If you have to increase your boiler pressure every day or every week and the pressure still drops, it is a sign that something is not right.

This is one of the problems people in South Wales experience with their boilers. There may be a solution, but it can also indicate an issue that needs to be fixed before a fault occurs.

In this guide, we will explain what can cause pressure drops, what you can safely check at home, and when you should call a boiler engineer.

Do not worry, a properly functioning boiler usually holds pressure for months. If your boiler pressure keeps dropping, it is most likely due to one of the following reasons.

What Boiler Pressure Should Be

For combi boilers, normal pressure when cold is between 1.0 and 1.5 bar. When the heating system is running and the water heats up, the pressure can rise slightly, usually around 1.8 to 2.0 bar. The exact pressure can vary depending on the boiler and heating system.

If you constantly have to add water to maintain the correct pressure, it means there is a water leak somewhere, even if you cannot see it.

Why Your Boiler Pressure Keeps Dropping

Leak in the Heating System

The most common reason for pressure loss is a leak. It does not have to be a large leak; even a small leak can cause pressure to drop over time.

You should check the following areas for leaks:

Radiator valves

Bleed valves at the top of radiators

Radiator joints

Pipe connections under sinks, behind toilets, and in cupboards

Ceilings under bathrooms

Look for white marks, rust stains, damp areas, or carpet lines near pipes.

Water is Being Released Through the Pressure Relief Valve

Your boiler has a valve called the Pressure Relief Valve. If the pressure gets too high, this valve releases some water to protect the boiler. Sometimes, after the valve opens, it may not fully close. As a result, it can continue to leak a small amount of water.

You can check this by looking at the copper pipe near the wall. If it is dripping or has marks, that is a sign.

Expansion Vessel Problems

The expansion vessel helps keep pressure stable when water heats up and expands. If it is not working properly or has lost air, the pressure may rise during heating and then drop again after the Pressure Relief Valve opens.

You may notice the following signs:

Pressure rises too high when heating is on

Pressure drops after the boiler cools down

Water dripping from the Pressure Relief Valve pipe

Boiler showing a fault code

This is usually a job for a boiler engineer, as the expansion vessel needs checking and repairing.

Leaks Inside the Boiler

Some leaks happen inside the boiler. You cannot see them. They may be in seals, valves, or other components. Because the leak is internal, you may not see any water.

Filling Loop Not Fully Closed

If the filling loop is not properly closed, it can cause unstable pressure. Make sure the valve is fully closed after topping up water.

Radiators Recently Bled

If you have recently bled your radiators, the pressure will drop. This is normal. You just need to top up the pressure again, and it should then remain stable. If the pressure continues to drop, it is not caused by bleeding.

Checks You Can Do Yourself

You can carry out the following checks yourself:

Take a photo of the pressure gauge or note the reading and check it twice a day for several days.

Check radiator valves with a tissue. If there is a leak, you will see it.

Check the Pressure Relief Valve pipe for drips or marks.

Look for damp areas or green or white deposits in cupboards and around pipes.

If you suspect a leak near the boiler or equipment, or you smell burning, turn off the boiler and have it inspected.

When to Call a Boiler Engineer

You should call a boiler engineer if:

The pressure constantly drops to zero

The boiler frequently stops or shows a low pressure error

You see water coming from the discharge pipe

Pressure fluctuates heavily while heating is on

You need to top up more than once a week

If you continue using the boiler while pressure is dropping, it can lead to further issues such as pump failure or corrosion inside the boiler.

Can I Still Use the Boiler if the Pressure Keeps Dropping

If the pressure is still within normal levels and you cannot see any leaks, you can continue using heating and hot water. However, you should not ignore the problem. If the issue is related to the expansion vessel or Pressure Relief Valve and you are constantly topping up water, it may be masking a fault. This can lead to bigger damage later.

