Vaillant ecotec plus 637 problems: Top 10 Most Common Boiler Problems

Top 10 Most Common Boiler Problems

Boiler problems can cause a significant headache, particularly during the winter months. From leaks to cold radiators, boilers can suffer from a wide range of issues if not serviced regularly. Fortunately, most of the most common issues are easy to identify and can easily be fixed by a Gas Safe registered engineer.

Below we have listed the top ten most common boiler problems across all types of condensing boilers.

Summary of topics:


Hot water but no heating

Low boiler pressure

Boiler kettling

Frozen condensate pipe

Boiler not responding to thermostat

No heat or hot water

Boiler keeps switching off

Strange boiler noises

Pilot light going off

Boiler leaks

One of the most common boiler issues is a boiler leak. Leaks can be a nuisance because not only can they cause water damage to a home, but water can also cause electrical components in and around the boiler to malfunction.

A leaking boiler can be due to a number of things:

  • Excessive boiler pressure
  • Corroded pipes or tanks
  • A faulty Component
  • Leaks from seals

A leak should always be treated as a serious issue. If you find a leak you should call a qualified heating engineer as soon as possible to investigate. Do not attempt to remove the boiler casing yourself to find the source of the leak.

Hot water but no heating

A common boiler issue people face is when a home has hot water but no central heating. This can happen because of several reasons.

Firstly, if you have a combi boiler, it might accidentally be set to only heat water but not the central heating. This can happen if the boiler is set to this mode during the summer months when radiators do not need to be heated but is forgotten about. It may also be that the boiler is set to turn on at an unexpected time. Check the boiler display to see if this is the case.

Another cause could be that the boiler is working fine but there is trapped air in the radiators stopping them from heating up. The solution there is to bleed the radiators to allow the trapped air to leave the system.

If your central heating system is still not turning on, despite having hot water, it may be that the boiler or heating system is faulty. A Gas Safe registered engineer will be able to investigate the fault and find the source of the issue.

Low boiler pressure

Low boiler pressure can lead to cold radiators and a lack of hot water. Low boiler pressure can be identified on the boiler display panel, where either a digital or physical dial will show the level of pressure in the system. The most typical pressure level should be around 1.5 bars, with slight variance depending on the boiler manufacturer and model.

A boiler’s pressure can drop due to two main reasons:

  • A leak in the system will result in not enough water being present in the system, consequently causing the pressure to drop.
  • A bleeding radiator can also reduce system pressure.

Low boiler pressure can be fixed by repressurising the boiler. This involves opening the boiler filling loop to allow water to re-enter the system. Check out our guide on repressurising a boiler to see the full list of steps to follow.

Boiler kettling

Another common boiler problem is kettling. Boiler kettling occurs when water is heated too quickly and reaches boiling point, causing steam to be generated and air to become trapped. The trapped air gives off a whistling sound, like a kettle.

Boiler kettling can be caused by limescale build-up, which slows down the flow of water in the system and causes it to heat up excessively. A faulty component on the appliance could cause the boiler to heat up water to higher temperatures than expected.

A boiler engineer will be able to inspect the system and identify the cause of the kettling. There is a solution to this problem which depends on the severity. Sometimes the noisy component can simply be cleaned using different methods, alternatively replacing the parts may be required.

Frozen condensate pipe

A frozen condensate pipe is an issue that many people face during the colder months. Every condensing boiler has a pipe that transports waste water produced during the condensing process outside the property. If temperatures drop below freezing, the water in the condensate pipe can become frozen, forcing the system to shut down automatically as a precautionary measure.

The best way to fix a frozen condensate pipe is to pour warm water onto it to thaw it. This should allow waste water to exit the pipe, meaning the boiler can turn back on. For further detail on this, check out our guide on how to safely resolve a frozen condensate pipe.

Boiler not responding to thermostat

There are a wide range of thermostats that homeowners can choose from to help increase the efficiency of their homes. These thermostats can work great, but it can also be frustrating when the boiler stops responding to the thermostat.

