Vaillant, Glow-worm and Saunier Duval Boilers: Frequency Asked Questions

The section below covers our customer’s most frequently asked questions, based on over 40,000 service calls.

  1. What's the best advice on which type of gas boiler repair company to use?
  2. F.75 fault on Vaillant ecoTEC boiler
  3. Why does the boiler pressure keep dropping?
  4. Vaillant ecoTEC boiler sometimes fires up, when the heating is off?
  5. Do Glowcare provide a Vaillant ecoTEC annual qualifying service?
  6. What are your qualifications?
  7. What does a boiler service comprise of? H how often should my boiler be serviced?
  8. Do you carry replacement parts?
  9. What is "fair pricing"?
  10. What if I smell gas?
  11. Where will you travel to?
  12. Boiler displays an "F" code fault

Which, out of the different types of gas boiler repair companies that are out there, should I be looking at - to achieve a prompt and correctly priced repair for my faulty/broken combi boiler?

Best Advice –

First, check out your boiler manufacturer’s own service team. They will offer expert service and repair for all of their own boiler’s makes and models.

You might also consider using the manufacturer’s approved boiler/furnace service agent for your area.

Alternatively you could try to locate an independent repair specialist for your boiler type. Hopefully it shouldn’t be too difficult to find one that covers your area.

Another good reason to consider the three mentioned above first, is that the manufacturer, the agent and the specialist will all have real expert knowledge and know-how of your exact boiler model. Of equal importance is that they should all carry full van stocks with the required parts to achieve a quality, first time repair.


All parts don’t fit all boilers!


There’s something else that is important about the parts inside your boiler, that when fully understood could be of real help to you – when trying to select the best boiler repair company to use.

And it is this:

These days almost all modern gas boilers contain unique parts inside! This means that your boiler’s parts will almost certainly only fit your specific model.


If you’ve developed a major fault on your gas boiler, e.g. a F13, “blown printed circuit board” (PCB), or a burned out fan, or a stuck or jammed pump showing F75, (i.e. not a small fault e.g. pressure dropping), then unique parts will be needed. These parts will only fit on your particular make and model of boiler!

Really, AND THIS IS THE KEY, pretty much only the manufacturer, the agent, and the dedicated specialist would carry these unique parts with them as van stock, enabling a quick repair to be completed.


Here is a good example:

Our company carry between 30-40 different printed circuit boards (PCBs), believe it or not. This is just to cover the boilers that we specialise in, which in our case is Vaillant, Glow-worm and Saunier Duval. It’s that specific!

And also, it’s not just the condensing boilers from the last 7 or 8 years or so, which have unique parts in them. Going back to the “fan flued” combies of the eighties, they also pretty much were all made with unique parts as well.

To be fair, some of the much older cast iron boilers (not that many left now), did use some parts that were interchangeable with other boilers, e.g. universal thermocouples and some older gas valves etc.


Large national service companies – what’s to consider?

If you are thinking of using one of the large national boiler repair companies to carry out your boiler repair, then be sure to ask a couple of questions first, before deciding on which, if any, you should use.

Firstly, try to get assurances that their engineer will have good working knowledge and understanding of your particular make and model of boiler.

Secondly, get them to confirm that the service engineer who attends, carries the specific parts for your exact combi or system boiler. This should ensure that they will be able to get you up and running again, in just one visit.

Note –

If you are thinking of going for one of the large nationals, that’s fine but remember that they may not specialise in your make of boiler!

If you stop and think about it for a moment, the national companies have to attend and repair every conceivable make and model of wall hung or floor standing gas boiler that exists. Starting from A for Alpha boilers, right through to V for Vokera boilers, including all others in-between.

These big national firms could easily attend breakdowns for 60 or 70 different manufacturer’s boilers, most having unique parts?

So, find out who’s attending and what parts they are bringing!


Your local Gas Safe Registered service engineer/installer

Where you live, it might well be that there is indeed a very good, Gas Safe Registered, service engineer that you could use.

Nowadays there are many service engineers and gas installers who have attended and completed one of the very useful “Factory Training Courses” put on by leading boiler companies. These are provided for engineers and installers who want to gain more specific knowledge of the boilers that they work on, or fit.

It could also be the case that the installer who fitted your boiler (if it was installed not so long ago), is one of the growing group of independent installers who are loyal to only one manufacturer. For example, if they fitted Vaillant boilers, they would be called “Vaillant Advanced Installers”, i.e. installers who only install one manufacturer’s boiler, no others. This type of advanced installer may well be quite conversant (for repairs) with the brand that they install. This is definitely worth looking into.

F.75 fault on Vaillant ecoTEC pro and plus combi boilers

Our Vaillant ecoTEC boiler has stopped working and is flashing up an F.75 fault code on the small display screen. Do you know what causes this fault code and what needs to be done to fix the problem?