The rule is: topping up once after a radiator bleed is normal. If you constantly have to add water, this is not normal de

If you have to increase your boiler pressure every day or every week and the pressure still drops, it is a sign that something is not right.

This is one of the problems people in South Wales experience with their boilers. There may be a solution, but it can also indicate an issue that needs to be fixed before a fault occurs.

In this guide, we will explain what can cause pressure drops, what you can safely check at home, and when you should call a boiler engineer.

Do not worry, a properly functioning boiler usually holds pressure for months. If your boiler pressure keeps dropping, it is most likely due to one of the following reasons.

What Boiler Pressure Should Be

For combi boilers, normal pressure when cold is between 1.0 and 1.5 bar. When the heating system is running and the water heats up, the pressure can rise slightly, usually around 1.8 to 2.0 bar. The exact pressure can vary depending on the boiler and heating system.

If you constantly have to add water to maintain the correct pressure, it means there is a water leak somewhere, even if you cannot see it.

Why Your Boiler Pressure Keeps Dropping

Leak in the Heating System

The most common reason for pressure loss is a leak. It does not have to be a large leak; even a small leak can cause pressure to drop over time.

You should check the following areas for leaks:

Radiator valves

Bleed valves at the top of radiators

Radiator joints

Pipe connections under sinks, behind toilets, and in cupboards

Ceilings under bathrooms

Look for white marks, rust stains, damp areas, or carpet lines near pipes.

Water is Being Released Through the Pressure Relief Valve

Your boiler has a valve called the Pressure Relief Valve. If the pressure gets too high, this valve releases some water to protect the boiler. Sometimes, after the valve opens, it may not fully close. As a result, it can continue to leak a small amount of water.

You can check this by looking at the copper pipe near the wall. If it is dripping or has marks, that is a sign.

Expansion Vessel Problems

The expansion vessel helps keep pressure stable when water heats up and expands. If it is not working properly or has lost air, the pressure may rise during heating and then drop again after the Pressure Relief Valve opens.

You may notice the following signs:

Pressure rises too high when heating is on

Pressure drops after the boiler cools down

Water dripping from the Pressure Relief Valve pipe

Boiler showing a fault code

This is usually a job for a boiler engineer, as the expansion vessel needs checking and repairing.

Leaks Inside the Boiler

Some leaks happen inside the boiler. You cannot see them. They may be in seals, valves, or other components. Because the leak is internal, you may not see any water.

Filling Loop Not Fully Closed

If the filling loop is not properly closed, it can cause unstable pressure. Make sure the valve is fully closed after topping up water.

Radiators Recently Bled

If you have recently bled your radiators, the pressure will drop. This is normal. You just need to top up the pressure again, and it should then remain stable. If the pressure continues to drop, it is not caused by bleeding.

Checks You Can Do Yourself

You can carry out the following checks yourself:

Take a photo of the pressure gauge or note the reading and check it twice a day for several days.

Check radiator valves with a tissue. If there is a leak, you will see it.

Check the Pressure Relief Valve pipe for drips or marks.

Look for damp areas or green or white deposits in cupboards and around pipes.

If you suspect a leak near the boiler or equipment, or you smell burning, turn off the boiler and have it inspected.

When to Call a Boiler Engineer

You should call a boiler engineer if:

The pressure constantly drops to zero

The boiler frequently stops or shows a low pressure error

You see water coming from the discharge pipe

Pressure fluctuates heavily while heating is on

You need to top up more than once a week

If you continue using the boiler while pressure is dropping, it can lead to further issues such as pump failure or corrosion inside the boiler.

Can I Still Use the Boiler if the Pressure Keeps Dropping

If the pressure is still within normal levels and you cannot see any leaks, you can continue using heating and hot water. However, you should not ignore the problem. If the issue is related to the expansion vessel or Pressure Relief Valve and you are constantly topping up water, it may be masking a fault. This can lead to bigger damage later.

The rule is: topping up once after a radiator bleed is normal. If you constantly have to add water, this is not normal de