F75 on a Vaillant boiler is a pump water shortage fault: the pressure sensor sees no adequate pressure rise when the pump starts, so the boiler locks out. Diagnosing it means looking at the pump, the pressure sensor and the sealed system, which is work for a Gas Safe registered engineer. F22 is the related low water pressure code, and you can often top the system up yourself through the filling loop. F28 points to no flame signal during ignition, and F62 is defined in the installation and maintenance instructions for your specific model. This page sets out what each code means, what you may check safely and where the line to gas work sits.
What does the F75 fault code mean on a Vaillant boiler?
F75 on a Vaillant boiler is a pump water shortage fault. Vaillant lists the code in its official fault code table. The boiler's pressure sensor does not detect a sufficient pressure rise when the pump starts. The appliance then shuts down rather than firing.
F75 is not simply a gauge reading a little below the green band. The pump, the pressure sensor and the expansion vessel are involved. The expansion vessel is the sealed tank that takes up the swelling of heated water. All of these sit inside the boiler casing or in the sealed pipework, so checking them is work for a Gas Safe registered engineer.
One thing helps before you call. Read the pressure gauge with the heating switched off and note the figure. That reading tells the engineer whether the system is genuinely low on water, or whether the pressure looks normal and the fault sits with the pump or the sensor.
F22 on a Vaillant boiler: low water pressure you can often top up
F22 means the water pressure in the system has dropped below the normal range of 1 to 1.5 bar. Vaillant's remedy is to refill the system through the filling loop until the gauge sits between 1 and 1.5 bar. The filling loop is the short braided hose with a valve at each end, usually under or near the boiler.
Vaillant sets out the order of work for householders. Switch the boiler off and let the system cool. Find the filling loop and watch the pressure gauge as you open the valves. Close both valves again once the needle sits in the green band.
Stop if the pressure does not rise. Vaillant's advice is to close the filling loop straight away and call a Gas Safe registered engineer, because opening the boiler casing is dangerous and belongs to the engineer. Pressure that keeps dropping week after week points to a leak or a failed expansion vessel. Our guide on low boiler pressure explains what the gauge is telling you.
F22 or F75: which Vaillant pressure code can you act on?
F22 is the code you can often clear yourself; F75 is not. Both codes involve pressure, but they describe different measurements taken by the boiler.
- F22 – the system pressure sits below the normal 1 to 1.5 bar range. Refilling through the filling loop is a householder task under Vaillant's own advice.
- F75 – the pressure sensor detects no adequate rise when the pump runs. The cause sits with the pump, the sensor or the sealed system, and diagnosis belongs to a Gas Safe registered engineer.
- Both returning repeatedly – a recurring loss of pressure suggests a leak or a failed expansion vessel, which needs an engineer rather than another top-up.
Topping up a system that keeps losing water masks the real problem. Note how often you refill and tell the engineer. That pattern is useful evidence during a repair visit.
Why does a Vaillant boiler show F28?
F28 means the flame signal was not detected during the ignition phase. Vaillant describes it as a failure to light at start-up. The boiler tries to fire, sees no flame and locks out for safety.
Vaillant names several causes: air in the gas line, gas supply pressure that is too low, a faulty gas valve assembly, and a disturbed gas path caused by recirculation or a blocked flue. Every one of those is gas or flue work. None of them is something you check, adjust or clear yourself.
Vaillant also lists a frozen condensate pipe among the triggers for F28 and F29. That is why the code often appears during a cold snap. Report it when you call, because it helps the engineer plan the visit.
What does F62 mean on a Vaillant boiler, and where is it defined?
F62 is defined in the installation and maintenance instructions for your specific Vaillant model, under the overview of fault codes. The meaning is not the same across every appliance, so the model number on the data badge matters. An ecoTEC plus and an ecoTEC exclusive are documented separately.
Do not assume a particular part has failed because F62 appears. Guessing at a component leads to the wrong repair and wasted money. A Gas Safe registered engineer reads the code against the manual for your model and tests from there.
Have the model name and serial number ready when you call. Both are printed on the label behind or under the boiler's front panel, visible without removing anything. That detail lets the engineer check the right fault table before arriving.
What can you check yourself when a Vaillant fault code appears?
Four checks belong to you, and Vaillant draws the same line. Beyond refilling pressure and bleeding radiators, fault codes are for a Gas Safe registered engineer.
- Boiler pressure – read the gauge with the heating off. It should sit between 1 and 1.5 bar, and it rises during operation as heated water expands, which is normal.
- Thermostat and programmer – a target temperature already reached is a common reason a boiler will not fire. Set the target above room temperature, check the time programme after a power cut, and check the thermostat batteries.
- The reset button – usually near the display, sometimes a dial, marked with a flame and a line through it. Hold it for about three seconds. Some appliances need several minutes or a second attempt.
- Bleeding radiators – switch the heating off and let the radiators cool for one to two hours. Use a bleed key, a cloth, gloves and a container, and close the valve once water appears.
Anything touching gas, the flue, seals, the condensate inside the appliance or the boiler casing is not on that list. It is work for a Gas Safe registered engineer. If a code returns after one reset, stop resetting and book a repair. Our guide on what to do when your boiler has stopped covers the same ground for other faults.
Who is allowed to work on your boiler after an F75 or F28 lockout?
In England, anyone working on a gas appliance in a home must be Gas Safe registered and competent for that type of work. The duty comes from the Gas Safety (Installation and Use) Regulations 1998, as amended. HSE states that it is against the law for anyone else to carry out the work. The competences held by an engineer are printed on the back of the Gas Safe ID card.
HSE is equally clear about suspect appliances. A gas appliance thought to be unsafe must not be used, and should be left alone until a Gas Safe registered engineer has checked it. Repeatedly pressing reset on a boiler that keeps locking out works against that advice. HSE also recommends that gas appliances, flues and pipework are checked at least once a year by a Gas Safe registered engineer.
FM Power is Gas Safe registered and covers London and the surrounding counties. You get a written fixed price before any work starts, and there is no monthly contract. If F75, F28, F22 or F62 keeps coming back on your Vaillant, our boiler service and repairs page is the place to arrange a visit.
Sources
- Vaillant – Boiler fault codes list
- Vaillant – Understanding an F28 fault code on a Vaillant boiler
- Vaillant – What pressure should my boiler be?
- Vaillant – How to repressurise a boiler
- Vaillant – What do I do if my boiler has no pressure
- Vaillant – How to reset a boiler
- Vaillant – Boiler not igniting? Common issues
- Vaillant – How to bleed a radiator
- Vaillant – ecoTEC exclusive installation and maintenance instructions (PDF)
- HSE – Gas safety: home owners
- HSE – Domestic gas
- legislation.gov.uk – Gas Safety (Installation and Use) Regulations 1998