Why is my Boiler Losing Pressure but I can’t Find a Leak?

It’s almost inevitable that your boiler is going to have a problem sooner or later, the most common issue is having low water pressure. If this is the case for you, this guide should help you be on your way with a fixed, working boiler in no time.

What does an Expansion vessel do?

When water is heated up it expands in size by approximately 4%. This expansion has to go somewhere. On a combi boiler, it has an expansion vessel to take up this expansion of water.

When the expansion vessel is faulty it will cause a rise in pressure when your boiler is heating up your radiators.

What is an expansion vessel?

An expansion vessel is a steel vessel within the boiler. Inside the vessel is a rubber diaphragm with your central heating system water on 1 side and air (sometimes nitrogen) on the other side.

How does the expansion vessel work?

The expansion vessel works in the following way. When the water is heated through your boiler when your heating is on it will start to expand within your radiators, pipework and boiler. That expansion has to go somewhere, so it expands into the space that is occupied by the air in the expansion vessel. The air compresses in the vessel. As the water cools down the air pushes back into its normal space.

How do I know if my expansion vessel is faulty?

The first signs are when your heating is on, the pressure will rise on the gauge on the front of your boiler.

When your boiler gets to 3 bar in pressure on the gauge this will activate the pressure relief valve. The water will be evacuated through the pressure relief valve that is preset to operate at 3 bar of pressure for safety reasons.

When the boiler cools down the pressure will go back down to zero bar pressure.

It’s at this point your boiler will go to fault mode for low pressure and you need to fill the system back up with water.

The outlet for the pressure relief valve is commonly on the outer wall of your boiler. You should be able to see water coming out if activated or a wet patch going down the wall from the outlet. If this is happening on a daily basis you really do need to get this fault rectified.

Adding fresh oxygenated water all the time will cause a lot of rust corrosion to the system which is not advisable for the long term health of your central heating system.

There are other causes for your boiler losing pressure with no sign of a leak.

This could include a cracked and corroded primary heat exchanger and ground floor leak that is not viewable without taking floorboards up or possibly the pipes have been laid in a screed of concrete without suitable protection causing pinholes due to corrosion.

If you suspect you have a leak it is best to get it investigated as soon as possible.

Call today on 01274 317169

A Guide To Low Water Pressure For Your Boiler

It’s almost inevitable that your boiler is going to have a problem sooner or later, the most common issue is having low water pressure. If this is the case for you, this guide should help you be on your way with a fixed, working boiler in no time.

This problem can be easily identified yourself and rectified with ease, in most cases by simply adding more water to your central heating system, commonly known as topping up. When there is a loss of pressure the boiler will go into fault mode to protect itself from any potential damage while running on low water.

To top up the boiler you simply need to add water through a filling loop. This is generally done by opening 1 or 2 valves to release water into the central heating system to fill up the radiators. This could be a manufacturer’s in-built filling loop that is connected to the boiler or an aftermarket filling that in most cases is fitted just below the boiler. Here is an image of an aftermarket filling loop.

As you can see from the picture the 2 black handles will need to be opened to allow water to be added to your central heating system. Do this slowly as the water gauge can go up very fast and you could end up having too much water in the system. Water will also naturally dissipate over time in the system and need a refill generally between 6 and 12 months but can be longer.

Afterwards, you should bleed the radiators, to release any air and allow the whole radiator to heat up.

Once this is done, the first thing to look at is the pressure gauge dial on your boiler, this will give an indication of how much pressure there is in your central heating system. If you don’t have a pressure gauge on your boiler then this may be displayed on a digital control panel on the front of the boiler. Ideally the pressure reading should be between 1 and 1.5 BAR, the unit that pressure is measured in.

Low water pressure can occur naturally over time or may be a result of a leak on your central system pipework and radiators or it could be an fault within the boiler. Please see our future posts for information on these issues.

Your digital control panel may display an error code if you don’t know what it means, see the list below of the most common errors and their meanings:

(F1) – Ideal
(E118) – New Baxi/ Main & potterton
(E119) – older Baxi/ Main Potterton
(F37) Ferroli
(ER04) – Biasi
(0.0) – Intergas
(F22) – Vaillant
(A281) or (EA338) – Worcester Bosch
(F22) – Glow Worm
(1P4) & (108) – Atag
(37) –  Johnson Starley
(10) – Alpha
(e302) Navien
(108) – Ariston
(21) – Saunier Duval
(E08) , (08E) , (F83) & (28) – Ravenheat
(Al02) – Sime
(AL40) , (AL41) & (A04) – Vokera

If your boiler is not showing any error codes it doesn’t mean it is fine as not all combi boilers will show an error code, some of them use a system of flashing lights to give you an error code. If you are unsure, it is always best to give us a call so we can help further.

