A How To Guide On How To Repressurise A Vaillant Boiler

Nothing is worse than finding your Vaillant boiler has shut off, leaving you without heating or hot water.

If your Vaillant boiler displays the F22 fault code, it’s likely due to low system pressure.

To confirm that your Vaillant boiler needs to be repressurised, the pressure gauge in the right-hand corner of the LCD screen will flash zero to indicate that it needs a top-up.

To restore the correct pressure level, you’ll need to repressurise your boiler. This straightforward DIY task is manageable for most homeowners.

Repressurising your boiler has been designed to be as simple as possible, as many modern boilers require repressurising about once a year.

However, 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.

As mentioned, the F22 error code and flashing zero on the pressure gauge indicate that your Vaillant boiler’s pressure is low.

However, boiler pressure can drop for various reasons, and if you need to top up the water levels frequently, it may be time to call a Gas Safe registered engineer for a closer inspection.

But what are the common reasons a Vaillant boiler will lose its pressure more frequently?

What Can Cause A Vaillant Boiler To Lose Pressure Frequently?

There are several reasons why a Vaillant boiler would lose its water pressure frequently. But there are several common causes, which include the following:

Leak In The System

Even a tiny leak can cause a significant pressure drop, potentially shutting down your boiler.

For example, a drop in pressure from 1.5 to 0.5 bars indicates a loss of roughly three litres of water. To lose three litres in a week, the system would only need to leak at 17ml per hour, which is slightly more water than a single tablespoon (15ml).

Detecting these leaks can be challenging, as they may occur in hidden areas such as behind walls, under floors, or within ceilings.

However, there are common signs of a leak in your heating system:

• Visible water stains or damp patches
• Irregular heating or inconsistent hot water
• Strange noises like gurgling or hissing
• Unexplained spikes in water usage
• Unusual odours, such as dampness or a metallic smell

For hard-to-find leaks, a Gas Safe registered engineer can thoroughly inspect your heating system and pinpoint the issue.

Insufficient Inhibitors In Your Boiler System

Your boiler relies on inhibitors to slow down chemical reactions that can lead to blockages.

Without these inhibitors, these reactions will continue without slowing down and can cause sludge buildup, lowering the system’s pressure.

One common issue is the reaction between water and the metal components of radiators, which leads to rust formation. This chemical reaction creates rust particles and air bubbles, both of which can create blockages in the heating system.

However, air bubbles trapped in the radiators can disrupt water circulation and cause uneven heating. To solve this issue, you need to bleed your radiators, a simple DIY task that can release these air pockets and restore proper water flow, helping to stabilise pressure levels.

Also, if you frequently top up your boiler’s water levels, the system’s inhibitors can become diluted, increasing the likelihood of sludge buildup and pressure drops. Over time, this creates an environment where these issues escalate more quickly.

Contact a Gas Safe registered engineer if you think your heating system has lost its balance of inhibitors.

Bleeding Radiators: Avoiding Common Mistakes

Bleeding your radiators is a simple task, as we’ve mentioned. Cold spots at the top of your radiators are a telltale sign of air pockets in your heating system. If you’ve found cold spots at the top of your radiator, it’s time to bleed them.

But mistakes can happen when performing the easiest of tasks. If the valve is opened too far or left open too long, excess water can escape from the system, causing a drop in boiler pressure.

To avoid this:

• Open the valve slowly and gradually to release air bubbles without losing too much water.
• Monitor the system’s pressure gauge as you work.

If you accidentally let out too much water, you’ll need to repressurise your boiler to restore the correct pressure level.

Boiler Pump Issues

Your boiler’s pump is crucial in circulating water throughout your heating system and maintaining stable pressure. If the pump is set too high, it can cause turbulence in the system, leading to air bubbles and air pockets, which, as discussed, will cause issues.

An incorrectly set or malfunctioning pump cannot maintain pressure within your heating system. Common signs of a faulty pump include:

• The pump feels excessively hot to the touch.
• Water is leaking from the pump.
• Cold water is circulating instead of hot.

During your boiler’s annual service, a Gas Safe registered engineer will check and adjust the pump’s settings as needed.

However, If the pump is damaged, it will need to be replaced.

Expansion Vessel Issues

Your home’s boiler is a closed, pressurised system designed to circulate warm water. All materials will expand and contract when exposed to heat and allowed to cool off.

To accommodate the natural expansion and contraction caused by temperature changes, your heating system relies on the expansion vessel to regulate pressure fluctuations.

The expansion vessel features a tank with a rubber diaphragm and an air cushion that work together to maintain balance:

• When water heats and expands, the diaphragm compresses toward the air cushion to absorb the increased pressure.
• When the water cools and contracts, The diaphragm returns to its original position, ensuring consistent pressure within the system.

This mechanism prevents sudden pressure spikes that could damage your boiler or heating components.

If the expansion vessel becomes faulty, damaged, or loses its air charge, it will no longer effectively maintain the system’s pressure, resulting in a drop in pressure.

Only a Gas Safe-registered engineer can repair or replace an expansion vessel.

Chilly Weather and Frozen Condensate Pipes

During extended periods of freezing temperatures, the external condensate pipe on your Vaillant boiler may freeze. A frozen condensate pipe can prevent the boiler from operating safely, triggering specific error codes as a precautionary measure:

• Error Code F28: Indicates that the boiler’s ignition has failed after multiple attempts.
• Error Code F29: This means the flame has been extinguished after ignition.

