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Vaillant F28, F29 and F22 fault codes: what they mean and what to do
F28 and F29 mean your Vaillant can’t light or keep its flame. F22 means the water pressure has dropped too low. Here’s what to check, how to reset it and when to call an engineer.
- F28no flame when lighting
- F22pressure below 0.5 bar
- 3resets, then call an engineer
F28ignition fault
Vaillant’s ecoTEC and ecoFIT boilers show an F followed by a number when something’s wrong. F28, F29 and F22 are the ones we get called about most, especially once the weather turns.
The good news is that all three have checks you can do yourself first. Here’s what each one means.
F28 and F29
The boiler can’t light, or can’t keep its flame.
What do they mean?
F28 means no flame was detected while the boiler was trying to light. F29 means the flame went out while it was running and it couldn’t relight. Either way, it’s locked itself out to stay safe.
Common causes
- Not enough gas reaching the boiler
- No credit on a prepayment meter
- A blocked or frozen condensate pipe
- A faulty ignition electrode or control board
- A problem with the flue
Checks you can do
See if your other gas appliances work. Top up a prepayment meter if it’s run out. In a frost, check the condensate pipe outside for ice. Beyond that, Vaillant says it’s a job for an engineer.
Fault finding
How to reset a Vaillant
Once you’ve checked the gas and the condensate pipe.
Fix the cause first
Top up the meter or thaw the pipe before resetting. Resetting with the cause still there won’t help.
Press reset for one second
Find the reset button on the front panel and press it for about a second. The boiler will try to light again.
Up to three tries
Vaillant’s manuals say if it still won’t light after three reset attempts, call a competent engineer. Don’t keep going.
Book a repair
If F28 or F29 keeps coming back, something needs looking at. A repair visit is £120 including VAT, before any parts.
F22: low water pressure
Usually something you can top up yourself.
F22 means the pressure in your heating system has dropped below 0.5 bar, so the boiler has switched off to protect itself. Vaillant says you can top it up yourself if you’re confident doing it.
- Let the boiler cool down
- Find the filling loop, usually under the boiler
- Open it slowly and watch the gauge
- Stop at 1 to 1.5 bar and close it
On the ecoTEC plus, the low pressure warning clears from the display about 20 seconds after you’ve topped up.
When F22 is a job for us
If the gauge reads over 1 bar but F22 still shows, it’s likely a sensor fault. Leave the casing on and book a repair. And if you’re topping up often, water’s escaping somewhere. See our losing pressure guide.
Checking pressure
Never open the casing
Vaillant advises strongly against going inside the boiler. Everything on this page is done from the outside.
What should I do next?
- F28 in a frost, with gurglingThaw the pipe
Then press reset.
- F22, pressure under 1 barTop it up
1 to 1.5 bar, cold.
- Three resets and still F28Book a repair visit
£120 including VAT, before any parts.
- Other Vaillant codesFault code list
The common ones explained.
Common questions
What is F28 on a Vaillant boiler?
No flame was detected while the boiler was trying to light, so it’s locked out. Check your gas supply, your meter credit and the condensate pipe, then reset.
What’s the difference between F28 and F29?
F28 happens while the boiler is trying to light. F29 happens when the flame goes out while it’s running and it can’t relight. The checks are the same.
How do I reset a Vaillant boiler?
Press the reset button on the front for about a second. Vaillant’s manuals say that if it hasn’t relit after three attempts, you should call a competent engineer.
What pressure should my Vaillant be?
Between 1 and 1.5 bar when the system is cold is a safe figure for most Vaillant boilers. Your manual gives the exact range for yours.
Can I fix F22 myself?
Usually, yes. Top the pressure up through the filling loop to 1 to 1.5 bar. If the gauge already reads over 1 bar and F22 still shows, book an engineer.
Why does my Vaillant keep showing F22?
Water is getting out somewhere: a leak on the pipework, a radiator valve, the pressure relief valve, or a faulty expansion vessel making the relief valve let water out. Topping up keeps it going, but the leak needs finding.
Related pages
Sources: Vaillant, boiler fault codes; Vaillant, understanding F28; Vaillant ecoTEC plus operating instructions. Checked 2 November 2026.
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