If you suspect that your boiler is no longer working with the thermostat, first make sure that the temperature on the thermostat is above the current room temperature. If it is not, then the thermostat is likely working fine.

If the room temperature is below the thermostat temperature, try replacing the batteries in the thermostat or moving it closer to its receiver. If this does not work, it may be that the thermostat is faulty and needs to be replaced.

No heat or hot water

If your boiler has left you without heat or hot water, there is definitely something wrong with the system. A boiler may stop providing central heating or hot water for several reasons:

  • The boiler has become disconnected from the power, gas or water supply. These connections can be switched off accidentally or during a power outage.
  • If the boiler pressure becomes too high or too low the system turns off automatically, causing a lack of heat and hot water
  • Piping issues, such as frozen condensate pipes or airlock, can stop a boiler from functioning.
  • Along with various safety features built into the appliances that would display other faults.

A lack of central heating and hot water can be down to any number of these things, so it’s always best to call a Gas Safe registered engineer to inspect the boiler and resolve the issue.

Boiler keeps switching off

If left unserviced, a boiler may over time begin to randomly switch off. There are a number of potential reasons for this, including:

  • Trapped air in the system
  • Low boiler pressure
  • High boiler pressure
  • A faulty thermostat
  • Debris and sludge building up in the pipes

If you notice that your boiler keeps switching on and off, it may be because of one of these faults. Depending on the severity, a qualified engineer will be able to say whether the problem can be fixed, or whether a new boiler is needed.

Strange boiler noises

Beyond boiler kettling, there are a wide range of strange noises that a boiler can make:

  • Gurgling noises – this is a sign of trapped air in the system.
  • Drone noises – this is usually caused by a faulty pump.
  • Humming noises – this usually happens if water arrives from the mains at too high a pressure
  • Whooshing noises – this occurs when debris blocks the air intake pipe or if air filters in the system become blocked by dust.

Strange boiler noises do not usually mean there is an immediate danger with the system. Nonetheless, an engineer should be called as soon as possible to investigate.

Pilot light going off

If you have an older boiler you may have a pilot light that needs to be constantly lit to light the larger boiler burner. However, over time the necessary parts for lighting the pilot switch can become faulty, such as the thermocouple.

If your pilot light keeps turning off, do not try to repair/replace this yourself. This would require taking off the boiler casing, which is illegal unless you are registered with the Gas Safe Register. Instead, first check that your other gas appliances are working correctly. If they are not, the issue might be with the gas supply itself.

If the other gas appliances are working correctly, there may be a faulty part, so call a Gas Safe registered engineer to resolve the problem. Newer boiler models are not built with pilot lights so do not suffer from this issue.


  • Boilers can suffer from many problems, most of which should be resolved by a qualified boiler engineer.
  • Boiler leaks should be treated as a serious issue and resolved as soon as possible.
  • A lack of central heating could mean that the radiators need bleeding.
  • Low boiler pressure can be caused by leaks and can be solved by opening the filling loop.
  • Boiler kettling can make a lot of noise and sometimes requires the system to be cleansed or for a part to be replaced.
  • Frozen condensate pipes can be thawed using warm water.
  • A boiler may not respond to a thermostat if the thermostat runs out of battery or is placed too far away.
  • A lack of hot water and central heating is usually a larger issue that definitely needs the help of a boiler engineer.
  • If a boiler keeps switching off, an engineer will be able to say whether a part needs replacing or if the entire boiler needs to be replaced. Sometimes this is more cost effective.
  • Boilers can make lots of strange and distracting noises, such as gurgling and humming.
  • Never attempt to replace any parts yourself. An engineer is best to fix any issues safely.

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Common Vaillant boiler problems & fixes

At Homecure we’ve been providing installation, repairs and boiler servicing for Vaillant boilers for a number years, with our Gas Safe engineers able to deal with any issue you are experiencing. This has enabled us to build up years of knowledge and experience to provide solutions to all kinds of Vaillant boiler problems.