The F.75 fault code on a Vaillant ecoTEC boiler is usually caused by either:

(1) – Low Water Pressure

Low system water pressure, where the needle points down to zero (no pressure) on the boiler’s gauge or display, may be the cause of an F.75 fault code being displayed on the boiler.

ecoTEC plus: The boiler can be repressurised by opening the two “filling taps”, which are situated on the underneath of the boiler. This will then allow the boiler to start repressurising back up to 1.0 bar, following this procedure the taps will need to be closed again. If water starts leaking out from the boiler during repressurisation, stop refilling immediately and have the cause of the leak investigated. Once the boiler has been repressurised back up to 1.0 bar, press the reset button on the boiler (top left of the four buttons below the display) to restart the boiler.

ecoTEC pro: The boiler can be repressurised by locating the filling loop (not part of the boiler), which is usually a flexible silver pipe. This will need to be connected (if it is not already connected) to the system pipework for repressurising to take place. Once the flexible filling loop has been attached to the system pipework, the valve on the filling loop will need to be opened, this will cause the boiler to begin repressurising. Once 1.0 bar pressure has been reached, the tap on the filling loop needs to be closed and the flexible filling loop disconnected (if required by local/national water regulations). Once this has been done, the reset button on the boiler (top left of the four buttons below the display) needs to be pressed to restart the boiler.

(2) – Faulty Pump

The F.75 fault can also be caused if the boiler’s integral pump has failed or becomes seized (possibly due to dirty system water). This results in water not circulating from the boiler to the radiators. The boiler pump may need replacing, if this is the case, the system water should be cleaned and treated before a replacement pump is fitted. This work should only be carried out by a Gas Safe registered engineer or installer.

(3) – Faulty Pressure Sensor

The boiler’s “low water pressure sensor” becoming faulty can bring up an F.75 fault code. This is a result of the sensor not reading the water pressure correctly (possibly due to dirty system water). Replacing the low water system pressure sensor should only be carried out by a Gas Safe registered engineer or installer.

Why does the pressure keep dropping down from 1.0 bar to zero every day, on our combi boiler’s pressure gauge, causing it not to work again until we repressurise it?

We have checked thoroughly for leaks on the heating pipework (as we were told to do), but cannot find any leaks anywhere. What else could be causing this daily pressure loss?

A few customers unfortunately experience this annoying problem, where the boiler’s pressure gauge drops down to zero every day. This unexplained loss of pressure can sometimes be caused by a leak on the heating system’s pipework or radiator valve connections. However, we almost always find that the route cause of these pressure dropping problems is a fault within the boiler’s integral expansion vessel.

Due to lower than average winter temperatures in recent years, many gas boiler expansion vessels (which are inside or mounted on the back of the boiler) have become significantly deflated. We usually find that if pressure fluctuations occur on a daily basis, a deflated boiler expansion vessel diaphragm is the main cause.

Note – this problem can (rarely) be caused by a blocked vessel connecting tube. To achieve a good and lasting repair to the vessel a precise procedure is required. This needs to be carried out by someone who is experienced in successfully pumping up expansion vessels, therefore avoiding the unnecessary expense of replacing parts. This work should only be carried out by a gas safe registered engineer or installer.

Why does our Vaillant ecoTEC boiler sometimes fires up, even though the heating is switched off?

The most likely reason for a Vaillant ecoTEC Pro or Plus boiler to occasionally fire up when the heating is switched off, is that the boiler’s built-in hot water pre-heat facility (“Warmstart”) is activated.

When the warmstart system is selected, it is possible that you will hear your Vaillant boiler firing up for a few seconds once or twice each hour.

The boiler does this to maintain a stored amount of preheated water, so that when a tap is opened, hot water is immediately available.

Vaillant ecoTEC Plus – Warmstart

Activation of the warmstart system for the ecoTEC Plus, is achieved by turning the top hot water control knob, in the clockwise direction, until it stops turning.

The “C” symbol should now appear (flashing at first), then staying permanently on the display unit. This indicates that warmstart is now switched on/activated.

To switch off warmstart, turn the hot water control knob back in the anti-clockwise direction, all the way around until it stops turning.

Warmstart should now deactivate/switch off, and after a short time the “C” symbol will disappear from the display.

To set the desired hot water temperature, the hot water control knob will need to be turned in the clockwise direction, but keeping short of turning all the way around to the end (as this would switch warmstart back on).

Vaillant ecoTEC Pro – Warmstart

To switch the ecoTEC Pro warmstart system on, turn the top hot water control knob fully in the clockwise direction, all the way around until it stops turning.