Common causes/checks of low water pressure.
The boiler will naturally lose pressure over time due to the constant heating and cooling of the water. In this case you shouldn’t need to fill up the system more than every 6 -12 months, sometimes even longer.
You have a leak on your central heating system. The most common places to look are on your radiators, checking the valves at the bottom of the radiators and the bleed valves and caps at the top of the radiators. A common thing to look for is an orange/rust coloured stain around the valves.
If you have access, look at all the pipework, giving a good look around and under the boiler.
Check underneath the boiler itself.
Check your ceilings, you may see a damp patch indicating a leak from pipework or a valve where the water trickles down the pipe.

If you have exhausted these issues then it may be that your boiler is leaking internally. In most cases this will be a cause of a faulty expansion vessel. This is the vessel that works by taking up the expansion of water when it is heated. If it is faulty there is nowhere for the water to expand so the pressure will rise and when it reaches 3 bar on your dial the pressure valve will activate and evacuate the water outside your home. You will commonly see this pipe on the outside wall to where your boiler is installed.

*****Fun Pub Quiz Fact***** water expands in size by approximately 4% when heated up-to 100 degree’s centigrade.

If you have any questions or are still uncertain how to check or fix low water pressure, feel free to give us a call and we will be more than happy to help you get the issue sorted out.

Top 5 Common Vaillant Fault Codes

Is your Vaillant boiler showing a fault code and you have no idea what that code means? Having a faulty boiler always seems to happen at the worst times and when you need it the most. Generally this is in winter because it’s when your boiler is used the most. So from our experience at the Bradford Boiler Installation Company here are the top 5 error codes that come up on a Vaillant boiler display.

Vaillant were the first manufacturer to develop a combi boiler and have been at the forefront of combi boiler technology ever since. They have a great reputation for manufacturing and reliability. Vaillant is the only brand to have been awarded the Quiet Mark accreditation by the International Eco-Award Scheme to manufacturers of the quietest products. Vaillant has dedicated engineers for warranty repairs and have dedicated training centres across the uk for engineers to keep their knowledge up to date with their boiler advancements.

Fault 1: Code F22

When F22 shows on the boiler display this indicates the water pressure is low. You can check the pressure gauge dial on the front of your boiler if it has one, or newer models the digital display will show how much pressure is in the system. Once topped up to the desired pressure the error F22 error code will disappear. In some instances you may have to press reset on the boiler. Ideally the pressure will need to be between 1.0 and 1.5 bar. This is an easy fix that anybody can attempt however if you put too much pressure in the system don’t panic. Just bleed a radiator till the pressure drops to the required level.

Newer Vaillant Boilers have a built in filling loop under the boiler. These levers are grey and there will be two of them, one either side directly underneath the boiler. They will have closed written on them. Each valve (lever) should be in the quarter to 3 position (imagine it being a clock) open the right valve first to the 12.30 position then open the left valve till you have the desired pressure.  

Watch this video from vaillant to see how easy it is.


Fault 2:  F75

If you get F75 showing on the boiler display, this is probably going to be the pressure sensor that is blocked and cannot detect the pump spinning and the increase in pressure when the boiler goes to fire up. It may also be a faulty pump. This commonly happens on boilers and systems that have not been properly flushed to remove sludge or have not had a magnetic filter fitted. The easiest solution is to get a Gas Safe Engineer to replace the sensor.

Fault 3: Codes F27 & F28

These two codes commonly refer to a frozen condensate pipe. Generally this is the white drain pipe underneath your boiler that goes outside to a drain and it has frozen in the cold weather. This causes a build up of water that backs up to the boiler causing it to stop working/ lock out to error and f27/f28 will appear. This is generally an issue because the waste pipework is not a large enough diameter or the pipe is run horizontally or slightly uphill causing the waste pipe to freeze in very cold weather.

An easy fix is to run hot water from a kettle over the pipe to defrost the ice. This may take a long time and in extended bouts of freezing weather it will repeatedly freeze up. You could disconnect the pipe under the boiler if you feel confident enough and put a container there to catch the water. Beware when doing this initially there will be a lot of water. 

The ideal situation is to either upgrade the pipe to a larger diameter or consider running the pipe to an internal waste if possible or consider a trace heating kit that activates in freezing weather to stop the pipe freezing up.

Only attempt these fixes if you feel confident to do so, if you’re in doubt, always use a Gas safe Engineer.

Fault 4: Code F28 (Vaillant Turbomax)

This fault is very common for the Vaillant Turbomax, caused by a faulty ignition, or no gas getting to the boiler. The faulty ignition leads to no spark being generated. Alternatively there may be a gas valve issue or if you are on a meter check you have credit as you may have run out of gas.

In this instance you will need to get a Gas safe Engineer out to fix the issue.

Fault 5: Code F62

Before being able to fix the fault, a heating engineer will first need to find the cause, because there are several possible reasons why you’re seeing the F62 error, such as:

The gas valve is jammed stuck
There is an issue with the PCB (printed circuit Board) communicating with the gas valve.

In some instances both gas valve and PCB can be at fault. You will need the services of an Engineer to determine what the underlying cause of this fault is.


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