This page details most of the main components inside a Vaillant ecotec combi boiler, what they do, and some of the faults codes associated with each component.
Vaillant Ecotec Combi Boiler Individual Components And What They Do
1) Primary Heat Exchanger
2) Air Intake Tube
3) Pressure Sensor
4) Gas Valve
5) Plate Heat Exchanger
6) Automatic Bypass
7) Aqua Sensor
8) Thermal Fuse
9) Burner Door
10) Expansion Vessel
11) Spark Electrode
12) Fan
13) Automatic Air Vent
14) Printed Circuit Board
15) Diverter Valve
16) Pump
17) Pressure Relief Valve
Primary Heat Exchanger
The Primary Heat exchanger is responsible for producing all the heat the boiler needs for producing hot water and heating.
Early ecotec models use heat exchangers manufactured by a company called Giannoni. Later models use heat exchangers manufactured by Sermeta.
Fault Codes associated with the Primary Heat Exchanger include the F.76 fault code.
Not such a common fault code but the F.76 is the only fault code you may see directly related to the main heat exchanger.
There is a non replaceable Thermal Fuse(see number 8) at the top of the heat exchanger. If this fuse pops it means your heat exchanger is beyond repair and needs to be replaced.
Typically the F.76 fault will be permanent and the boiler won’t work, but I have seen some Vaillant boilers that will work intermittently and can be reset.
The F.76 fault code is usually caused by the heat exchanger overheating, which could be caused by blockages or air in the heat exchanger.
Other problems with the main heat exchanger that may not present a fault including a loud noise when running. The noise could be described as a loud humming or vibrating noise.
It doesn’t sound good but it is usually ok to keep using the boiler if you experience this.
This noise is caused by kettling(water boiling) inside one of the coils inside the heat exchanger. Solving this problem usually requires replacing the heat exchanger as its difficult to flush out.
The Primary Heat Exchanger serviceable component, but only the burner side can really be serviced typically.
This component typically retails for around £500.
Air Intake Tube
Not much to say about this part really. It’s not actually an air filter but does have a sponge inside of it to reduce noise. The boiler won’t run properly with this part removed as it affects the air/gas ratio.
It doesn’t usually fail unless the burner door seal fails which causes it to melt(see number 9).
The Air Intake Tube in a non serviceable component.
This component typically retails for around £40.
Pressure Sensor
The pressure sensor is a common failure point on Vaillant boilers that use this in their design.
Common fault codes related to the Pressure Sensor include the F.75 fault(very common), the F.22(means low system pressure) and rarely you may see an F.73 fault(printed circuit board not communicating with sensor).
The pressure sensor is prone to getting blocked or not reading properly.
The pressure sensor does two jobs. It is there so the boiler knows how much pressure is in the it, and when the pump runs it detects a small rise in pressure.
The boiler will not run if the sensor or the pump is faulty and will come up with the F.75 fault code.
The Pressure Sensor is a non serviceable component, but it can be tested to see if it’s working accurately.
This component typically retails for around £25
Gas Valve
The Gas Valve is responsible for delivering the correct amount of gas to the burner, and stopping the flow of gas to the burner when there is no demand.
Modern Vaillant boilers modulate, which means the burner output or speed varies depending on the load to increase efficiency. For the boiler to modulate the fan speed is variable and the gas valve has to reduce the flow of gas to match the speed of the fan.
Common Fault codes associated with the Gas Valve include the F.28(burner fails to light) and F.29(burner goes out during operation).
On later models from 2012 onwards you may see and F.54 fault code in conjunction with F.28 or F.29 fault code.
On Vaillant ecotec Combi boiler manufactured from 2005 – 2012 is very reliable and rarely fails. On Vaillant ecotec Combi boiler models manufactured from 2012 onwards, gas valve failure is not uncommon.
The Gas Valve is a non serviceable component, but the air/gas ratio can be adjusted on this part.
This component typically retails for around £150 – £200 depending on model.
Plate Heat Exchanger
The Plate Heat Exchanger is responsible for producing the hot water that comes out of the taps.
Vaillant ecotec Combi boilers are what you call an “indirect design”. This means that there are two heat exchangers. The primary heat exchanger indirectly heats up the clean drinking water coming out of the taps via a secondary heat exchanger which is the plate heat exchanger.
Common faults with the plate heat exchanger include, blockages which cause the hot water temperature to fluctuate or not work at all. Its not uncommon for the plate heat exchanger at the back to leak but this is not a direct fault of this part.
In general Vaillant plate heat exchangers do not fail and are quite reliable.
The Plate heat exchanger is a not officially a serviceable component, but these can be flushed out with acid to restore them if they are blocked.
