Ravenheat E09 Fault Code: Causes, Fixes & Repair Costs
What does the Ravenheat E09 fault code mean?
The E09 fault code on Ravenheat boilers indicates that the overheat thermostat (also referred to as the high-limit sensor) has registered an excessively high temperature and triggered a safety lockout. When this happens, the boiler shuts itself down to prevent unsafe operation, and you may notice a red warning light flashing on the control panel. The lockout can be caused by a genuine overheating event within the boiler, or by the sensor itself failing and sending a false signal to the PCB. Either way, the boiler will not resume normal operation until the underlying cause has been identified and resolved. Note: this code is sometimes displayed as 09E on certain Ravenheat control panels — both refer to the same overheat lockout condition.
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 degraded overheat thermostat Common
The overheat thermostat is a safety component that can wear out or fail outright over time, causing it to trip at temperatures lower than it should, or to send a continuous fault signal even when the boiler is not genuinely overheating. This is one of the most common triggers for E09 on older Ravenheat units.
- Limescale or sludge contamination Common
Deposits of limescale or central heating sludge can coat the sensor or accumulate around the heat exchanger, creating localised hot spots. Much like the kettling effect in a scaled heat exchanger, these hot spots cause the sensor to read a much higher temperature than the bulk water temperature, tripping the overheat lockout prematurely.
- Poor water circulation Sometimes
A failing or seized pump, a partially blocked filter, or a heavily sludged system can prevent water from flowing through the heat exchanger fast enough to carry heat away. The resulting localised overheating is real — not a sensor error — and will continue triggering E09 until circulation is restored.
- Wiring or NTC thermistor fault Sometimes
Damaged, corroded, or loose wiring to the NTC thermistors (temperature sensors monitoring flow and return temperatures) can produce erratic or spuriously high temperature readings at the PCB, causing it to trigger the overheat lockout as a precaution.
- PCB fault Rare
In rarer cases the PCB itself misinterprets sensor signals or develops a fault that causes it to register an overheat condition incorrectly. This is more likely if the boiler has had repeated E09 lockouts over a long period.
How to fix it
- Check the boiler's gas supply DIY safe
Make sure the gas isolation valve on the supply pipe to the boiler is fully open and that other gas appliances in your home are working. If there is no gas supply, contact your gas supplier rather than attempting any boiler work.
- Reset the boiler once or twice DIY safe
Press and hold the reset button (or switch the boiler off and back on using the mains switch, depending on your Ravenheat model) to attempt to clear the lockout. Wait a minute or two and observe whether the boiler fires up normally. If it locks out again immediately or within a short time, do not keep resetting — repeated resets without resolving the cause can mask a genuine safety problem.
- Check system pressure DIY safe
Look at the pressure gauge on the boiler front. Most Ravenheat boilers operate correctly between 1.0 and 1.5 bar when cold. If pressure is very low (below 0.5 bar) or very high, this can contribute to circulation and overheating issues. Topping up via the filling loop is a homeowner task, but if pressure keeps dropping, tell your engineer.
- Do not attempt to bypass or tamper with the overheat thermostat Gas Safe engineer
The overheat thermostat is a critical safety device. Removing, bridging, or adjusting it without proper qualification is dangerous and potentially illegal. Leave all testing and component work to a Gas Safe registered engineer.
- Have a Gas Safe engineer diagnose the root cause Gas Safe engineer
An engineer will test the overheat thermostat and NTC thermistors with a multimeter to determine whether they have failed or are reading correctly. They will also inspect the heat exchanger and system for sludge or limescale, check pump operation, and examine all relevant wiring and connections before recommending a repair.
- Carry out the recommended repair — sensor, pump, or system clean Gas Safe engineer
Depending on what the engineer finds, the fix may involve replacing the overheat thermostat or an NTC thermistor (relatively inexpensive), replacing or freeing a seized pump, or carrying out a power flush to clear sludge and scale. If the PCB has been damaged by repeated overheating events, it may need replacement too.
- Consider parts availability before committing to an expensive repair DIY safe
Ravenheat Manufacturing Limited was dissolved in 2025 and parts are becoming increasingly scarce. Before authorising a costly repair (particularly PCB or gas valve replacement), ask your engineer to confirm parts availability and cost. For boilers over 10 years old, a new boiler installation may be more economical in the long run.
Parts you may need
- Overheat thermostat (high-limit stat) · from £25
- NTC thermistor (flow or return sensor) · from £15
- Circulation pump · from £65
- 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 £120–£320, depending on the underlying cause.
Frequently asked questions
Can I just keep resetting my Ravenheat boiler to clear the E09 code?
Resetting once or twice is fine as a first step, but if the boiler locks out again shortly afterwards you should stop. The E09 code indicates the overheat safety circuit has tripped, and repeatedly resetting without fixing the cause means running the boiler in an unsafe condition. You need a Gas Safe engineer to find out why it keeps overheating.
Ravenheat has gone out of business — can I still get parts to fix an E09 fault?
Ravenheat Manufacturing Limited was formally dissolved in 2025, and sourcing genuine replacement parts is becoming progressively harder. For straightforward sensor or thermistor replacements, compatible generic parts may still be available through heating merchants. However, for major components such as PCBs or gas valves, you may face long lead times, second-hand parts, or no availability at all. If your boiler is more than ten years old and needs a significant repair, it is worth getting a boiler replacement quote alongside any repair estimate.
How much does it typically cost to fix a Ravenheat E09 fault?
For the most common repairs — replacing the overheat thermostat or an NTC thermistor — most homeowners pay in the region of £120 to £320 including parts, labour, and the call-out charge. A pump replacement sits towards the upper end of that range. If the PCB has been damaged it can cost £350 to £500 or more, but this is less common. Getting an itemised quote before work begins is always advisable.
What is the difference between the overheat thermostat and an NTC thermistor on a Ravenheat boiler?
The overheat thermostat (high-limit stat) is a dedicated safety device that physically cuts power to the burner circuit if the boiler body reaches a dangerously high temperature. NTC thermistors are electronic temperature sensors that monitor the flow and return water temperatures and feed readings to the PCB for normal control purposes. Either can trigger an E09 lockout — the overheat stat by tripping its safety circuit, or an NTC thermistor by sending an erroneously high temperature signal to the PCB.