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Common Vaillant Boiler Faults [And What To Do Next]

Like all boilers, common Vaillant boiler faults need to be diagnosed via troubleshooting. It’s important to understand that all work should be completed by a Gas Safe boiler engineer.

Consider getting an expert to quote the repair cost.

Once repairs creep towards £500 and beyond, with boilers that are out of warranty, we’d look towards a replacement rather than a repair. You can get on screen prices here from Heatable, or read our guide that covers the cost of a new boiler.
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Many quick fixes are just that; boiler faults will keep appearing until the root of the fault is diagnosed and fixed. And understanding the fault code is the first part of the process.

If you already know what the fault code for your Vaillant boiler is, click through to the relevant section.

Vaillant F22 Boiler Fault

One of the most common Vaillant boiler problems is the F22 fault code. This problem is common on the Ecotec Plus and Ecotec Pro models, in particular the Vaillant Ecotec Pro 28.

This code is connected to a lack of pressure, or water.

Most newer boilers have sensors that will constantly measure the pressure of the water in the system. If there is a pressure drop, the sensors kick in and display an error code.

You may find that there is a red light on the display board. This is simply a clarification that the boiler is not firing correctly.

The F22 fault code will automatically put the boiler into a limp mode, much like a car would if the ECU detects a problem.

If it continues firing without enough water, it could damage expensive parts within the boiler.

Fixing a Vaillant F22 Boiler Fault

Many websites suggest that a simple fix is using the filling loop to top up the pressure on your Vaillant boiler.

Whilst this in theory is correct, it doesn’t fix the problem. A boiler doesn’t just lose pressure for no reason, so the fault needs to be fixed.

Boilers tend to sit at 1.5 bar of pressure. If it has dropped below this, topping up via the filling loop is only likely to cause further damage.

Your system should be dosed with inhibitor, and by topping up the boiler’s pressure using the filling loop, you are diluting the chemicals that are protecting the system.

A Gas Engineer will need to troubleshoot the boiler to determine whether the F22 fault is related to:

  1. Lack of pressure
  2. Lack of water
  3. Both of the above

Leaks are one of the most common reasons a boiler loses pressure (and water). They can come from radiators, towel rails, radiator valves, pipe work, air vents or even expansion vessels.

Another common cause is a build-up of air in radiators.

However, a faulty pump could also be the culprit. A lot of older Vaillant boilers used Wilo pumps. They are prone to faults and over time they seize or start to leak. This would be the cause of low pressure and lack of water.

Vaillant F27 Boiler Fault

The next common Vaillant boiler fault we come across is the F27 fault code. The boiler’s sensor has noticed that the flame is not correct.

This could be for one of several reasons:

  1. The PCB is not working correctly, and the flame is working fine.
  2. The gas valve is not working correctly, and therefore, the boiler is not getting the correct amount of gas to produce the correct flame.
  3. The flame sensor is detective and needs replacing.

In some cases, the boiler doesn’t fire at all. In this instance, a likely cause is ignition leads.

Fixing a Vaillant F27 Boiler Fault

This is certainly not one of the easy Vaillant boiler faults to troubleshoot.

A Gas Engineer will need to come and inspect the boiler and its internal components to diagnose the problem.

Where the fault relates to anything but the PCB, usually replacing the parts is the most economical option (assuming the rest of the boiler looks like it is in good condition).

Like many boiler faults, if it relates to the PCB, it’s usually much more economical to fit a new boiler.

The cost of a PCB and labour for installation can be as much as £500. For an old boiler that is not likely to last more than a few years, replacing the PCB is certainly not the best option. And you can get prices for a new boiler within 90 seconds, using Heatable’s handy quote form.

Vaillant F28 & F29 Boiler Fault

The Vaillant F28 boiler fault code is not as common as the F22 or F27. And the F29 code will be displayed after similar symptoms are shown to the F28 fault code.

This fault code will usually be displayed after you experience a boiler lockout, and you have no supply of heating or hot water.

It relates to one thing; lack or no supply of gas.