This component typically retails for around £100 – £200 depending on model.
Automatic Bypass
The Automatic Bypass is actually part of Diverter Valve(see 15). It is a simple valve which is spring operated and designed to open once the pressure get high enough to overcome the force of the spring.
This part doesn’t usually fail or cause problems.
The bypass is there to allow the water to flow directly from the flow pipe back to the return inside the boiler if the central heating flow is shut off(due to a closed zone valve for example). This is designed to protect the pump and prevent the boiler from overheating.
The Automatic Bypass is a non serviceable component, but the tension on the spring can be adjusted.
This component typically retails for around £22.
Aqua Sensor
The Aqua Sensor, as Vaillant likes to refer to it as, is essentially a flow switch or sensor which is designed to detect when a hot tap is flowing.
On Vaillant ecotec Combi boilers this part is quite reliable and doesn’t tent to fail, although they can leak but it is rare in my experience. If this part fails to detect a tap running you would have no hot water as a result.
The Aqua Sensor is a non serviceable component, but it can be tested.
This component typically retails for around £25.
Thermal Fuse
The Thermal Fuse is something built into the design of Giannoni and Sermeta heat exchangers.
Typically the Thermal Fuse doesn’t fail unless provoked.
If the Primary Heat Exchanger(see 1) gets over heated beyond a certain point, it can trip the Thermal Fuse and should display the F.76 fault code.
Typically the F.76 fault will be permanent and the boiler won’t work, but I have seen some Vaillant boilers that can be reset and will work intermittently.
The F.76 fault code is usually caused by the heat exchanger overheating, which could be caused by blockages or air in the heat exchanger.
Seeing the F.76 fault code means you need a new Heat Exchanger, the Thermal Fuse itself cannot be replaced.
The Thermal Fuse is a non serviceable component, but it can be tested.
Burner Door
The Burner door connects to the Primary Heat Exchanger. The Burner Door is connected to the Venturi which carries the Air/Gas mixture through to the Burner to be burnt. The Air/Gas mixture is blown through to the burner via the Fan.
The Burner Door on Vaillant ecotec boilers doesn’t usually cause problems or fail, HOWEVER the gasket(G10) which creates the seal between the Primary Heat Exchanger and Burner Door can and does fail.
On Vaillant ecoMAX boilers and early ecotec models, the burner gasket was made of a material which was prone to failure over time.
These gaskets were later upgraded to a seal which was made of graphite and more durable. These are less prone to failure.
Vaillant recommends that the G10 graphite burner door seal is replaced every five years at minimum.
One cannot open the burner door(to clean the heat exchanger for example), without replacing the gasket. This is because the seal is damaged once the door is opened.
If the burner door on your boiler has been opened without the seal being replaced, then you’re at serious risk of it failing and causing serious damage to your boiler.
On some ecotec models there is also a little rubber seal below the main graphite gasket which also fails and needs to be replaced periodically. In my experience these rubber seals only last between 3 – 5 years before they start to fail and leak.
The Burner Door is a non serviceable component, but the sealing gasket can and does need to be replaced every five years minimum, as per Vaillant’s recommendations.
This component typically retails for around £150. The G10 burner door seal typically retails for around £25.
Expansion Vessel
The Expansion Vessel is essentially a container with a rubber diaphragm inside of it. The diaphragm is designed to be set to a pressure typically somewhere between 0.75 and 1 bar.
Typical problems with the Expansion Vessel include, flat diaphragm(no pressure), failed diaphragm(won’t hold pressure) or leaking when the seam on the vessel fails.
When you put the central heating on, the water in the system expands when it is heated up. this means you generally have an extra volume of water which needs to go somewhere.
Water expands by 4% when it is heated(below 100 degrees centigrade). If your central heating system holds 100 litres of water, then your boiler needs to make room for an extra 4 litres of water when it is warmed up. This is the job of an Expansion Vessel.
The expansion accommodates this extra volume until the heating is turned off and the system cools down again. The diaphragm then goes back to its original position.
The diaphragm inside of an expansion vessel goes flat over time which is normal, just like a car tyre does. If the pressure inside the diaphragm of the vessel is not recharged periodically(on a service for example), it will lose all of its pressure – its inevitable.
The Expansion Vessel is a serviceable component, the internal diaphragm needs to be re-pressurised periodically. During a boiler service is an excellent time to service the expansion vessel.
This component typically retails for around £130.
Spark Electrode
The Spark Electrode on a Vaillant ecotec boiler is responsible for lighting the burner and detecting if the burn is lit.
The Spark Electrode itself doesn’t usually fail or cause any problems directly. The lead which connects the electrode to the printed circuit board can fail occasionally though.