On the boiler’s display, the green LED will light up and stay on, this means that the boiler’s warmstart system is now activated/switched on.

To deactivate/switch off warmstart, turn the “top” hot water control knob anticlockwise, all the way around until it stops.

The green light on the display should now go out, indicating that warmstart has been switched off. The hot water control knob will now need to be turned clockwise, until the desired temperature setting has been reached (but not turning all the way around to the end, as warmstart would be switched back on).

Please Note

You can read about warmstart for both the Vaillant ecoTEC Pro and ecoTEC Plus models in more depth, in the boiler’s “user instructions”, under the heading “Warmstart”.

If you don’t have the user instructions for your Vaillant boiler, it may be possible to download these instructions online.

Remember, people who would normally be looking for information on such things like, “How to use less gas” or “Tips on how to lower your fuel bills”, would probably not want to have their boilers Warmstart facility activated, due to the fact that they would then be burning more gas, than they actually needed to!

A "Vaillant ecoTEC annual qualifying service" is needed at the end of the 1st, 2nd, 3rd, 4th and following years, in order to keep the boiler parts and labour warranty valid throughout the guarantee period. Can Glowcare provide this service?

Yes we can, providing you live in the North West of England.

We are approved Vaillant agents and many customers use us for their Vaillant boilers’ qualifying warranty servicing through the years of the guarantee.

If you live somewhere else in the U.K., then try searching with the same information that brought you to us, you also might try putting in Vaillant Emergency Plumber or Glow-wom Emergency Gas Service Engineer, adding of course your precise location. Hopefully this will bring up details for a specialist in your area.

What are your qualifications and experience?

Glowcare are proud to be accredited as approved service agents. We are City and Guilds, time-served tradesmen, offering over 20 years of experience working independently, in the gas central heating boiler repair industry, exclusively on Glow-worm, Saunier Duval, and Vaillant boilers.

We are Gas Safe Registered (formerly Corgi Registered) and are fully qualified to work on natural and LP gas boilers. We are happy to show our customers our comprehensive list of qualifications on request.

Our expertise and continued attendance on factory training programmes ensures we can carry-out repairs on faulty, broken or leaking ultra-modern high efficiency boilers. These latest models include: Glow-worm Ultracom, Flexicom and Betacom as well as Vaillant ecoTEC pro & plus and ecoMAX pro.

Our work as approved manufacturer’s service agents for over 20 years, almost always guarantees that repairs to a customer’s boiler get completed in one single service call.

All work and parts carry a one year guarantee.

Glowcare are fully insured for up to £2,000,000 for Public Liability and have a £10,000,000 Employers Liability / Indemnity limit.

What does a boiler service comprise of and how often should my boiler be serviced?

Our boiler servicing involves a visual inspection, checking and testing the different boiler functions for correct and safe operation and cleaning out of dust and debris. See our Glowcare Boiler Service page for more details.

The most important reason for a regular boiler service is for your safety. A faulty boiler could result in poisonous carbon monoxide leakage into your home (which can be fatal).

For more information about carbon monoxide poisoning, including signs and symptoms, visit Your boiler will run far more efficiently when it has been regularly serviced, saving you money in the long-term and reducing emissions into the environment.

We recommend that your boiler is serviced annually.

Do you carry replacement parts with you?

We carry a comprehensive parts stock for your Glow-worm boiler, Saunier Duval boiler or Vaillant boiler. All parts are guaranteed for one year after installation. At Glowcare we do not place an age limit on your boiler for repair. Please check our Glow Worm, Saunier Duval or Vaillant boiler model lists to find your boiler.

What do you mean by "fair pricing"?

At Glowcare we only charge a one-off fixed labour price for diagnosing and fixing your boiler, however long the repair takes. This price also includes call-out. Should your boiler require a new part to get it up and running again this will obviously be extra, however we will always advise you of the cost of the part before the repair is started.

What should I do if I smell gas?

If you smell gas we recommend that you immediately call National Gas Emergency Service on 0800 111 999 (England, Scotland and Wales). For LP Gas you will see the gas supplier’s emergency number on the bulk storage vessel or at the meter.

Switch off the gas at the control valve to the appliance and at the mains (if you know where it is).

Open all windows and doors to ventilate the area.
Don’t create a flame and put out any naked flames.
Don’t operate electrical switches.
Keep people away from the area.

Contact a gas safe registered engineer to carry out necessary repairs.

For more information visit

My town is not on your "Areas We Cover" page, can you list where you will travel to?

We cover most areas in the North West, but for a comprehensive list of all areas that are covered by Glowcare, please visit our Postcodes and Areas Directory page.

Our Glow-worm/Saunier Duval/Vaillant gas central heating boiler has stopped working and it is displaying an "F" code fault. Can you help?