Fixing a Vaillant F28 & F29 Boiler Fault

Being a gas related fault, you shouldn’t try to attempt to fix this problem yourself. Always call a Gas Engineer.

From a fault troubleshooting point of view, you can try one thing.

If you have any other gas appliances (such as a hob), check that they work.

It’s an unlikely scenario, but it could be a problem with the gas supply (meter has run out, supplier has cut off the gas or repairs to gas main in your road).

If this is not the issue, a Gas Engineer will be able to start their troubleshooting process by analysing:

  1. Gas valve operation and adjustment settings
  2. Condition of the ignition leads
  3. Condition and operation of the ignition unit
  4. Check the air inlet duct

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Vaillant F75 Boiler Fault

Out of all the Vaillant boiler faults we come across, the F75 fault code is the most common. It’s particularly common on the Eco Tec Plus range and the Eco Tec Pro 28.

The Vaillant service manual will list the following error in relation to the F75 fault code.

“Water pressure sensor and/or pump defective, air in heating installation, too low pressure in boiler; connect external expansion vessel to return.”

So what you have here is three possible fault scenarios:

  1. The boiler’s central heating pump
  2. The boiler’s pressure sensor
  3. Both above are faulty

Fixing a Vaillant F75 Boiler Fault

I’ll say right now, the most common cause of the F75 fault is the pump. And there is a good reason for that.

Most newer Vaillant boilers use top quality Grundfos pumps. However, this has not always been the case.

Older Vaillant boilers used to use Wilo pumps. They are known for being extremely unreliable. In fact, they are probably the component most likely to break in these older boilers.

You can do a quick manual check of the pump on your Vaillant boiler by starting up the heating, or running the hot water.

After the boiler fires up, you’ll hear a gentle humming noise. So, everything being well, this should be the noise of the pump circulating the water through your pipework and radiators.

If there is no sound after starting up the boiler, there’s a good chance that the pump is the cause.

Older Wilo pumps ended up getting seized bearings (especially after a long period of non-use) and a replacement is the best option.

The other scenario is that it’s the pressure sensor causing the F75 boiler fault.

Like the Wilo pumps, the older Vaillant pressure sensors were not particularly durable. In fact, they were revised 3 times over a short period.

Heating systems have a lot of debris build up (carbon and sludge) over time. This can block the pressure sensor and cause it to be defective.

A Gas Engineer will be able to diagnose the boiler fault and take the appropriate action.

If you need to replace the pump, it’s likely to cost just under £300.

For the pressure sensor, the cost will be just under £250.

What’s Next?

Need help from qualified engineers? > Click Here <.

Looking to replace your boiler? Jump over to Heatable’s clickable form and get boiler prices on screen in minutes (no personal details needed).

Or, if you have a Vaillant boiler fault not listed, please use the comments and we’ll get back to you as soon as possible.

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  1. I have a Vaillant Ecotec Combi which works well in producing hot water on demand and providing heating, with no error codes. However even when I am not calling for heat or hot water l can hear it running for a brief cycle every now and again. Is this ok?

  2. water pressure gauge is running into max red but working ok have bleed it but returns into the red within a couple of hours

    1. Hi Pete. Is it returning to red on without heating on? Or only when the heating is on? We’ve seen filling loops been defective in the past. I’d suggest getting an engineer out to avoid causing any damage.

  3. Hi my water pressure has gone to the fill line and it says it is 3.7 and it is flashing on and off .My heating is on should I be worried thanks

  4. Hi my vaillant ecotec keeps displaying an F75 fault, if i increase pressure slightly it will work fine for a while. This suggests a leak or drop in pressure, however the internal gauge reads halfway which is where it should be, but the digital display reads 3 Bar.

  5. We have a brand new ecotech plus fitted however we have a peculiar problem. With everything turned of it will run the radiators continually at full heat, ie all night when the timer is off and the temperature sensor is set to 10 *. You can imagine our gas bill! The gentleman who fitted it keeps checking the obvious and says it is ok, patently it is not. Any ideas?
    Thanking you in advance.

  6. The fan starts running when cold water taps are turned on.If
    I reduce peessure to a trickle this does not happen.Is there a fault ?

