How to Top Up Baxi a Boiler

What Model Do I Have?

Baxi boilers typically use one of the following filling systems:

• Internal lever filling loop
• Internal tap filling loop
• External filling loop

Before topping up your boiler, it’s important to identify which filling loop you have, as the steps differ slightly for each type.

Baxi Boiler – Internal lever Filling Loop

(This is the newest version)

Many modern Baxi boilers use an internal lever filling loop, operated by a blue lever located underneath the boiler.

Step 1 – Access the Blue Filling Lever

Your boiler may have a decorative panel underneath, meaning you cannot immediately see the blue filling lever.

This panel is purely for appearance.
It is safe to remove and no harm will be done by taking it off.

The panel can be left off permanently if preferred.

Step 2 – Gently Pull the Blue Lever Down

Gently pull the blue lever down.

You should hear water running as the system begins to fill.
Go slowly — do not force the lever.

If needed, release the lever slightly and re-apply gentle pressure until you feel comfortable and confident with the movement.

Step 3 – Continue Filling While Watching the Pressure Gauge

Once you’re confident with Step 2, continue filling while keeping your eyes on the pressure gauge.

The pressure will begin to rise steadily as water enters the system.

Step 4 – Stop Just Over 1 Bar

Watch the gauge closely.
When the pressure reaches just over 1 bar, release the blue lever to stop the filling process.

That’s it — job done ✔️

Pressure Note

• Do not allow the pressure to exceed 1.5 bar

• Overfilling can damage the boiler and heating system

Baxi Boiler – Internal lever Filling Loop

(This is the newest version)

Many modern Baxi boilers use an internal lever filling loop, operated by a blue lever located underneath the boiler.

Step 1 – Access the Blue Filling Lever

Your boiler may have a decorative panel underneath, meaning you cannot immediately see the blue filling lever.

This panel is purely for appearance.
It is safe to remove and no harm will be done by taking it off.

The panel can be left off permanently if preferred.

Step 2 – Gently Pull the Blue Lever Down

Gently pull the blue lever down.

You should hear water running as the system begins to fill.
Go slowly — do not force the lever.

If needed, release the lever slightly and re-apply gentle pressure until you feel comfortable and confident with the movement.

Baxi Boiler – Internal Tap Type Filling Loop 

A common setup on Baxi boilers is an internal lever filling loop, usually operated by two small blue taps underneath the boiler.

Step 1

You can identify an external filling loop by locating two valves

🟦 Blue Flame Engineer Tip

Sometimes one of the blue taps underneath a Baxi boiler may already be left open.
If this is the case, you may only need to turn one tap to begin topping up the pressure.

This is very common and nothing to worry about.

Also note that the taps can be difficult to see when the boiler is installed low to the ground or inside a cupboard.
Using a torch or phone light can make them much easier to locate.

Step 2 – Open the First Valve (Door)

Slowly open either one of the blue levers — it does not matter which one you open first.

Think of this like “opening the first door”
At this stage, water is allowed to travel up to the second valve, but nothing will happen yet.

You may hear a faint sound of water, but the boiler pressure will not increase at this point.

Step 3 – Open the Second Valve (Door) VERY Slowly

Now, very slowly open the second blue lever.

This is the second door.
Once this door is opened, water is allowed into the boiler and heating system.

Open this valve a tiny amount only — do not open it fully.
You should hear water running, and the pressure on the gauge will begin to rise.

Move the lever gently, as if you are just cracking a door open, not swinging it wide.

Blue Flame Tip

Opening this valve too quickly can cause the pressure to rise too fast.

Step 4 (Be very careful here)

Keep a close watch on the pressure gauge.

Once the pressure reaches just over 1 bar (do not exceed 1.5bar), close both taps.

Safety note (See gauge)

Do not overfill the pressure past 1.5 bar.
Overfilling can damage the boiler and heating system.

Baxi Boiler – Internal Tap Type Filling Loop 

A common setup on Baxi boilers is an internal lever filling loop, usually operated by two small taps underneath the boiler.

Step 1

You can identify an external filling loop by locating two valves.

🟦 Blue Flame Engineer Tip

Sometimes one of the blue taps underneath a Baxi boiler may already be left open.
If this is the case, you may only need to turn one tap to begin topping up the pressure.

This is very common and nothing to worry about.

Also note that the taps can be difficult to see when the boiler is installed low to the ground or inside a cupboard.
Using a torch or phone light can make them much easier to locate.

Step 2 – Open the First Valve (Door)

Slowly open either one of the blue levers — it does not matter which one you open first.

Think of this like “opening the first door”
At this stage, water is allowed to travel up to the second valve, but nothing will happen yet.

You may hear a faint sound of water, but the boiler pressure will not increase at this point.

Step 3 – Open the Second Valve (Door) VERY Slowly

Now, very slowly open the second blue lever.

This is the second door.
Once this door is opened, water is allowed into the boiler and heating system.

Open this valve a tiny amount only — do not open it fully.
You should hear water running, and the pressure on the gauge will begin to rise.

Move the lever gently, as if you are just cracking a door open, not swinging it wide.

Blue Flame Tip

Opening this valve too quickly can cause the pressure to rise too fast.

Baxi Boiler – External Filling Loop 

A common setup on Baxi boilers is an external filling loop.

This is usually a silver braided hose connecting the mains cold water supply to the heating system pipework.

Step 1

You can identify an external filling loop by locating two valves:

Note: Some set-ups only have 1 lever – this is normal.

Step 2 – Open the First Valve (Door)

Slowly open either one of the black levers — it does not matter which one you open first.

Think of this like “opening the first door”
At this stage, water is allowed to travel up to the second valve, but nothing will happen yet.

You may hear a faint sound of water, but the boiler pressure will not increase at this point.

Step 3 – Open the Second Valve (Door) VERY Slowly

Now, very slowly open the second black lever.

This is the second door.
Once this door is opened, water is allowed into the boiler and heating system.

Open this valve a tiny amount only — do not open it fully.
You should hear water running, and the pressure on the gauge will begin to rise.

Move the lever gently, as if you are just cracking a door open, not swinging it wide.

Blue Flame Tip

Opening this valve too quickly can cause the pressure to rise too fast.

Step 4 (Be very careful here)

Keep a close watch on the pressure gauge.

Once the pressure reaches just over 1 bar (do not exceed 1.5bar), close both taps.

Safety note (See gauge)

Do not overfill the pressure past 1.5 bar.
Overfilling can damage the boiler and heating system.

Baxi Boiler – External Filling Loop 

A common setup on Baxi boilers is an external filling loop.

This is usually a silver braided hose connecting the mains cold water supply to the heating system pipework.

Step 1

You can identify an external filling loop by locating two valves.

Note:  Some set-ups only have 1 lever – this is normal

Step 2 – Open the First Valve (Door)

Slowly open either one of the black levers — it does not matter which one you open first.

Think of this like “opening the first door”
At this stage, water is allowed to travel up to the second valve, but nothing will happen yet.

You may hear a faint sound of water, but the boiler pressure will not increase at this point.

Step 3 – Open the Second Valve (Door) VERY Slowly

Now, very slowly open the second black lever.

This is the second door.
Once this door is opened, water is allowed into the boiler and heating system.

Open this valve a tiny amount only — do not open it fully.
You should hear water running, and the pressure on the gauge will begin to rise.

Move the lever gently, as if you are just cracking a door open, not swinging it wide.

Blue Flame Tip

Opening this valve too quickly can cause the pressure to rise too fast.