Vokera A06 Fault Code: DHW Thermistor Fault Explained
The A06 code indicates that your Vokera boiler has detected a problem with the DHW (domestic hot water) thermistor — the sensor responsible for measuring the temperature of your hot water. Thermistors work by producing a resistance reading (in ohms) that the boiler's PCB converts into a temperature value. When that reading falls outside acceptable limits, disappears entirely, or sits at an implausible level, the PCB flags the A06 fault and may shut the boiler down to prevent uncontrolled water temperature. The practical result is that the boiler cannot regulate hot water output reliably, leaving you with intermittent or no hot water.
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 A06 fault code mean?
The A06 code indicates that your Vokera boiler has detected a problem with the DHW (domestic hot water) thermistor — the sensor responsible for measuring the temperature of your hot water. Thermistors work by producing a resistance reading (in ohms) that the boiler's PCB converts into a temperature value. When that reading falls outside acceptable limits, disappears entirely, or sits at an implausible level, the PCB flags the A06 fault and may shut the boiler down to prevent uncontrolled water temperature. The practical result is that the boiler cannot regulate hot water output reliably, leaving you with intermittent or no hot water.
Common causes
- Faulty DHW thermistor Common
The sensor itself has degraded or failed outright. Over time thermistors drift out of calibration or develop internal faults, producing readings the PCB cannot interpret as a valid temperature. This is the single most common reason the A06 code appears and is usually the first component an engineer will test.
- Loose or damaged wiring connections Common
Boilers vibrate continuously during operation, and over months or years those vibrations can work plug-in connectors and spade terminals loose. A poor connection between the thermistor and the wiring loom mimics a faulty sensor perfectly, so the PCB sees an open circuit or erratic signal and raises the fault. Older boilers or those that have not been serviced regularly are especially prone to this.
- Faulty PCB Sometimes
The PCB is responsible for interpreting the resistance signal from the thermistor. If the relevant input circuit on the PCB has failed, it may report A06 even when the sensor and wiring are perfectly sound. An engineer will rule out the thermistor and wiring first before suspecting the PCB, as PCB replacement is considerably more involved and expensive.
How to fix it
- Try a single boiler reset DIY safe
Press and hold the reset button (or follow your model's reset procedure as described in the user handbook) for the time specified — usually around three seconds. If the boiler restarts and runs normally, monitor it closely. A one-off reset is reasonable, but if the A06 code returns within a short time, a physical fault is present and further resets will not resolve it. Do not reset more than two or three times in total.
- Check that your gas supply is live DIY safe
Confirm that other gas appliances in your home — such as a hob or gas fire — are working normally. If they are not, contact your gas supplier rather than continuing to reset the boiler. If they are working, the gas supply to the boiler is unlikely to be the problem.
- Have a Gas Safe engineer inspect the thermistor wiring and connections Gas Safe engineer
An engineer will isolate the boiler electrically, then check the wiring loom and connector at the DHW thermistor for corrosion, loose pins, or damaged insulation. A poor connection can often be repaired quickly and cheaply, avoiding the need for any parts at all.
- Test the DHW thermistor with a multimeter Gas Safe engineer
Using a multimeter set to resistance, the engineer will measure the ohm value produced by the thermistor at a known water temperature and compare it against the manufacturer's reference chart. A reading outside the expected range confirms the sensor has failed and needs replacing.
- Replace the DHW thermistor if confirmed faulty Gas Safe engineer
DHW thermistors for Vokera boilers are relatively inexpensive (typically around £20 for the part). The engineer will fit a like-for-like replacement, reconnect the wiring, and run the boiler through a hot water cycle to verify the fault has cleared and the temperature readings are stable.
- Test the PCB if the fault persists after sensor replacement Gas Safe engineer
If a new thermistor and secure wiring do not clear the A06 code, the engineer will use a multimeter to check the PCB's input circuit for the DHW sensor signal. A PCB fault is less common but possible; the engineer will advise whether replacement is cost-effective relative to the age and overall condition of the boiler.
- Contact a Gas Safe registered engineer Gas Safe engineer
All diagnostic and repair work on a Vokera boiler must be carried out by a Gas Safe registered engineer. You can find one at gassaferegister.co.uk. Ask them to check their Gas Safe ID card before any work begins.
Parts you may need
- DHW thermistor (NTC sensor) · from £20
- Thermistor wiring loom / harness · from £35
- PCB (printed circuit board) · from £180
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 £80–£250, depending on the underlying cause.
Frequently asked questions
Can I fix the Vokera A06 fault myself?
No. While you can safely attempt a boiler reset and check that your gas supply is live, all diagnostic and repair work — testing the thermistor, inspecting wiring, or replacing any component — must be carried out by a Gas Safe registered engineer. Working on a boiler's internal components without Gas Safe registration is illegal and dangerous.
How much does it cost to fix a Vokera A06 fault?
If the DHW thermistor itself is the culprit, the total repair cost — part plus labour — typically comes to somewhere between £80 and £150. If the fault turns out to be a wiring connection issue, it may be cheaper still. A PCB replacement is a less common outcome but significantly more expensive; parts alone can exceed £180, and with labour the total can push well past £300. For older boilers, an engineer may advise that a replacement boiler is more cost-effective than a PCB repair.
Will my Vokera boiler still heat my home if it shows A06?
It depends on how the boiler responds to the fault. In many cases the boiler will continue to provide central heating but lock out the domestic hot water circuit, since the A06 fault relates specifically to the DHW thermistor. In other cases the boiler may shut down completely. Either way, the fault should be investigated promptly to avoid further damage.
Could regular servicing have prevented the A06 fault?
Quite possibly, yes. An annual service by a Gas Safe engineer includes checking electrical connections and testing sensors, which means a deteriorating thermistor or a loosening connector is likely to be spotted and corrected before it triggers a fault code. Regular servicing also tends to extend the overall lifespan of the boiler.