Ravenheat CSI 85 Fault codes & diagnostics

21 fault codes with plain-English explanations, severity ratings, DIY guidance, and repair cost estimates.

Combi Natural Gas 24.9 kW Discontinued

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Severity at a glance

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19 High 1 Medium 1 Low
Just want the most common Ravenheat CSI 85 faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 21 documented codes

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E02

Your boiler has stopped working because water is not moving through the system properly, which is causing it to overheat and shut down for safety.

High DIY-safe £180-350

What to check first

  1. Check that your system pressure is between 1.0 and 1.5 bar on the pressure gauge
  2. Ensure all radiator valves and isolation valves under the boiler are fully open
  3. Bleed your radiators to remove any trapped air that might be blocking circulation
  4. Press the reset button to see if the boiler restarts

Parts commonly replaced

  • Circulating pump
  • Automatic air vent
  • Main heat exchanger (de-scaling)

Related codes

Full explanation for E02
E03

Your boiler has detected an issue with the sensor that monitors water movement, preventing the system from heating up properly.

High Engineer only £125-£210

Parts commonly replaced

  • Flow sensor
  • NTC thermistor
  • Wiring harness

Related codes

Full explanation for E03
E04

Your boiler has detected a problem with the sensor that monitors hot water temperature, meaning you will likely have no hot water or inconsistent temperatures.

Medium Engineer only £90-160

Parts commonly replaced

  • DHW Temperature Sensor (NTC Thermistor)
  • Connecting wiring harness

Related codes

Full explanation for E04
E05

Your boiler has detected an issue with the fan that clears exhaust gases, preventing the system from starting for safety reasons.

High Engineer only £180-350

Parts commonly replaced

  • Fan assembly
  • Fan wiring harness
  • Printed Circuit Board (PCB)

Related codes

Full explanation for E05
E06

Your boiler has detected that the water temperature in your heating system is getting too high, causing it to shut down for safety.

High DIY-safe £90-180

What to check first

  1. Check that all radiator valves are fully open
  2. Ensure the boiler pressure is between 1.0 and 1.5 bar
  3. Check if any bypass valves are closed
  4. Reset the boiler to see if the fault clears

Parts commonly replaced

  • Central Heating NTC Temperature Sensor
  • Internal Circulation Pump

Related codes

Full explanation for E06
E08

Your boiler has detected that there is not enough water in the system to operate safely and has shut down to prevent damage.

High DIY-safe £0-160

What to check first

  1. Locate the filling loop (usually a silver flexible hose) underneath your boiler.
  2. Slowly open the small valves at either end of the hose until you hear water entering the system.
  3. Monitor the pressure gauge and close the valves once the needle reaches between 1.0 and 1.5 bar.
  4. Reset the boiler to clear the fault code.

Parts commonly replaced

  • Filling loop
  • Expansion vessel
  • Pressure relief valve

Related codes

Full explanation for E08
E09

Your boiler has shut down because it has detected its internal temperature is getting too hot, usually caused by a blockage or a pump failure.

High DIY-safe £120-350

What to check first

  1. Check that your radiator valves are fully open to allow water to flow.
  2. Check that your system pressure is between 1 and 1.5 bar on the gauge.
  3. Try resetting the boiler to see if the fault clears after the system has cooled down.

Parts commonly replaced

  • Circulation pump
  • Overheat thermostat
  • Main heat exchanger

Related codes

Full explanation for E09
E10

Your boiler has too much water in the system, which puts extra stress on the internal components.

Low DIY-safe £80-160

What to check first

  1. Check that the filling loop valves are fully closed
  2. Bleed water from a radiator using a bleed key to reduce pressure
  3. Monitor the pressure gauge until it returns to between 1 and 1.5 bar
  4. Rest the boiler if the code persists

Parts commonly replaced

  • Filling loop valve
  • Expansion vessel
  • Pressure relief valve

Related codes

Full explanation for E10
E13

Your boiler's internal computer has encountered a glitch or a configuration error and cannot communicate properly with the system.

High DIY-safe £220-450

What to check first

  1. Locate the reset button or dial on the boiler control panel
  2. Press and hold the reset button for 5 seconds, then release
  3. Wait 2 minutes for the boiler to restart; if the code persists, a professional must inspect the electronics

Parts commonly replaced

  • Printed Circuit Board (PCB)
  • Main Control Board
Full explanation for E13
E21

Your boiler has detected that the water returning from your radiators is too hot, causing the system to shut down to prevent damage.

