Vokera E077 Fault Code: Causes, Fixes & Repair Costs
What does the Vokera E077 fault code mean?
The E077 code on a Vokera boiler indicates that the control system has detected a fault within the main zone water thermostat circuit. In plain terms, the boiler's electronics are either receiving an abnormal signal — or no signal at all — from the sensor responsible for monitoring the temperature of the heating zone water. When this happens, the boiler locks out as a safety precaution, since running without reliable temperature data could lead to overheating. The fault appears on models including the Vokera Vision Plus series and related E-series ranges. Because the root cause can range from a simple wiring issue to a failed thermistor or PCB fault, a Gas Safe engineer will typically need to diagnose and resolve it.
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
- Faulty or failed zone thermistor Common
The zone thermistor is a small temperature-sensing component that feeds live water temperature data to the boiler's PCB. Over time these sensors degrade, develop an open or short circuit, and begin sending readings that fall outside expected parameters — triggering the E077 lockout. This is the single most common root cause of this fault code.
- Loose or damaged wiring connections Common
Vibration, heat cycling, and general age can cause the wiring connectors between the thermistor and the PCB to work loose or corrode. A poor connection produces erratic or absent signals that the boiler interprets as a thermostat fault, even if the sensor itself is perfectly healthy.
- Limescale or sludge around the thermistor Sometimes
In hard-water areas or systems with heavy sludge contamination, deposits can accumulate on or around the thermistor pocket. This effectively insulates the sensor from the water it is meant to measure, causing it to report inaccurate temperatures and eventually triggering a lockout.
- Faulty PCB Rare
If the PCB's input circuitry for the thermostat channel has developed a fault — due to a power surge, moisture ingress, or component age — it may misinterpret a perfectly good signal as an error, or fail to read it altogether. PCB faults are typically only diagnosed once the thermistor and wiring have been ruled out.
How to fix it
- Check system water pressure DIY safe
Look at the pressure gauge on the boiler front panel. It should read between 1.0 and 1.5 bar when the system is cold. If it is below 1.0 bar, top it up via the filling loop until it reaches approximately 1.2 bar, then attempt a reset. Incorrect pressure will not usually cause E077 directly, but it is a quick check worth doing first.
- Reset the boiler DIY safe
On models with a dedicated reset button (often labelled 'R'), press and hold it for around 3–5 seconds until the fault code stops flashing, then allow the boiler to restart. On models with a mode selector dial, turn the dial to the reset or OFF/RESET position, hold briefly, then return it to the heating position. Wait a few minutes to see whether the boiler fires up normally. Only attempt this up to two or three times — repeated resets without a fix can mask a developing problem.
- Inspect and test the zone thermistor Gas Safe engineer
A Gas Safe engineer will use a multimeter to measure the thermistor's resistance at a known water temperature and compare it against the manufacturer's specification. A reading that is significantly out of range, open-circuit, or short-circuit confirms the sensor has failed and needs replacing. The part itself is inexpensive (typically under £30), making this one of the most cost-effective repairs.
- Check all wiring and connector integrity Gas Safe engineer
The engineer will inspect the wiring loom running from the thermistor back to the PCB, looking for signs of chafing, corrosion, heat damage, or loose pins in the connectors. Reseating or replacing a faulty connector can resolve E077 without any component replacement at all.
- Power flush or chemical clean the system if contamination is suspected Gas Safe engineer
If the system water is visibly dark or the thermistor pocket shows significant scale deposits, the engineer may recommend a power flush or targeted chemical descale. This removes the debris affecting the sensor's accuracy and also benefits the system's overall efficiency.
- Test and replace the PCB if all other components check out Gas Safe engineer
Should the thermistor, wiring, and system condition all prove satisfactory, the engineer will assess the PCB. Some PCB faults are repairable (e.g. a corroded connector or failed relay), but a fully failed board will need replacement. This is the most expensive outcome and is worth weighing against the boiler's age and overall condition.
- Call a Gas Safe registered engineer if the fault persists after a reset Gas Safe engineer
If the E077 code returns after one or two resets, or if you are not comfortable carrying out even the basic pressure and reset checks, contact a Gas Safe registered engineer. Do not continue resetting in the hope the fault clears — persistent lockouts indicate a component issue that requires proper diagnosis.
Parts you may need
- Zone thermistor / temperature sensor · from £25
- Wiring harness / connector loom · 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
Can I fix the Vokera E077 fault myself?
The only safe DIY steps are checking your system pressure, topping it up if it is below 1 bar, and resetting the boiler once or twice. The actual fault — whether it is a failed thermistor, damaged wiring, or a PCB issue — involves internal electrical components that must be worked on by a Gas Safe registered engineer. Attempting to access or replace sensors yourself could void any remaining warranty and may be unsafe.
How much does it cost to fix a Vokera E077 fault in the UK?
For the most common repair — replacing the zone thermistor and labour — you can typically expect to pay between £120 and £250 including call-out, parts, and VAT. If the fault turns out to be a wiring issue, costs are often at the lower end of that range. A PCB replacement is significantly more expensive and can reach £400–£500 once parts and labour are included; if your boiler is over 10 years old, it is worth comparing that cost against a new boiler quote.
Why does my Vokera keep showing E077 after I reset it?
If E077 returns every time you reset, the underlying component fault has not been resolved. A one-off lockout can sometimes be a transient glitch, but a recurring code almost always points to a failed thermistor, a loose or corroded wiring connection, or — less commonly — a PCB fault. Each reset is simply clearing the error flag without addressing the cause, so a Gas Safe engineer needs to diagnose and fix the root problem.
Is E077 dangerous — should I turn my boiler off?
The boiler will have locked itself out automatically, so it is already in a safe state. E077 is a control-circuit fault rather than a gas or combustion safety issue, so there is no immediate danger. You do not need to isolate the gas supply unless the engineer advises it. That said, do not keep force-resetting the boiler repeatedly — if it is locking out consistently, leave it off and arrange for an engineer visit.