Ravenheat E06 Fault Code: Causes, Fixes & Repair Costs
What does the Ravenheat E06 fault code mean?
The E06 code on a Ravenheat boiler indicates that the central heating flow temperature sensor has detected an excessively high reading, causing the boiler to lock itself out as a safety measure. The sensor responsible is an NTC (Negative Temperature Coefficient) thermistor — a small heat-sensitive resistor mounted on the pipework that continuously reports water temperature to the PCB. When that reading climbs beyond safe limits, the boiler shuts down to protect itself and your home. The lockout will persist until the underlying cause is resolved; repeated resets without fixing the root problem will not clear it permanently.
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
- Limescale build-up around the thermistor Common
In hard water areas, limescale deposits can accumulate directly on or around the NTC thermistor. These deposits act as insulators that trap heat locally, so the sensor registers a temperature far higher than the actual bulk water temperature. The boiler interprets this as overheating and shuts down — even though the system as a whole may not be genuinely too hot. This is one of the most frequent triggers for E06, particularly in older systems that have never been flushed.
- Poor water circulation due to sludge or a weak pump Common
If the central heating pump is struggling, or if sludge and debris have partially blocked the system, water movement slows down. Heat then builds up locally around the sensor rather than being carried away efficiently, producing falsely elevated readings. You may also notice cold spots on radiators or a boiler that cuts out before the heating reaches temperature.
- Damaged or loose wiring to the thermistor Sometimes
The wiring that connects the NTC thermistor to the PCB can fray, chafe against sharp metal edges, or develop loose connections over time. This produces erratic or out-of-range resistance signals that the PCB interprets as dangerously high temperatures. The fault may appear intermittently at first before becoming a persistent lockout.
- Faulty or drifted thermistor sensor Sometimes
After years of service — especially in systems with a history of limescale or overheating — the thermistor itself can drift out of calibration or fail outright. A degraded sensor will report inaccurate resistance values regardless of the actual water temperature, triggering E06 even when the system is operating normally.
- Genuine system overheating Rare
In less common cases, the boiler really is overheating — typically because another safety component such as the overheat thermostat or a zone valve has failed, causing heat to build uncontrolled. The E06 lockout is then working exactly as intended to prevent damage.
How to fix it
- Reset the boiler once or twice DIY safe
Press the boiler's reset button or cycle the on/off switch as described in your user manual. If the fault clears and the boiler runs normally, monitor it over the next hour. If E06 returns quickly or repeatedly, a reset alone will not fix the problem and you should move on to the steps below rather than continuing to reset.
- Check your home's gas supply DIY safe
Make sure other gas appliances (hob, gas fire) are working normally. If there is no gas supply to the property, contact your gas supplier rather than an engineer.
- Check and top up system pressure if needed DIY safe
Look at the pressure gauge on the boiler — it should read between 1.0 and 1.5 bar when cold. If it is below 1 bar, use the filling loop to top it up following the instructions in your boiler manual. Low pressure alone rarely causes E06, but it can contribute to poor circulation that worsens the fault.
- Have a Gas Safe engineer inspect the thermistor and its wiring Gas Safe engineer
A qualified engineer will use a multimeter to measure the thermistor's resistance across a range of temperatures and compare the readings against the manufacturer's specification curve. They will also check the wiring loom for signs of chafing, corrosion, or loose terminals. This inspection pinpoints whether the sensor itself, the wiring, or a genuine overheating condition is at fault.
- Power flush the system to remove limescale and sludge Gas Safe engineer
If limescale or sludge is identified as a contributing factor, a professional power flush will clear debris from the pipework, heat exchanger, and radiators. This restores proper water flow, reduces the risk of localised hot spots around the thermistor, and extends the life of the pump and heat exchanger. A magnetic filter fitted after the flush helps prevent sludge from returning.
- Replace the NTC thermistor if it tests as faulty Gas Safe engineer
If the resistance readings are outside acceptable limits, the engineer will fit a new compatible NTC thermistor. The part itself is inexpensive (typically £15–£25), so the majority of the cost is labour. The engineer should re-test the boiler through a full heating cycle after replacement to confirm the fault is resolved.
- Dose the system with a quality inhibitor Gas Safe engineer
Once any flush or repair is complete, ask the engineer to add a corrosion and scale inhibitor such as Fernox F1 or Sentinel X100 to the system water. In hard water areas this is especially important — it slows future limescale formation around the thermistor and throughout the system. The inhibitor should be checked and topped up at each annual service.
Parts you may need
- NTC thermistor (flow or return sensor) · from £20
- Thermistor wiring harness · from £18
- Central heating pump · from £65
- Magnetic system filter (e.g. Magnaclean) · from £55
- System inhibitor (e.g. Fernox F1, 1 litre) · from £15
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–£320, depending on the underlying cause.
Frequently asked questions
Can I just keep resetting the boiler to clear E06?
Resetting may temporarily restore operation, but it does not fix the underlying cause. If the fault is being triggered by limescale on the thermistor, poor circulation, or a failing sensor, it will return — often more quickly each time. Repeated lockouts can put additional stress on other components, so it is worth having an engineer diagnose the root cause rather than relying on resets.
How much does it cost to fix a Ravenheat E06 fault in the UK?
For the most common repair — thermistor replacement, including a call-out and labour — expect to pay roughly £100–£200. If the system also needs a power flush to clear limescale or sludge, that typically adds £300–£500 on top. In rare cases where the PCB or gas valve is involved, costs can rise significantly and it may be worth considering a full boiler replacement, particularly if your Ravenheat is more than 10 years old.
What is an NTC thermistor and why does it cause E06?
An NTC (Negative Temperature Coefficient) thermistor is a small resistor whose electrical resistance drops as temperature rises. The boiler's PCB uses this changing resistance to calculate water temperature in real time. When the thermistor is coated in limescale, damaged, or simply worn out, it sends resistance readings that correspond to dangerously high temperatures — even if the water is actually fine. The PCB responds by locking the boiler out, which is what produces the E06 code.
Will a power flush definitely fix E06 on my Ravenheat boiler?
A power flush is the right first step if limescale or sludge is confirmed as the cause, and it often resolves or reduces the frequency of E06. However, if the thermistor itself has been permanently damaged by heat or limescale exposure, it will need replacing even after the flush. A Gas Safe engineer can test the sensor's resistance to determine whether flushing alone is sufficient or whether a new thermistor is also required.