  7. I have an Eco Tec 837 combi and when the central heating i on the pressure goes up to 2.9 within about 15 minutes.
    There is no water coming out of the shraeder valve and the pressure in expansion vessel is 1 bar. there is no latent heat in the small pipe to the expansion vessel or on the water side. Could there be a blockage that is preventing ther expansion vessel working or could there he another issue?

    1. Hey David,

      Sounds like a pressure release issue, so likely the expansion vessel is either faulty, or needs pressurising.

      Thanks

  8. Got a Ecotec 831 plus just had new pump new fan new plate heat exchanger new prv got good hot water but heating some rads hot some rads Luke warm some cold have bled all rads turned them all off gone round got them all going one by one so no blockage also had power flush any ideas please

  9. We have a brand new valiant eco tech plus 615 everything is working ie heating and hot water but every so often it makes an alarming vibrating noise and the only way to stop it is to turn the boiler off and turn it on again the people that fitted it have asked us to record the noise because they are not sure of the fault
    Please have you any ideas
    Regards john

  10. I have a valiant eco pro28 it turned off when I turned it back on when pump went to kick in it turned its self off again I’ve changed pump but it’s still doing the same thing is it the circuit board as no fault is coming up

  11. I have a Vaillant ecotec 24.
    We had a brief power outage this morning and since then the hot water works fine but we have no central heating.
    There are no errors displayed.

  12. Hi.

    I have a four year old ecoTEC pro 28 vaillant combi boiler which has been operating without any problems throughout the last four years.
    Suddenly it has developed a problem.
    The hot water and heating modes can be operating fine then i find that the digital display panel is not illuminated and shows no display at all. it is totally blank.
    I switch the electrical supply off for a few moments, with the heating turned down, then switch the power back on and press the reset buttons and the boiler, including heating will come back on and the radiators heat up.

    This has happened approximately six times in the last twenty four hours and the display has never displayed a fault code. It just shows its normal operating and setting display or apparently loses all its power and is blank.
    There is no fault on the power supply to the boiler and the condense line is free and operating correctly.
    Do you have any suggestions and is this possibly a historic situation with these boilers?
    Kindest Regards
    Grahame

  13. I have a Vailliant eco Tec plus 630 connected to a presurised hot water cylinder. Every two or three days I have to top the boiler up with water. However, when I top up the water to 1.5 bar, once the boiler comes on the pressure continues to increase to 3 bar. I then have to relieved the pressure by taking water from one of the radiators. I do this until the pressure is below 2 bar. Then over night when the boiler is not operational the pressure sometimes falls below 0.3 and then the boiler doesnt start up. The hot water heats up just fine by the boiler when its working but obviously the boiler is not working correctly because i didnt have to fiddle with the water in the past. What do you think might be the likely problem and what should I do. Kind regards Richard

    1. Hey Richard. Sounds like a pressure release/air vent fault. Your boiler should hover around 1.5…maybe up to 1.7 ish when on. But as it’s not being vented it’s shooting to 3. By releasing water, you’re removing pressure, so when it all cools down that’s why it’s gone from 1.5 – 0.3.

      Have a look here. An boiler engineer will be able to fix that pretty-easily.

      https://heatingforce.co.uk/blog/boiler-losing-pressure/

  14. Hi I m Asif, I hv jst got installed brand new boiler eco fit it’s called abt 6 weeks ago, it works completely fine but everytime if I hv to put heating on or if I use hot water it jst make ‘tuk’ ‘tuk’ loud noice, it make noise few time as soon as I put heating on, I don’t know why, I near known any boiler make noice like that , when I check with installer he said it’s normal, but to me it doesn’t sounds normal , pls help

    1. Are you talking about noise in the thermostat? Because that’s how they usually work when they send signal to the boiler to start.

  15. Hi Guys,
    My 2yo “Vaillant Ecotec Pro” works great, however when i use 1 of 4 hot taps (only 1 draining ) which are all on the same pipe the pressure drops and the hot water dries up/stops.
    How can that happen with only 1 out of 4 taps ? Any input will be greatly appreciated

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