*See list below to identify your specific boiler model.

Is your boiler displaying a fault code, such as:
Glow-worm: F1, F2, F3, F4, F5, F6, F7, F8, F9, F10, F11, F12, F13, F14, F15, F16, F17, F18, F19, F20, F21, F22, F23, F24, F25, F26, F27, F28 etc.
Saunier Duval: 01, 05, 0.5, 21, F1, F2, F3, F4, F5.
Vaillant: F0, F1, F10, F11, F13, F20, F22, F23, F24, F25, F27, F28, F29, F32, F37, F42, F43, F49, F60, F61, F62, F63, F64, F65, F67, F70, F71, F73, F74, F75, F76, F78.

Fault codes can appear when the boiler has experienced, e.g. “low system pressure”, “electrical supply failure” or “no gas to the appliance”.

With the boiler manual to hand, you can check the specific “F” code to identify its meaning, then try to reset the boiler.

This may well rectify the problem.

However, you may have tried this and found that the “F” code returns.

This may indicate a more complicated boiler fault or breakdown that you will not be able to fix yourself. If this is the case then you will need an experienced Gas Safe engineer to attend and repair.

Glowcare are approved specialists for Glow-worm, Saunier Duval and Vaillant gas boilers in the North West of England. We deal with all common faults that occur. We can be contacted on 01244 880 725 or 07789 018 775 to arrange a service call.

* Glow-worm 24 CXI, 30 CXI, 38 CXI, Glow-worm 12 HXI, 15 HXI, 18 HXI, 24 HXI, 30 HXI, 38 HXI, Glow-worm 18 SXI, 30 SXI, Glow-worm 12 CI, 15 CI, 18 CI, 24 CI, 30 CI, 38 CI, Glow-worm Flexicom 24 CX, 30 CX, Glow-worm Flexicom 12 HX, 15 HX, 18 HX, 24 HX, 30 HX, Glow-worm Flexicom 18 SX, 30 SX, Glow-worm Ultracom 24 CX, 30 CX, Glow-worm Ultracom 24 CXI, 30 CXI, 38 CXI, Glow-worm Ultracom 12 HXI, 15 HXI, 18 HXI, 24 HXI, 30 HXI, 38 HXI, Glow-worm Ultracom 18 SXI, 30 SXI, Glow-worm Ultrapower 100, Ultrapower 170, Glow-worm Ultracom2 24 CXI, Ultracom2 30 CXI, Ultracom2 35 CXI, “British Gas”, BG 330, 330 Plus, Glow-worm Xtramax HE and Glow-worm XTRAFAST High Efficiency Condensing Boilers.

* Saunier Duval Thema Condens F24E, F30E. Saunier Duval Condens F24E, F30E. Saunier Duval ISO Fast Condens F35E, Saunier Duval XEON Condens F18E, F30E. Saunier Duval Thema Plus Condens F30E. Saunier Duval Enviro Plus F24E, F28E. Saunier Duval Thema Classic 24E, 30E, 35E. Saunier Duval ISO Max F28E. Saunier Duval ISO Fast F28E, F30E. Saunier Duval Protherm 80E, 100E. Saunier Duval Jaguar 80E, 100E. Saunier Duval Icon 24T, 28T.

* Vaillant ecoTEC pro 24, 28. Vaillant ecoTEC plus 937, 824, 831, 837, 612, 615, 618, 624, 630, 637, 415, 418, 428, 438. Vaillant ecoTEC Exclusive 832, 838. Vaillant ecoMAX Pro VU 186.0, VU 286.0. Vaillant ecoMAX 613/2, 618/2, 622/2, 635E, 824/2E, 835E. Vaillant TURBOmax pro 24 E, 28 E, TURBOmax plus 824 E, 828 E, VUW242/2-5 R1…R3.

Disclaimer – Important information relating to the help and advice on this website
Our aim on this website ( is to provide homeowners and private landlords with advice that is as reliable and helpful as we can. However, please note that this is guidance only. It does not necessarily deal with all important topics or cover all aspects of the topics with which it deals, and may not be relevant or appropriate in all circumstances. Its purpose is not to provide professional advice and therefore should not be relied on as such. If you are in any doubt, you should always consult an appropriately qualified expert for specific advice before acting on any of the information contained on this website. At no time should you attempt to carry out any activity which may put you or anyone else at risk, or which may cause damage to your property or anyone else’s property. The activities described should not be attempted by anyone who is under the age of 18, or inexperienced. Some activities such as those that involve gas or electricity should only be carried out by qualified professionals. Always read and follow relevant manuals and safety instructions. Also, if you have insurance cover, you should check that your cover is not invalidated by undertaking any work yourself.