Vokera A03 Fault Code: Fan Tacho Signal Fault
The A03 code appears when the boiler's printed circuit board (PCB) detects a problem with the fan's tacho signal — essentially, the feedback the PCB uses to confirm the fan is spinning at the correct speed. Without a valid signal, the boiler cannot verify that exhaust gases are being safely expelled through the flue, so it locks out as a precaution. This fault is particularly prevalent on the Vokera Compact range but can appear across several Vokera models.
General guidance only — not a substitute for professional advice. Any gas work must be carried out by a Gas Safe registered engineer. If you smell gas or suspect carbon monoxide, leave the property and call the National Gas Emergency line on 0800 111 999.
What does the Vokera A03 fault code mean?
The A03 code appears when the boiler's printed circuit board (PCB) detects a problem with the fan's tacho signal — essentially, the feedback the PCB uses to confirm the fan is spinning at the correct speed. Without a valid signal, the boiler cannot verify that exhaust gases are being safely expelled through the flue, so it locks out as a precaution. This fault is particularly prevalent on the Vokera Compact range but can appear across several Vokera models.
Common causes
- Incorrect or drifted fan speed setting Common
Some Vokera fans ship with a speed setting that sits outside the acceptable range, or the setting drifts over time. If the fan runs too slowly, the tacho signal falls below the threshold the PCB expects and A03 is triggered. A Gas Safe engineer can measure and adjust the speed to the correct value.
- Worn fan bearings Common
Continuous operation causes the fan's internal bearings to wear down, resulting in an inconsistent or erratic tacho signal even when the fan appears to be turning. You may hear a grinding or rattling noise from the boiler before the lockout. Bearing replacement kits are available, but the engineer should also assess the fan's overall condition while the boiler is open.
- Loose or damaged wiring at the fan Common
Vibration over time can loosen the electrical connections between the fan and the PCB, interrupting the tacho signal intermittently. A power surge can also damage the wiring insulation. This is often an inexpensive fix once the faulty connection is located.
- Blocked flue or air intake Sometimes
A nest, debris, or external obstruction restricting airflow through the flue or air intake can prevent the fan from reaching its target speed, causing the PCB to log a tacho fault. Checking for visible external blockages is one of the few homeowner-safe checks for this code.
- Moisture ingress from an internal leak Sometimes
A slow internal leak — from a heat exchanger, pump seal, or pipe joint — can allow condensation or water to settle on the fan motor or its wiring. Older Vokera units in particular may have less well-sealed electrical enclosures, making moisture damage more likely. The underlying leak must be fixed alongside the fan repair, or the fault will return.
- Faulty PCB Rare
Because the PCB is responsible for interpreting the tacho signal, a failing PCB can misread or ignore a perfectly healthy fan. This is a less common cause, but it should be considered — and ruled out with multimeter testing — before an expensive PCB replacement is authorised.
How to fix it
- Check for obvious external flue or air-intake obstructions DIY safe
Go outside and look at where the flue terminal exits the wall or roof. Remove any visible debris such as leaves, cobwebs, or bird-nesting material that is partially blocking the outlet or inlet. Do not attempt to dismantle any flue components.
- Listen to the boiler at start-up DIY safe
Before resetting, switch the boiler to heating mode and listen carefully near the casing. A complete absence of fan noise may indicate no power is reaching the motor; grinding, rattling, or a slow spin-up suggests mechanical wear or bearing damage. Note what you hear — it is useful information for the engineer.
- Reset the boiler (once or twice only) DIY safe
Locate the reset button on the boiler's control panel and hold it for the duration specified in your user guide (typically 3–5 seconds). Allow the boiler to attempt a full start cycle. If it locks out again immediately, do not keep resetting — repeated resets on a fan fault will not resolve the underlying problem and may mask diagnostic information for the engineer.
- Engineer inspection: fan wiring and connections Gas Safe engineer
A Gas Safe engineer will isolate the boiler electrically and visually inspect all wiring and plug connections at the fan. Loose terminals are re-secured or replaced, and the wiring loom is checked for heat damage or corrosion. This is often the quickest and least costly repair.