In many cases a Vaillant boiler with water pressure problems is a common reason for a breakdown, faulty pumps and gas valves or frozen condensate pipes. Even in situations where an error code is displayed that is not so common we understand how to apply a suitable fix.

There are some instances where you may be able to resolve the problem without calling an engineer, which we explain in more detail below. However, for those that require part changes, internal boiler checks or anything requiring technical expertise, you should always get in touch with a qualified engineer.

Read through our list of common breakdowns and fixes below to learn more about what to do when Vaillant boilers need troubleshooting and what to do next time you experience a fault.

Top 10 Vaillant Boiler Problems

1. Low water pressure

When you see a Vaillant boiler F22 error code this means water pressure is low in the system. A Vaillant boiler with low water pressure can usually be fixed by opening the external filling loop to raise the pressure back to 1.5. Often seen on an ecoTEC plus 428 with problems. If you own a this sort of model, use the built-in filling loop instead, as detailed in the manual.

2. Faulty pressure sensor or pump

Vaillant ecoTEC boilers are known for displaying the F75 code which means the system cannot find the right amount of pressure while the pump is working. This would require one of our team to visit to check whether it is the pump or pressure sensor that needs to be fixed.

3. Failed ignition

Vaillant boiler problems with no hot water or heating is quite common, which will produce a Vaillant F29 error warning. It can be the result of a frozen condensate pipe, lack of gas supply or defective spark electrodes. This is a common issue Homecure engineers are able to diagnose and resolve. A Vaillant F28 error code also related to the same issue.  

4. Incorrect flame detection

If the gas supply and ignition aren’t deemed as being safe the boiler may show up a Vaillant f27 error warning, which will lead to a lockout. You will need to contact a professional Gas Safe engineer who can provide boiler repairs to fix this issue, which could be associated with moisture in the electrical parts, worn down ignition leads or a faulty printed circuit board.

5. Frozen condensate pipe

A frozen condensate pipe can create a number of problems on different Vaillant boilers. If this is the cause you can usually fix this yourself by thawing it out with warm water. However, if you do not feel confident taking this sort of action, the Homecure team are always available to help.

6. Slow flow rate

Sometimes you may experience a slow rate of water coming out of taps and shower heads in the home. This problem may be related to the pump, the height position of your water tanks or be linked with an open-vent heating system.

7. Faulty gas valve

If the gas valve has become stuck it could create a dangerous situation that leaves the supply running instead of being closed off after the hot water or heating has been turned off. This displays the F62 and will require a Gas Safe engineer to attend – a task the Homecure will be able to assist with.

8. Over activity

A Vaillant ecoTEC Plus 832 with problems related to over activity could be caused by a faulty thermostat or temperature settings. If you find it is firing up unexpectedly during the day, check the temperature levels against the time period to avoid it becoming active when you don’t want it to. The Vaillant ecoTEC Plus 831 had problems similar to this, but this model has now been discontinued.

9. Sensor faults

If you experience either a F52 or F53 fault code this indicates an issue with the mass flow sensor. On Vaillant ecoTEC boilers these are located just behind the gas valve and are connected to the fan. This will require an engineer to conduct an electrical test to verity the issue and install a replacement if needed.

10. Unstable flame

A Vaillant boiler producing the F68 error code means the flame is unstable which could be caused by a number of reasons. This includes the gas flow pressure being too low, a frozen condensate pipe or air being present in gas. One of our qualified team members can resolve this quickly and safely.

Which Vaillant boiler problems need a Homecure engineer?

Vaillant boiler repairs can be the result of a number of different issues. The table below describes the most common reasons for a breakdown and whether or not you will need to call out a Homecure engineer.

Boiler issue

Possible reason

Should I call a Homecure engineer?

Banging noises or whistling

This is usually caused by air in the system or by low water pressure leading to kettling.


Frozen condensate pipe

This will produce an error code on the boiler warning you of the problem.

Maybe – you can try to defrost the pipe using warm water but if that doesn’t work you should give us a call.

No heating or hot water

There can be a number of reasons for this, either to do with valves, water levels or thermostat issues.



