What the A03 code means
Modern Vokera boilers are room sealed, which means they draw air in and push waste gases out through the flue using a fan. The fan has a small sensor called a tacho that sends a speed signal back to the control board. The board uses that signal to check the fan is running at the speed it asked for before and during ignition.
In Vokera user manuals for models such as the Vision and Vision S, A03 is listed as a fan tacho signal fault, and newer code lists describe it simply as a fan fault. If the signal is missing or wrong, the boiler locks out, because burning gas without proof that the fan is clearing the flue would not be safe. The manual's action is to reset and check the appliance operation, and to check the fan.
You may see A03 described online as an overheat or pressure code. On the Vokera manuals we checked, it is the fan fault and low pressure is A04. Older and specialist models can differ, so check the table in your own manual.
Common causes of A03
A worn or failed fan
The fan runs every time the boiler fires. Over the years its bearings can wear, and it may slow down or stop. A fan on its way out often becomes noisy first, with a whine, hum or rattle when the boiler starts.
Faulty tacho signal or wiring
Sometimes the fan spins normally but the speed signal does not reach the board. A loose plug, damaged wire or failed sensor inside the fan can cause this. Faults of this type often come and go.
Control board fault
The board powers the fan and reads its signal. If the fan and wiring test correctly, the board may be the problem.
Power supply problems
A dip in the mains supply or a power cut while the boiler is starting can interrupt the fan and trigger A03. This usually clears with a single reset.
Flue or air intake restriction
A blocked or damaged flue can make the fan struggle. This is uncommon, and checking it is strictly an engineer job. If you notice anything obviously wrong with the flue outside, such as damage or a bird nest, mention it when you book rather than trying to deal with it yourself.
| Cause | Typical sign | Who fixes it |
|---|---|---|
| Power dip or cut | A03 once, clears after a reset | You, by resetting |
| Worn fan bearings | Whining or rattling on start-up | Gas Safe engineer |
| Tacho sensor or wiring fault | A03 comes and goes, fan sounds normal | Gas Safe engineer |
| Control board fault | Fan and wiring test correctly | Gas Safe engineer |
| Flue restriction | Fault under load or in strong wind | Gas Safe engineer |
Safe checks you can do yourself
There is no homeowner fix for a fan fault, but these checks may clear a one-off lockout and will help the engineer.
- Check the power. Make sure the fused spur for the boiler is switched on and that nothing else in the house has lost power.
- Reset the boiler once using the method in your manual. On many models you hold the reset button for a few seconds, and on some you turn the selector dial to the reset position.
- Listen while the boiler starts. Note any whining, grinding or rattling from inside the casing.
- Give it several minutes to run through ignition before deciding whether the reset worked.
- Stop after two or three attempts. Repeated resets will not fix a failing fan.
Do not remove the boiler casing or try to reach the fan. It sits in the sealed combustion section, and any work there, including on the flue, must be done by a Gas Safe registered engineer.
When to call a Gas Safe engineer
If A03 comes back after two or three resets, or if the boiler has been noisy for a while, call a Gas Safe registered engineer. They will check the fan's supply and speed signal, the wiring between the fan and the board, and the flue. They may also run a combustion check once the fault is fixed.
When you book, give the exact code, the model name on the front of the boiler and a description of any noise. Many engineers carry common Vokera parts, so good information improves the chance of a one-visit fix. If your boiler is still under warranty, contact Vokera or your installer first.
Typical repair costs in the UK
If a reset clears the fault for good, there is nothing to pay. If a part is needed, these typical ranges include parts and labour.
| Job | Typical UK cost |
|---|---|
| Engineer call-out and diagnosis | Typically £80 to £150 |
| Repairing fan wiring or a connector | Typically £80 to £150 |
| Fan replacement, fitted | Typically £180 to £350 |
| Replacement PCB | Typically £300 to £550 |
| Flue repair or adjustment | Typically £100 to £300 |
How to stop A03 coming back
Fans wear gradually, so a yearly service is the best defence. The engineer checks combustion readings and listens to the fan, and can often spot wear before it becomes a breakdown. Our boiler service cost guide explains what is included. Do not ignore a boiler that has started to whine or rattle when it fires up. If your boiler also struggles to light, read our page on the Vokera A01 ignition failure, and see the Vokera fault code hub for the other codes we cover.