Vaillant Boiler Not Working — Fault Codes & Fixes
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Vaillant boilers are reliable workhorses found in thousands of UK homes, but like any heating system, they occasionally display fault codes when something needs attention. These codes—F22, F28, F29, F75 and others—are your boiler's way of telling you what's gone wrong, and they range from simple fixes you can handle yourself (like topping up pressure) to issues that require a qualified Gas Safe engineer. The good news is that most Vaillant faults are straightforward to diagnose once you understand what each code means. This guide walks through the most common fault codes, what triggers them, and whether you can fix it yourself or need to call a professional. If you ever smell gas, however, stop immediately and ring the National Gas Emergency Service on 0800 111 999—don't attempt any repairs yourself.
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Most likely cause & what to check
Vaillant ecoTEC boilers (ecoTEC plus, ecoTEC pro, ecoFIT) are one of the most common boilers in the UK. When a fault occurs, a code appears on the display. Full fault code guides are available at vaillant.co.uk or by calling Vaillant customer support on 0330 100 3461.
Fault code F22 (low water pressure): this is the most common Vaillant fault. The pressure gauge or display should show 1–1.5 bar. If it's below 1 bar, use the filling loop to top up (look for two small valves underneath the boiler — turn both anti-clockwise until pressure reaches 1.2 bar, then turn back clockwise). If pressure drops repeatedly, there is likely a leak — call an engineer.
Fault code F28 (ignition failure): the boiler failed to light. Reset by pressing and holding the reset button (marked with a curved arrow) for 3 seconds. Check that other gas appliances are working. If F28 returns repeatedly, there may be a fault with the ignition electrode, gas valve, or gas supply — a Gas Safe engineer is needed.
Fault code F29 (flame loss during operation): the boiler lit but the flame went out unexpectedly. This can be caused by a faulty flame sensor, intermittent gas supply, or condensate pipe blockage in cold weather. Check the condensate drain outside isn't frozen. Reset once — if it returns, call an engineer.
Fault code F75 (pressure sensor or pump fault): this fault appears even when pressure looks correct, because the sensor that detects pressure change when the pump starts is faulty — or the pump itself has failed. This requires an engineer as it is not a user-resolvable fault.
Vaillant boilers carry a manufacturer's warranty (up to 7 years when registered within 30 days of installation). Contact vaillant.co.uk for warranty claims. For out-of-warranty repairs, any Gas Safe engineer can service Vaillant boilers — parts are available from all major plumbers' merchants.
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Frequently asked questions
What does fault code F22 mean on my Vaillant boiler?
F22 indicates low water pressure—the most common Vaillant fault. Your pressure gauge should read between 1 and 1.5 bar; if it's dropped below 1 bar, the boiler shuts down as a safety measure. You can usually fix this yourself using the filling loop (two small valves beneath the boiler) to restore pressure to 1.2 bar.
Can I fix a Vaillant boiler fault code myself or do I need an engineer?
It depends on the fault. F22 (low pressure) is often user-resolvable using the filling loop, and F28/F29 can sometimes be fixed with a simple reset. However, F75, repeated fault codes, and anything involving the gas supply, ignition, or internal components require a Gas Safe registered engineer—it's a legal requirement and a safety issue.
Why does my Vaillant boiler keep showing F29 (flame loss)?
F29 means the boiler lit but the flame went out unexpectedly—often caused by a blocked condensate pipe (especially in freezing weather), a faulty flame sensor, or an intermittent gas supply. Check that your external condensate drain isn't frozen or blocked; if the fault persists after one reset, contact an engineer.
My Vaillant shows F75 even though the pressure looks normal—what's wrong?
F75 indicates a fault with the pressure sensor itself or the circulation pump, not necessarily a pressure problem. The sensor detects pressure changes when the pump starts; if it's faulty, it will trigger F75 regardless of actual pressure. This requires an engineer to diagnose and repair.
Is my Vaillant boiler still under warranty and how do I claim?
Vaillant boilers carry a manufacturer's warranty of up to 7 years if you registered the boiler within 30 days of installation. Contact vaillant.co.uk or call their customer support on 0330 100 3461 to check your warranty status and make a claim for covered repairs.
What should I do if I see fault code F28 (ignition failure)?
F28 means the boiler failed to ignite. First, check that other gas appliances in your home are working (to rule out a gas supply issue), then press and hold the reset button (marked with a curved arrow) for 3 seconds. If F28 returns repeatedly, there's likely a fault with the ignition electrode, gas valve, or gas supply—you'll need an engineer.