Vaillant fault codes start with F (F22, F.28, F75 and so on). The ones you can usually fix yourself are F22 (low water pressure: top up and reset) and sometimes F28/F29 (ignition or flame loss: check gas and a frozen condensate pipe, then reset). Most other codes, like F61, F62, F63, F70, F73, F75, F83 and F84, point to a faulty part or sensor and need a Gas Safe registered engineer.
Use the table to look up your code, then jump to the full guide where we have one. This list covers the Vaillant ecoTEC range (ecoTEC plus, pro and exclusive) found in most UK homes. Glow-worm boilers, made by the same group, use many of the same codes. For other brands, see our heating guides.
Vaillant fault codes: quick reference
| Code | What it means | Can you fix it? | What to do |
|---|---|---|---|
| F22 | Low water pressure (dry fire) | ✅ Usually | Top up to ~1.5 bar, reset. Full F22 guide |
| F23 | Flow/return temperature difference too big | ⚠️ Sometimes | Check pressure, bleed radiators; else engineer |
| F24 | Temperature rising too fast | ⚠️ Sometimes | Check pressure, bleed radiators; else engineer |
| F28 | Ignition failure on start-up | ⚠️ Sometimes | Check gas, condensate pipe, reset. Full F28 guide |
| F29 | Flame lost during operation | ⚠️ Sometimes | Same checks as F28 |
| F32 | Fan fault | ❌ | Engineer (check flue isn't blocked) |
| F61 | Gas valve control fault | ❌ | Engineer |
| F62 | Gas valve shut-off delay | ❌ | Engineer |
| F63 | EEPROM (memory) error | ❌ | Engineer (often PCB) |
| F70 | Invalid device ID (PCB/display mismatch) | ❌ | Engineer; common after a part is replaced |
| F73 | Water pressure sensor signal too low | ❌ | Engineer (sensor or wiring) |
| F74 | Water pressure sensor signal too high | ❌ | Engineer |
| F75 | No pressure change detected when pump starts | ⚠️ Sometimes | Check pressure and top up; else pump/sensor fault |
| F83 | No temperature change at burner start | ⚠️ Sometimes | Check pressure, bleed air; else sensor fault |
| F84 | Flow/return sensor readings implausible | ❌ | Engineer (sensors) |
"Can you fix it?" means things a householder can safely do from the outside of the boiler: top up pressure, bleed radiators, thaw a condensate pipe, check the gas supply and press reset. Anything inside the casing is an engineer job.
Never remove your boiler's casing. By law, work on gas appliances must be carried out by a Gas Safe registered engineer. If you smell gas, call 0800 111 999 immediately.
Pressure and water codes: F22, F23, F24, F75, F83
These codes all relate to water circulation, and low pressure or air in the system is behind many of them.
- Check the pressure gauge or display. Vaillant says the gauge should generally read 1–1.5 bar.
- If it's low, top up with the filling loop to about 1.5 bar (how to top up).
- If radiators are cold at the top, bleed them, then re-check the pressure.
- Press reset.
If the code comes back with good pressure, the pump, pressure sensor or temperature sensors are likely at fault. F75 in particular often means a pump or pressure sensor problem once low pressure has been ruled out.
Ignition and flame codes: F28 and F29
F28 means the boiler couldn't light; F29 means the flame went out while running. Check that other gas appliances work, that a prepayment meter has credit, and, in cold weather, that the condensate pipe outside isn't frozen. Then reset. Full steps are in our Vaillant F28 guide.
Gas valve, fan and electronics codes: F32, F61, F62, F63, F70, F73, F74, F84
These indicate a faulty component (fan, gas valve, sensors or the circuit board). Resetting may clear them temporarily, but they'll return until the part is repaired. Book a Gas Safe engineer, and tell them the exact code.
How to reset a Vaillant boiler
- Fix the cause first where you can: low pressure, gas supply, frozen condensate pipe.
- Press the reset button on the front of the boiler. On ecoTEC models it's marked with a reset symbol; hold it for a second or two.
- Wait while the boiler runs through its start-up checks.
- If the code returns, don't keep resetting. Note the code and call an engineer.
On most Vaillant ecoTEC boilers you can see the current pressure and the last fault codes on the display. Your user manual shows how. Giving an engineer the fault history speeds up diagnosis.
What does the egg timer symbol mean on a Vaillant boiler?
A flashing egg timer (hourglass) symbol usually isn't a fault. It means the boiler is in a short waiting or anti-cycling period, pausing briefly between burns to avoid switching on and off too often. It should clear on its own within a few minutes. If it appears constantly and the house isn't warming up, the boiler may be short-cycling, which an engineer should look at.
Vaillant boiler not firing up but no fault code?
- Check the timer or programmer is calling for heat, and the room thermostat is set above the current room temperature.
- Check the boiler has power (display lit) and the fused spur switch is on.
- Check the pressure is between 1 and 1.5 bar.
- For no hot water only, check the hot water temperature setting hasn't been turned down.
If everything looks right and it still won't fire, call an engineer.
How much do Vaillant repairs cost?
| Repair | Typical UK cost |
|---|---|
| Call-out and diagnosis | £60–£120 |
| Ignition electrode | £80–£180 |
| Pressure sensor | £100–£200 |
| Expansion vessel re-charge / replacement | £60–£350 |
| Pump | £200–£400 |
| Fan | £200–£350 |
| Gas valve | £250–£450 |
| PCB | £300–£500 |
Vaillant boilers often come with long manufacturer warranties, provided they're serviced every year, so check yours before paying for parts.
FAQs
What are the most common Vaillant fault codes?
F22 (low water pressure) and F28 (ignition failure) are by far the most common in UK homes, followed by F29, F75 and F83.
How do I reset my Vaillant boiler?
Fix the cause if you can (for example top up low pressure), then press and briefly hold the reset button on the front of the boiler.
What does F75 mean on a Vaillant boiler?
F75 means the boiler didn't detect the expected change in water pressure when the pump started. Check and top up the pressure first; if F75 returns, the pump or pressure sensor probably needs replacing by an engineer.
What does F83 mean on a Vaillant boiler?
F83 means the boiler didn't see a temperature change at its flow and return sensors when the burner started, usually because of low water or air in the system, or a faulty sensor.
What does F61 mean on a Vaillant boiler?
F61 points to a gas valve control fault, which is an engineer repair. Don't keep resetting the boiler.
Do Glow-worm boilers use the same codes as Vaillant?
Many are the same, including F22 for low pressure and F28 for ignition failure, because Glow-worm is part of the same group.
- F22 (low pressure) is usually a DIY fix: top up and reset.
- F28/F29: check the gas, condensate pipe and flue, then reset once or twice.
- F61–F84 codes point to faulty parts: call a Gas Safe engineer.
- A flashing egg timer is usually a normal waiting period, not a fault.
