system will struggle to maintain proper pressure.

A damaged expansion vessel must be repaired or replaced by a professional.

5. Freezing Temperatures

In winter, external condensate pipes can freeze, obstructing water flow and causing the boiler to lose pressure.

Symptoms of a frozen condensate pipe include no heating or hot water from the boiler and gurgling noises from the boiler.

Thawing the pipe with warm (not boiling) water can resolve this issue.

Now that we know the common potential problems let’s examine the ideal pressure for your Ariston Boiler.

What’s The Ideal Pressure For An Ariston Boiler?

The recommended pressure range for most Ariston boilers is between 1 and 1.5 bars. You can check the pressure on your boiler’s pressure gauge.

The needle should sit in the green zone.

However, we always recommend referring to your Ariston boiler’s manual.

Now, let’s start repressurising your Ariston Boiler.

Step-By-Step Guide To Repressurising An Ariston Boiler

It’s essential to stick to the steps for repressuring your Ariston Boiler. Let’s first complete step 1.

Step 1: Turn Off The Boiler

Switch off your Ariston boiler and let it cool for at least 4-6 hours. This ensures safety and prevents damage to the system.

If you can’t locate the off switch, we’d suggest turning off your boiler’s power supply from the circuit breaker box.

Step 2: Locate The Filling Loop

Ariston boilers will feature a filling loop to repressurise the system.

The filling loop is usually found beneath the boiler and can be either an:

• External (detachable braided hose) loop or
• Internal (built into the boiler) loop.

If it’s an external filling loop, ensure both ends are securely attached before proceeding.

Step 3: Open The Valves

You will want to open the valves in the same sequence for external and internal loops.

• Open the first valve to allow cold water into the loop.
• Gradually open the second valve, monitoring the pressure gauge as water flows into the system.

Be cautious not to overfill, and close the valves once the gauge reads between 1 and 1.5 bars.

Step 4: Close The Valves And Remove The Filling Loop (If Applicable)

After reaching the optimal pressure, close the valves in reverse order:

1. Close the valve feeding the boiler system.
2. Close the valve connecting to the mains water supply.

If using an external filling loop, detach and store it safely to prevent contamination.

Step 5: Turn The Boiler Back On

Switch your boiler back on and check the pressure again after a few minutes.

If the pressure rises above 1.5 bars, bleed the radiators to release excess water and bring the pressure down.

Step 6: Monitor The System

Keep an eye on the pressure over the next few days.

If you have more drops in pressure it will be a strong indication that it needs professional attention.

But who are you going to call?

WarmZilla That’s Who!

While repressurising an Ariston boiler is a straightforward task, recurring pressure loss signals a deeper issue.

You can always contact us for a Gas Safe registered engineer to visit your home within 48 hours – anywhere in the UK.

If you need to chat with a professional, we have an entire call center of them waiting to take your questions.