- Engineer check: fan speed measurement and adjustment Gas Safe engineer
Using appropriate diagnostic tools, the engineer measures the fan's actual operating speed and compares it against the manufacturer's specification for the specific model. If the speed is out of range, they will adjust the setting and retest, including verifying that the air pressure switch responds correctly at the new speed.
- Engineer check: fan motor and bearing assessment Gas Safe engineer
The engineer will spin the fan manually (with the boiler isolated) to feel for roughness or stiffness that indicates bearing wear. If bearings are the only issue, a repair kit may be fitted; if the motor itself is damaged or heavily worn, a full fan unit replacement is the more reliable long-term solution.
- Engineer check: inspect for internal water leaks Gas Safe engineer
If any moisture or corrosion is found on the fan or its wiring, the engineer must trace and fix the source — whether that is a weeping heat exchanger, a pump seal, or a pipework joint. Replacing the fan without addressing a leak means the fault is likely to return within months.
- Engineer check: PCB diagnostic Gas Safe engineer
Only after the fan, wiring, and any leaks have been investigated and cleared should the PCB be considered. The engineer uses a multimeter to verify that the PCB is correctly sending power to the fan and receiving the tacho signal in return. PCB replacement is a last resort and should be confirmed by testing, not assumed.
- Call a Gas Safe registered engineer if the fault persists or you are unsure Gas Safe engineer
The A03 code involves the flue and exhaust system, which are safety-critical. If your reset attempts have not cleared the fault, or if you are hearing unusual noises, do not continue using the boiler. Contact a Gas Safe registered engineer to carry out a full diagnosis.
Parts you may need
- Vokera fan motor / fan assembly · from £90
- Fan bearing repair kit · from £20
- Fan wiring loom / harness · from £35
- Air pressure switch · from £40
- PCB (printed circuit board) · from £220
The exact spare depends on your boiler's GC number (on the data badge). Check this against the part before buying.
Typical repair cost
Expect to pay roughly £120–£320, depending on the underlying cause.
Frequently asked questions
Is the Vokera A03 fault dangerous?
Yes, it warrants prompt attention. The fan is responsible for pushing combustion gases — including carbon monoxide — safely out through the flue. If the fan is not working correctly, those gases could potentially remain inside the appliance or, in a worst case, enter your home. The boiler locks itself out precisely to prevent this risk, so do not attempt to bypass the lockout or repeatedly reset without investigating the cause.
Can I fix the Vokera A03 fault myself?
Homeowners can safely check for external flue blockages and attempt one or two resets. Beyond that, the work involves electrical components inside the boiler and the flue system, both of which require a Gas Safe registered engineer. Attempting DIY repairs on the fan, wiring, or PCB is unsafe and could also invalidate your boiler warranty or home insurance.
How much does it cost to fix a Vokera A03 fault in the UK?
Most people with this fault pay somewhere between £120 and £320, depending on whether the fix is a wiring repair at the lower end or a full fan unit replacement at the higher end. If the PCB turns out to be the root cause, a replacement board can cost £300–£500 for parts alone, plus labour — though engineers should confirm this with multimeter testing before proceeding, as PCB mis-diagnoses do happen.
My Vokera boiler keeps showing A03 after resetting — what should I do?
If the fault returns immediately or within a short time of resetting, it is a sign that the underlying problem has not been resolved. Continuing to reset a boiler with a persistent fan fault is not a solution and delays a proper repair. Book a Gas Safe engineer to carry out a thorough inspection of the fan, its wiring, and the flue system. The sooner it is diagnosed, the less likely the fault is to cause further damage to other components.
Should I repair or replace my Vokera boiler if I get an A03 fault?
If the boiler is under seven years old and only the fan needs attention, repair is almost always the right call. If the boiler is older and the engineer finds additional worn components alongside the fan, or if the PCB also needs replacing, get a quote for a new boiler before committing to a large repair bill. As a rough guide, if the repair cost exceeds half the price of a comparable new boiler, replacement usually offers better long-term value — particularly as a new boiler will come with a manufacturer warranty.