Leaks are typically the result of a broken piece of equipment and may not always be externally visible


Low pressure

May be caused by a leak, faulty valves or radiators that need to be bled.

Can usually be fixed at home by using the filling loop, but if not, give us a call.

Problems with thermostat

This may be related to current timings and settings.

Yes – it may need to be replaced if this does not resolve the issue

Boiler shutting down

May be the result of a faulty thermostat, low water pressure, low water flow or faulty air pump


No pilot light

A broken thermocouple could be the cause for this.


Cold radiators

Radiators not heating up when turned on could be caused by a build-up of air or sludge in the system.

You can bleed the radiators with a key – if this doesn’t fix the issue, or you aren’t comfortable doing it, call our team.

Kettling noises

Caused by a build-up of sludge or air in the heat exchanger.


Our team at Homecure offers a range of services across a number of other brands, including boiler repairs for Worcester, Glow Worm and Baxi.

Vaillant boiler error codes

There are a long list of Vaillant error codes and below we explain some of the most common to help you understand what they mean and how they can be fixed.

Error Code



This relates to a lack of water or pressure and can be fixed by opening the filling loop to return the pressure level back to 1. 5.


Can be caused by a faulty gas valve or printed circuit board (PCB), or a defective flame sensor. An engineer can diagnose the issue, although if related to the PCB, a new boiler installation may be cheaper.

F28 & F29

Caused by a boiler lockout which stops access to heating and/or hot water. Can be linked to the gas valve settings, the condition of the ignition unit or ignition leads, or the air inlet duct.


A Vaillant ecoTEC Pro 28 with problems usually displays this code, caused by a faulty heating pump or pressure sensor or sometimes both. This can be fixed with part replacements.


May be a result of a jammed gas valve or faulty communication between the PCB and gas valve. An engineer will check to diagnose the fault.


This will display when the boiler overheats due to low water pressure. Opening the filling loop so the pressure level can go back to 1.5 should fix this.


Issues with the fan or flue tend to be the cause of this error code displaying. The flue can be unblocked by an engineer, or they can replace the fan, if needed.


A faulty gas valve is likely to produce this Vaillant error code. This will be different to an incorrectly adjusted valve and can be replaced by an engineer.


The F63 error code will be linked to the PCB, which will require an engineer to use a multi-meter to determine the exact cause of the issue.


If the flame is either constantly weak or keeps going out it will produce this code. An engineer can diagnose if it is down to a blocked flue, faulty fan or air pressure switch or an incorrectly adjusted gas valve.


FAQs about Vaillant boiler problems

What is wrong with my Vaillant boiler?

The best way to find out what is wrong with your Vaillant boiler is to cross check the error code with the user manual. Sometimes you can resolve the issue yourself, however, if you see an F60 error on a Vaillant Turbomax Plus 824/828E system this means a gas valve control is defective and requires a qualified engineer to fix it.

How do I reset my Vaillant boiler?

There are a number of reasons you may want to reset your Vaillant boiler, if it is locked out for example, and it’s an easy process to complete. Press and hold the reset button for a couple of seconds which should get things back to normal. If not, one of our engineers will be able to help.

Why is my Vaillant boiler losing pressure?

Low pressure can be caused by a leak, or if a Vaillant boiler service is pending, it may just require a reset. If the F22 boiler error code is showing this means there is a leak in the system. Our Vaillant engineers can quickly identify and fix this issue to have the boiler up and running and again in no time.

How long should a Vaillant boiler last?

A standard Vaillant warranty lasts between 2-5 years. This can be extended up to 10 years in some cases. If the boiler is serviced regularly and kept in good condition it could last for at least 15 years.

Why does my Vaillant boiler keep turning off?

There can be a number of reasons why your Vaillant boiler keeps turning off. It could be due to low water pressure, a faulty thermostat, a faulty water pump, air in the system or frozen condensate pipes. One of our engineers will be able to find the issue and quickly apply a solution for you.

How do I turn on the heating on my Vaillant boiler?

How you turn the heating on with a Vaillant boiler may differ slightly depending on the model.