Vaillant ecoTEC Plus Problems — Faults F22, F75, F28 & Fixes
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The Vaillant ecoTEC Plus is a workhorse boiler found in thousands of UK homes, but like any hard-working piece of kit, it can develop faults. Most problems with this model fall into a handful of well-understood categories — low pressure, sensor issues, ignition failures, and diverter valve troubles — and the good news is that many are straightforward to diagnose. Whether you're renting, own your home, or manage a property portfolio, understanding what these fault codes mean and when you can take simple action yourself (like topping up the pressure) versus calling a Gas Safe engineer will save you time, stress, and money. This guide walks through the most common ecoTEC Plus faults, what causes them, and how to fix or troubleshoot them safely. If you smell gas at any point, leave the property immediately and ring the national gas emergency number.
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Most likely cause & what to check
The Vaillant ecoTEC Plus (418, 424, 428, 430, 435, 438) is one of the UK's most widely installed boilers, particularly in new-build homes and rental properties from the 2010s onward. It is generally reliable but has a few well-known issues worth knowing about. Manuals and fault codes at vaillant.co.uk or call 0330 100 3461.
Fault code F22 (low water pressure — most common ecoTEC Plus fault): the display pressure should read 1–1.5 bar. Use the filling loop (a braided silver hose under the boiler with two valves) — slowly open both until the display shows 1.2 bar, then close both firmly and press reset. If F22 returns within a week, there is a leak somewhere in the system.
Fault code F75 (pressure sensor or pump fault — notorious on ecoTEC Plus): F75 appears when the pump runs but the pressure sensor doesn't detect a pressure change — either the sensor is faulty, or the pump has failed. Crucially, the pressure gauge may look fine. F75 cannot be fixed by the homeowner — a Gas Safe engineer will need to test and likely replace the pressure sensor (a common inexpensive fix) or the pump.
Fault codes F28 / F29 (ignition failure / flame loss): F28 means the boiler failed to light. F29 means it lit but the flame went out. Reset once each. In winter, check whether the condensate drain pipe outside is frozen — a blocked condensate pipe is the most common cause of F29 in cold weather and can be fixed by carefully pouring warm water over the frozen section of pipe outside.
Heating but no hot water (or vice versa): on a combi ecoTEC Plus this points to a diverter valve fault. The valve is inside the boiler and can be cleaned or replaced by a Gas Safe engineer — it is a relatively common and inexpensive repair on this model.
Scale build-up (418 model in hard water areas): the ecoTEC Plus 418 in particular can suffer from heat exchanger scaling in hard water areas, causing kettling noises and F75-type faults. A system filter (Fernox TF1 or similar) fitted at service is the best prevention. If scaling has already occurred, a chemical flush is needed.
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Frequently asked questions
Can I fix a Vaillant ecoTEC Plus fault code myself?
You can safely handle F22 (low pressure) by using the filling loop to top up the system to 1.2 bar, and you can unfreeze a condensate drain pipe in winter. However, fault codes like F75 (sensor or pump fault), F28/F29 (ignition issues that won't reset), and diverter valve problems require a Gas Safe registered engineer — attempting repairs on these risks both your safety and your warranty.
What does fault code F22 mean and how do I fix it?
F22 means water pressure in your heating system has dropped below safe operating level (it should sit between 1–1.5 bar). Locate the filling loop — a silver braided hose with two valves beneath the boiler — slowly open both valves until the pressure gauge reads 1.2 bar, then close firmly and press reset. If F22 returns within a week, you likely have a leak and should contact a plumber.
Why does my Vaillant ecoTEC Plus boiler keep showing F75?
F75 signals a fault with the pressure sensor or the circulating pump — the pump is running but the sensor isn't detecting a pressure change as it should. The pressure dial may look normal, which is why this fault is tricky; a Gas Safe engineer will need to test and replace whichever component has failed, usually the sensor (an inexpensive fix) or occasionally the pump.
My boiler is heating the house but not providing hot water — what's wrong?
On a combi ecoTEC Plus, this typically points to a faulty diverter valve inside the boiler, which routes hot water between the heating circuit and the tap supply. The valve can sometimes be cleaned but often needs replacing — it's a recognised weak point on this model and a relatively straightforward job for a Gas Safe engineer.
My Vaillant boiler won't light in cold weather — what should I do?
Reset the boiler once by pressing the reset button. If it still won't light (F28) or lights then cuts out (F29), check outside whether the white plastic condensate drain pipe is frozen or blocked — this is the most common cause in winter. Carefully pour warm (not boiling) water over the frozen section to thaw it, then try resetting again.
Is the Vaillant ecoTEC Plus 418 prone to problems in hard water areas?
Yes — the 418 model can suffer from scale build-up in the heat exchanger in hard water regions, leading to kettling noises and F75-type faults. The best prevention is fitting a system filter (such as a TF1) at your boiler's annual service; if scaling has already occurred, a chemical flush from a plumber is needed to restore performance.