Vokera E085 Fault Code: Causes, Fixes & Repair Costs
What does the Vokera E085 fault code mean?
The E085 code appears on Vokèra boilers — most commonly the Evolve range — to signal that the appliance has detected a problem with the fumes exit path, meaning exhaust gases cannot be confirmed as leaving the property safely through the flue. The boiler locks out as a precaution to prevent potentially dangerous combustion gases from accumulating. A closely related code, E090, points to a flue over-temperature probe fault where the sensor itself records abnormally high flue gas temperatures — both codes concern the same flue and exhaust pathway, so the diagnostic steps overlap significantly. Because this fault directly involves the safe venting of combustion gases, it should be treated as a priority and not repeatedly reset in the hope it will clear on its own.
General guidance only — not a substitute for professional advice, and not certified by a Gas Safe engineer. Always have your specific appliance assessed by a qualified professional. 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.
Common causes
- Blocked or obstructed flue terminal Common
The most frequent cause of E085 in UK homes is a physical blockage at the external flue outlet. Leaves, debris, bird nests, or even a build-up of ice and snow in winter can restrict the flow of exhaust gases enough to trigger the fault. A quick visual inspection of the terminal from outside — without climbing on the roof — can sometimes reveal an obvious blockage.
- Faulty or seized flue fan Common
The fan draws combustion air into the burner and pushes exhaust gases out through the flue. If it runs slowly, intermittently, or not at all, the boiler cannot confirm safe airflow and will lock out. Fan motors on Vokèra boilers can wear over time, and a faulty capacitor or seized bearing is a common cause of E085 on older appliances.
- Defective flue thermistor or over-temperature sensor Common
The boiler monitors flue gas temperature via a dedicated thermistor. If this sensor develops a fault — giving an out-of-range reading or failing entirely — the boiler interprets the reading as evidence of an unsafe condition and shuts down. This is also the primary trigger for the related E090 code. The sensor itself is a relatively inexpensive part, though fitting requires an engineer.
- Scaled or fouled primary heat exchanger Sometimes
A heat exchanger clogged with limescale or combustion deposits can cause flue gases to back up or overheat, raising flue temperatures beyond safe limits. This is more likely in hard-water areas and in boilers that have not been serviced regularly. A power flush or descale may be needed alongside clearing the fault.
- Incorrectly installed or damaged flue pipework Sometimes
Flue sections that have become disconnected, were originally installed at the wrong angle, or have developed cracks can allow exhaust gases to recirculate back into the boiler — triggering the safety lockout. This is more common after building work or if the boiler has never been properly commissioned.
- PCB fault causing false triggering Rare
In a minority of cases, the printed circuit board misinterprets signals from the fan or flue sensors and raises the E085 alarm even when the flue itself is clear. This is typically only suspected once all other components have been checked and found to be in good order.
How to fix it
- Check the external flue terminal for visible blockages DIY safe
Go outside and look at where the flue exits the wall or roof. Look for obvious obstructions such as leaves, a bird nest, debris, or snow and ice built up around the terminal. Do not climb a ladder onto the roof — only check what you can safely see from ground level. If you spot a blockage you can safely remove from ground level, do so and then attempt a reset.
- Attempt a single boiler reset DIY safe
On most Vokèra Evolve models, press and hold the reset button (marked R or with a reset symbol) for 3–5 seconds until the fault code stops flashing, then release and allow the boiler to restart. On dial-style models, turn the selector to the reset or OFF/RESET position and hold briefly. If the boiler fires up and runs normally, monitor it over the next day or two. Do not attempt more than one or two resets — if the fault returns, stop resetting and call an engineer, as continuing to reset a flue-path fault can be unsafe.
- Engineer to inspect and clear the flue system Gas Safe engineer
A Gas Safe registered engineer will carry out a thorough inspection of the entire flue run, from the boiler connection to the external terminal. They will check for blockages, confirm all sections are correctly joined and at the right angle, and clear any debris inside the flue pipework — not just at the visible terminal end.
- Engineer to test the flue fan Gas Safe engineer
The engineer will measure the fan's speed and electrical supply to determine whether it is operating within specification. If the fan motor is failing or the capacitor is degraded, replacement is usually the most reliable fix. Vokèra fan assemblies are a known wear item and replacing the unit outright is generally more dependable than attempting piecemeal repair.
- Engineer to test and replace the flue thermistor or over-temperature sensor Gas Safe engineer
Using a multimeter, the engineer will check the resistance of the flue thermistor against the values specified for the model. A reading outside the expected range confirms sensor failure. This is also the check that distinguishes a true E085 (airflow/obstruction) from an E090 (over-temperature probe) root cause. Replacement parts are inexpensive; the cost is primarily in labour.
- Engineer to inspect and clean the primary heat exchanger if required Gas Safe engineer
If scale or combustion deposits are found to be restricting flow or causing overheating, the engineer may recommend a chemical clean or power flush. In severe cases, a replacement heat exchanger may be needed, though this is uncommon when the boiler has been regularly serviced.
- If fault persists, have the PCB investigated Gas Safe engineer
Should all the above components test as healthy, the engineer may turn their attention to the PCB. Given the cost of a Vokèra PCB replacement, the engineer should advise on whether repair is economical relative to the boiler's age and overall condition before proceeding.
Parts you may need
- Vokèra flue fan assembly · from £120
- Flue thermistor / over-temperature sensor · from £22
- Flue terminal kit (horizontal) · from £45
- Primary heat exchanger (Evolve series) · 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 £100–£350, depending on the underlying cause.
Frequently asked questions
Is the Vokèra E085 fault dangerous — can I keep using the boiler?
You should not continue using the boiler while E085 is displayed. The code means the appliance cannot confirm that exhaust gases are leaving safely, which is a potential carbon monoxide risk. Switch the boiler off and arrange for a Gas Safe registered engineer to inspect it. One reset attempt is reasonable if you can first see and clear an obvious external blockage, but do not keep resetting it in the hope it will go away.
What is the difference between E085 and E090 on a Vokèra boiler?
Both codes relate to the flue and exhaust gas system. E085 signals an obstruction or problem in the fumes exit path — typically a blocked flue, a fan issue, or a sensor reading that suggests gases cannot exit safely. E090 is more specifically a flue over-temperature probe fault, where the sensor records an abnormally high temperature in the flue gases. In practice, both codes often lead an engineer to check the same components: the fan, the flue thermistor, and the flue pipework itself.
How much does it typically cost to fix a Vokèra E085 fault?
Most homeowners pay between £100 and £350 to resolve this fault. A flue clearance or thermistor swap sits at the lower end, while a full fan replacement with parts and labour usually falls in the £200–£300 range. A straightforward horizontal flue replacement adds roughly £200. If the PCB turns out to be the underlying cause, costs can rise to £400–£500 or more — at which point it is worth asking your engineer whether repair makes financial sense on an older Vokèra, or whether a new boiler installation is a better investment.
Can a Gas Safe engineer fix this on the same visit, or will parts need to be ordered?
It depends on the root cause. A blocked flue can often be cleared on the first visit with no parts needed. If the flue thermistor or fan needs replacing, many engineers carry common Vokèra parts or can source them quickly — same-day or next-day resolution is often achievable. Less common components such as a heat exchanger or PCB may need to be ordered, meaning a return visit is required.