High DIY-safe £120-250

What to check first

  1. Check that all radiator valves are fully open
  2. Ensure the central heating system pressure is between 1.0 and 1.5 bar
  3. Switch the boiler off and on again to see if the fault clears after the system cools down

Parts commonly replaced

  • CH Return NTC Sensor
  • Central Heating Pump
  • Secondary Heat Exchanger

Related codes

Full explanation for E21
Showing 11–20 of 21
E22

Your boiler has sensed that the exhaust gases are becoming too hot and has shut down as a safety precaution.

High Engineer only £120-280

Parts commonly replaced

  • Flue NTC sensor
  • Main heat exchanger
  • Burner gasket

Related codes

Full explanation for E22
E23

Your boiler has detected a fault with the sensor that monitors exhaust gases, and as a safety precaution, it will not operate until this is fixed.

High Engineer only £120-£210

Parts commonly replaced

  • Flue Gas NTC Sensor
  • Connecting Wiring Harness

Related codes

Full explanation for E23
E24

Your boiler has detected a problem with the sensor that monitors the water temperature returning from your radiators, preventing the system from operating correctly.

High Engineer only £90-160

Parts commonly replaced

  • Central heating return NTC sensor
  • Wiring harness
  • Main circuit board (PCB)

Related codes

Full explanation for E24
E25

Your boiler has detected that the water inside the main heating unit has frozen due to extremely cold temperatures, preventing it from operating.

High DIY-safe £80-160

What to check first

  1. Check if any external condensate pipes are frozen and thaw them with warm (not boiling) water.
  2. Increase the room thermostat setting to encourage movement in the system.
  3. Ensure the boiler is located in a draft-free area and keep the heating on a low constant setting during cold snaps.
  4. Reset the boiler once the unit has thawed out.

Parts commonly replaced

  • Condensate pipe insulation
  • Trace heating cable
  • Main heat exchanger

Related codes

Full explanation for E25
E29

Your boiler has detected that the water used for your taps and showers is getting too hot, causing the system to shut down for safety.

High Engineer only £90-180

Parts commonly replaced

  • DHW Temperature Sensor (NTC thermistor)
  • Limescale-blocked Heat Exchanger
  • Diverter Valve

Related codes

Full explanation for E29
E31

Your boiler has lost its digital connection with your external smart thermostat or heating controls, meaning it cannot receive instructions to turn on.

High DIY-safe £70-180

What to check first

  1. Check that your external thermostat or wall control is powered on and has fresh batteries
  2. Ensure the wires connecting your thermostat to the boiler haven't been accidentally bumped or damaged
  3. Turn the boiler off at the main power switch, wait 30 seconds, and turn it back on to reset the connection

Parts commonly replaced

  • External Thermostat Unit
  • OpenTherm Interface Module
  • Control Wiring

Related codes

Full explanation for E31
E41

Your boiler has sensed an unusual temperature difference between the water leaving it and the water returning, suggesting that water is not circulating through your heating system correctly.

High DIY-safe £100-350

What to check first

  1. Check that all radiator valves (TRVs) are fully open
  2. Ensure your system pressure is topped up to roughly 1.5 bar
  3. Bleed all radiators to remove trapped air locks
  4. Restart the boiler using the reset button

Parts commonly replaced

  • Circulation Pump
  • Flow/Return NTC Sensors
  • Main Heat Exchanger (if blocked)

Related codes

Full explanation for E41
E42

Your boiler has detected that heat is not moving through the system correctly, usually meaning the water is hotter in one part of the machine than another.

High Engineer only £120-£350

Parts commonly replaced

  • Temperature sensors (NTC thermistors)
  • Circulation pump
  • Heat exchanger

Related codes

Full explanation for E42
E43

Your boiler has detected an unusual temperature difference between internal parts, suggesting that water is not circulating correctly through the system.

High DIY-safe £120-£350

What to check first

  1. Check that your system pressure is between 1.0 and 1.5 bar
  2. Ensure all radiator valves and isolation valves are fully open
  3. Try resetting the boiler to clear the temporary sensor glitch

Parts commonly replaced

  • Circulation Pump
  • Temperature Sensors (NTC Thermistors)
  • Main Heat Exchanger

Related codes

Full explanation for E43
E44

Your boiler has detected an unusual temperature difference between internal sensors, suggesting a possible circulation issue or a faulty component.

High Engineer only £120-280

Parts commonly replaced

  • NTC Temperature Sensor
  • Circulation Pump
  • Printed Circuit Board (PCB)

Related codes

Full explanation for E44
Showing 21–21 of 21
E46

Your boiler is having trouble monitoring its internal water pressure, which has caused it to stop working for safety.

High Engineer only £120-210

Parts commonly replaced

  • Water pressure sensor
  • Wiring harness
  • Main circuit board (PCB)

Related codes

Full explanation for E46