The Spark Electrode actually does two jobs. First it sends a high voltage current which create a spark which lights the burner.
Secondly, once the burner is lit, it sends a low voltage AC current through the electrode which is used as part of the Flame Rectification process so the boiler can know if the burner is lit or not.
The flame from the burner will actually conduct electricity. It also converts the AC current from the electrode to a small DC current which then flows back to the printed circuit board via the boiler chassis. This is how the boiler knows the burner is alight.
The Spark Electrode is a serviceable component which can be cleaned. The gasket between the electrode and burner door can be replaced.
This component typically retails for around £25.
Fan
The Fan on a Vaillant boiler is responsible for blowing the Air/Gas mixture through the Venturi and through the burner where it can be burnt to create heat.
On most Vaillant ecotec models manufactured from 2005 – 2012 the fan is a very reliable component and rarely fails.
On 2012 models onwards the fan can and does fail.
The Fan is a non serviceable component.
This component typically retails for around £150 – £200 depending on model.
Automatic Air Vent
The Automatic Air Vent is a de aerator which is designed to remove any air from the boiler/system.
The auto air vent is a bit of a delicate part and prone to failure which means either not venting or leaking. It could be regarded as a service item.
The auto air vent works using a little float which drops when there is any air below it, and vents the air out around a little pin which drops down off of its seat.
The Auto Air Vent is a non serviceable component. Some of the older ones could be cleaned, but the newer plastic ones are not worth wasting any time on.
This component typically retails for around £20.
Printed Circuit Board
The printed circuit board(pcb), is the main control unit or brain on a Vaillant boiler(or any boiler).
The PCB on Vaillant ecotec boilers is a very common failure point. Expect there is a good chance you will need to replace this part on your boiler at some point if you have one of these models.
PCB failure is common on the older models manufactured between 2005 – 2012, as well as models manufactured from 2012 onwards.
Common fault codes associated with PCB failure include the F.27, F.61, F.62, F.63 and even the F.64 fault code.
On newer models its not uncommon for the display to just go blank and then come back on later until a demand is put on the boiler again at which point it goes off again.
I have also seen PCB failure cause other intermittent fault codes which include the F.75, F.28 and even the F.23 fault code. This happens typically on older models(pre 2012).
The printed circuit board is a non serviceable component, although various settings and parameters can be adjusted.
This component typically retails for around £200 – £230 depending on model.
Diverter Valve
The Diverter Valve on a Vaillant boiler – which uses an indirect design, is responsible for switching between Hot Water and Heating.
The Diverter valve is a very common failure point on Vaillant Combi boilers. They are prone to leaking mostly, they can stick and the motor that operates the valve can fail.
The Diverter Valve on ecotec boilers uses a piston with a “pin” that operates back and forth via an electrical motor. The pin seal can wear out and fail which results in a leak.
This is a poor design in my opinion. The “paddle” design diverter valve on Worcester boilers and later Ideal Logic’s is a much better design in my opinion, which is much less prone to failure.
The Diverter Valve is a non serviceable component. The bypass on the valve can be adjusted. Applying a little Silicone Grease to the pin can help keep it moving freely and help prevent the pin from seizing.
This component typically retails for around £90 for the plastic version, or around £140 for the brass version.
Pump
The Pump on Vaillant ecotec boilers is responsible for distributing the heat away from Primary Heat Exchanger down the flow pipe for heating, or through the Plate heat exchanger for hot water.
Early models manufactured from 2005 to around 2010/2011 had WILO pumps which were extremely prone to failure. A lot of them have been replaced, but I still come across a lot of WILO pumps which are still working ok.
Later Grundfos models are a lot more reliable and tend not to fail as much. In my experience, the average life expectancy for a Grundfos pump is somewhere between 10 – 15 years.
I have seen some Grundfos pumps exceed the 20 year mark before needing replacement.
The Pump is a non serviceable component. However the pump strength can be tested and the speed of the pump can be altered on most ecotec Plus models.
This component typically retails for around £165.
Pressure Relief Valve
The Pressure Relief Valve on a Vaillant ecotec Combi boiler is designed to relieve some pressure should the boiler/system become over pressurised.
Pressure relief valve’s don’t typically fail unless provoked.
A dripping pressure relief valve is usually just a symptom of other problems which usually relate to issues with the expansion vessel, or filling loop valves(failure or left open by mistake).
Over pressurisation can also be called by a failed plate heat exchanger leaking internally, but this is very uncommon on Vaillant boilers in my experience.
If a pressure relief valve is dripping it will cause a boiler to lose pressure.
The Pressure Relief Valve is a non serviceable component. Sometimes they can be cleaned and replaced, but most of the time it’s worthwhile just replacing them.
This component typically retails for around £20.