These safety features are crucial, as operating the boiler without a clear path for condensate disposal could lead to hazardous conditions.

If your Vaillant boiler has a frozen condensate pipe, you may notice:

• Unusual gurgling sounds coming from the boiler.
• Water dripping or pooling beneath the unit.
• The boiler shuts down unexpectedly.
• There is no heating or hot water despite the boiler attempting to start.

To resolve this issue, the condensate pipe should be safely thawed by applying warm water (not boiling) or a heated cloth to the affected area.

Now that we’ve covered these common issues let’s explore the optimal pressure level for your Valliant boiler.

What Is The Best Pressure Level For A Vaillant Boiler?

The best pressure level for most boilers in the UK is between 1 and 1.5 bars — sometimes up to 2 bars when operational.

However, make sure that the pressure level doesn’t exceed 3 bars. Otherwise, you will need to bleed your radiators.

Vaillant boilers’ pressure gauges are located on the LCD in the right-hand corner of the screen. If the pressure gauge flashes zero, it clearly indicates that water needs to be added.

Vaillant recommends maintaining the pressure in its boilers between 1.0 and 2.0 bars when the heating is on and between 1.0 and 1.5 bars when the heating is off.

However, always refer to your boiler’s manual to confirm the recommended pressure levels, as there can be variations even between manufacturer models.

Now that we’ve discussed the best pressure for a Vaillant Boiler, let’s go through the step-by-step process of repressuring it.

Step-by-Step Guide to Repressurising Your Vaillant Boiler

Repressurising a Vaillant boiler, or any boiler, is a simple task. But, this being said, it’s essential to follow the steps carefully to ensure safety and proper operation.

Step 1: Turn Off the Boiler

Before starting, switch off your boiler’s power to prevent potential damage to the system. Also, it is a safety risk to work on an operating boiler.

Make sure to:

• Locate the fused spur switch (a square switch often near the boiler) and turn it off.
• If you can’t find the switch, check if the boiler is plugged into a standard household socket and unplug it.
• When unsure, turn off the home’s switchboard supply to it.

Some manufacturers recommend letting the boiler cool for 4–6 hours before repressurising to avoid handling hot components.

Step 2: Identify And Locate The Filling Loop System And Repressurise!

A boiler’s filling loop system connects the unit to your home’s cold water mains. It is used to top up the water levels in your boiler’s heating system.

The filling loop is typically found beneath the boiler and comes in two types: external and internal.

While they differ in design, both perform the same function.

External Filling Loop

An external filling loop is usually a braided metal hose that links the main cold water supply to the central heating system. These loops are often stored near the boiler.

An external filling loop has two valves:

1. Water Flow Valve — Controls the flow of water from the mains.
2. Backflow Prevention Valve — Stops water from the heating system from flowing back into the mains.

Depending on the design, you may need a flat-head screwdriver to operate the valves. In some cases, levers, additional keys, or tools might be required instead.

Also, before filling the external filling loop, ensure it doesn’t leak.

Using an external filling loop is a bit more complicated than repressurising a Vaillent’s ecoTEC range.

Usually, to attach an external filling loop, you need to perform the following steps:

• Unscrew the blanking caps on the connection points to expose the threads. Keep the caps in a safe place for reattachment later.
• Align the ends of the braided metal filling loop with the two connection points.
• Carefully screw the loop onto both connections, ensuring the washers inside the fittings are correctly seated to prevent leaks.
• Hand-tighten the connections and ensure they are secure, but avoid over-tightening, which could damage the threads or washers.
• Open the first valve, followed by the second valve. Open the second valve slowly and monitor the boiler’s pressure gauge.
• When the boiler reaches a pressure reading between 1.2 to 1.5 bars, close the second valve, followed by the first valve.
• Once you’ve repressurised your boiler, remove the external filling loop. Leaving it attached can increase the risk of contamination.
• Finally, have a towel handy, as there might be some extra water in the filling loop.
• Place blank caps back onto the thread points.

And just like that, you’re ready to go. Be aware that your boiler might perform a shutdown sequence that will take a few minutes.

Internal Filling Loop

An internal filling loop is integrated into the boiler and is usually standard in modern systems. It is more convenient as it remains permanently installed and is easier to use.

Some internal filling loops may require a key for operation, while others use lever taps.

Vaillent’s ecoTEC Plus models use an internal filling loop system (or a built-in filling loop).

Like an external loop, there are two valves, which are labelled and should read closed. Open the first valve, which is connected to cold water mains. Simply turn the valve’s tap to align with the pipe.

Before you open the second valve, ensure you can clearly read the boiler’s pressure gauge. When ready, gradually open the second tap.

You should hear the water entering the boiler and the pressure gauge rising. When the gauge reaches 1.2 and 1.5 bars, turn off the second valve, followed by the first valve you opened.

When you close the first valve, the Vallient ecoTEC Plus automatically performs a shutdown sequence and is ready to use within 10 minutes.

If you accidentally overfilled your Vaillent boiler, you’ll need to bleed your radiators to bring the pressure back to the correct level. As mentioned earlier, this is a straightforward task.

However, if you’d rather not take on another DIY project, you can always seek assistance from a professional.

Call WarmZilla To Help You

While learning a new skill is admirable, sometimes time constraints or the need for precision make it better to rely on a professional.

WarmZilla provides emergency boiler repair services within 48 hours across the UK.

Our team of experts is here to help. Contact us for advice on your next steps or to schedule a professional visit.