Why Does the Combi Boiler Pressure Drop
Why Does the Combi Boiler Pressure Drop

Why Does the Combi Boiler Pressure Drop ?

Why Does the Combi Boiler Pressure Drop ? Combi boilers are devices that can meet the needs by giving hot water and that provide heat by sending heat to the honeycombs in cold weather. Like all electronic devices, problems with combi boilers are a fact of life.

Boiler Pressure Drop ?

Why Does the Combi Boiler Pressure Drop ? One of the most common problems is the decrease in boiler water pressure. In such cases, what to do when the boiler water pressure drops? How to increase the boiler water pressure? Why does the boiler water pressure drop? Why does the boiler water decrease? We start asking questions such as, and look for solutions.

If the Combi Water Pressure Drops Every 2-3 Months

While it is normal for the boiler water level to drop every few months, a frequent drop indicates that there is a problem. It is normal for the boiler to lose water every few months. Of course, if this change is at a value of 0.5 bar, it is normal. In this case, water can be added to the combi again with a small valve located under the combi.

There is an electronic or analog bar indicator on the combi, which shows the value of the water in the combi. This indicator is ideal between 1.5-2 bar. Service personnel coming for the boiler assembly say that the bar level should be at 1.5 bar.

Why is Combi Flooding Necessary?

The working logic of combi boilers is that the water in the combi is heated by passing through the heat exchanger and sent to the system. When the water in the combi boiler is below 1.5 bar, the combi pump works harder to provide circulation and increases the natural gas consumption and not enough efficiency from heating.

Why is the Combi Water Loss?

  • If the water shortage in the combi occurs every 2-3 months, it is normal and normal.
  • In this case, the small valve under the combi boiler opens and the bar level is restored.
  • If the water pressure drops frequently in the combi, it means there is a problem.
  • This is a situation that changes according to the frequency of the pressure drop.
  • If there is a daily drop, it may mean that there is a small crack in the heat exchanger. This is difficult to notice because the water coming out of the crack evaporates.
  • If the pressure drop is more frequent, then there may be a water leak somewhere in the plumbing system.
  • Even if there is a small crack in the installation, the boiler water pressure drops.
  • We cannot notice this because the pressure in the heating system is much lower than the fresh water pressure.
  • The only way to notice is if the bar indicator on the combi boiler goes down.
  • In this case, there is nothing you can do on your own.
  • We find the source of the problem with the thermal camera, report it and present it to you.

How do I check if my boiler pressure is low?

Why Does the Combi Boiler Pressure Drop ? If you suspect that your boiler has lost pressure, find your boiler manual and check the front panel on your boiler. Your boiler will have a pressure gauge that indicates whether the pressure is high, adequate or low. Modern boilers will often also have a screen which flashes an error code to indicate the cause of the problem. Check in your boiler manual to see whether the error code for your model corresponds with low boiler pressure.

The pressure gauge will show certain bars that indicate the levels of boiler pressure. If the boiler pressure needed or digital indicator is below one bar this means that your boiler has lost pressure. If the pressure bar is marked as high according to your user manual, then the pressure has increased above normal operating levels and can be lessened by bleeding the connected radiators. Your appliance or system has a built in safety device which automatically releases pressure preventing the pressure becoming dangerous. However, you should still bleed your radiators if the pressure is showing as too high.

What causes a boiler to lose pressure?

The most common reasons for a boiler to lose pressure are:

  • Releasing air or water from a radiator when bleeding it.
  • A leak from the appliance or on the system most commonly from radiator valves or system components.

The circuit of pipes and radiators connected to the boiler system can corrode or loosen over time, eventually allowing water to escape the system and gradually decrease the boiler pressure as water is replaced with air.

How do I find a leak in my heating system?

Although a leak can happen throughout the circuit of pipes and radiators inside the walls, it will most likely be found around the connections on radiators. Try to find signs of damp patches around the radiators. The pipework can become wet due to condensation rather than a leak, so make sure to carefully wipe the pipe clean and place a plate underneath it to check for any drips.Also check for discoloured paint or flaking on both the pipework and skirting boards, as well as water stains on the floor or ceiling. These are signs of water damage caused by leaks. Do not attempt to repair loose or broken pipework joints unless you are trained to do so. Instead arrange for a specialist to make the necessary repairs and check to see if the boiler stops losing pressure as a result.

Can a boiler lose pressure without a leak?

If you have found no leaks and your boiler is still losing pressure, the cause may instead be a boiler leak, a hidden leak on the system.

Boiler leak

Boiler leaks can occur when parts inside the boiler corrode or loosen over time. Unless a boiler is regularly serviced, boiler parts can loosen with age and cause the system to lose pressure, usually these leaks will be a visible drip from the underside of the boiler. If you suspect that a boiler leak is at fault, arrange for a Gas Safe Registered (GSR) boiler engineer to inspect your boiler. Do not remove the boiler casing yourself.They will then advise you on whether the part can be repaired or replaced, or if the entire system needs cleaning or replacing. Check to see whether your boiler is under warranty, as this could potentially save you hundreds of pounds in repair costs.

Faulty boiler part

Boiler parts can also simply become faulty over time and cause boiler heating problems. As above, do not attempt to identify the faulty boiler part yourself. Instead, call a GSR engineer to remove the boiler casing and identify the part for you. They will then let you know what needs to be repaired or replaced.

How do I fix low boiler pressure?

While fixing the leak or faulty boiler part issue is the long-term solution, you can also increase the boiler pressure yourself using the filling loop attached to your boiler. This is typically silver with a flexible connection, with a handle valve and an isolation valve on each end of a flexible pipe connection.Using a flat head screwdriver, turn the isolation valve anti-clockwise until the line on the valve is in line with the pipe. Then turn the handle valve anti-clockwise to allow water to enter the system. Monitor the pressure gauge to ensure that the pressure increases to the recommended levels, before closing both the handle valve and the isolation valve by turning them clockwise.You will know that the boiler pressure is back at recommended levels because either:

  • The fault code has disappeared
  • Or the boiler is functioning and heating water

If you are uncertain about how to top up the system pressure of your boiler, do not hesitate to ask a family friend, neighbour for assistance as topping up the pressure is common knowledge among many homeowners. If no one is available to assist you consulting a competent person or gas safe engineer is another option but is likely to be chargeable.


  • You can check if your boiler pressure is low by checking the pressure gauge and consulting the boiler manual.
  • Check for leaks around radiator pipe connections. Common clues include water stains and paint discolouration on pipes and skirting boards.
  • Call a qualified engineer to inspect your boiler if you suspect an internal part is at fault.
  • Familiarising yourself with the topping up procedure could prevent your boiler from failing to operate buying you valuable time until a Gas Safe Engineer can inspect your appliance or system.

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