Flue sensor damaged
The E23 error code on Ravenheat boilers indicates flue sensor damaged.
Ravenheat E23 means: flue sensor damaged. The usual causes are e23-712 main switch 4 0012pot05010/0 e23-729 d.h.w, potentiometer 5 0007ter08010/0 overheat thermostat 6 0001cam06005/0 e23-732 combustion chamber 7 0001dia06005/0 e23-730 flue restriction ring 79csi ( or e23-712 switch 3 0011gru06005/0 flow return 4 0012pot05010/0 e23-729 d.h.w. A Gas Safe registered engineer should diagnose the root cause.
What Does E23 Mean
The E23 code is shown by the boiler’s control board when it detects flue sensor damaged. The boiler then stops instead of continuing to run in that condition: the code is the appliance reporting a problem, not proof that the boiler is broken.
| What you see on the boiler |
|---|
| The display shows E23 and the boiler stops until the fault is cleared |
Common Causes
Causes documented in 2 technical sources.
| Cause |
|---|
| E23-712 Main switch 4 0012POT05010/0 E23-729 D.H.W. |
| Potentiometer 5 0007TER08010/0 Overheat thermostat 6 0001CAM06005/0 E23-732 Combustion chamber 7 0001DIA06005/0 E23-730 Flue restriction ring 79CSI ( |
| E23-712 Switch 3 0011GRU06005/0 Flow return 4 0012POT05010/0 E23-729 D.H.W. |
| Potentiometer 5 0007TER08010/0 Overheat thermostat 6 000 |
Safety Warning
E23 is a gas-related fault. Never attempt to repair or adjust the gas valve, burner assembly, or flue system yourself. All gas work must be carried out by a Gas Safe registered engineer (UK) or licensed HVAC technician (US). Repeated resets after ignition failure can cause unburnt gas to accumulate inside the combustion chamber — this is a serious safety hazard. If you smell gas at any point, turn off the gas supply at the meter, open windows, leave the property, and call your gas emergency service immediately. Gas-related fault. Do not open the boiler casing or attempt repairs to the gas valve, burner, ignition or flue. Repeated resets are unsafe. Diagnosis and repair must be carried out by a Gas Safe registered engineer.
Parts & Prices
Prices shown are indicative. Actual prices and availability vary by region.
Step-by-Step Diagnosis
Visually inspect the flue terminal outside — check for blockages, birds' nests, or ice
Check the flue run — verify it is within the manufacturer's maximum length and number of bends
Perform a flue gas analysis — CO and CO2 levels should be within specification
Check the condensate drain — ensure it is not blocked
Verify the air intake is not obstructed (for room-sealed appliances)
Check for signs of flue gas spillage in the room (for open-flue appliances)
How to Fix It
Clear any flue blockage
correct the flue installation if it exceeds maximum length or bends
clear ice from the flue terminal (insulate external condensate pipe)
clear the condensate drain
if combustion analysis shows incorrect values, adjust the gas valve or service the burner
Refer to the Ravenheat service documentation for the detailed procedure. Only a qualified engineer should carry out these repairs.
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Affected Models
Ravenheat models that can display fault code E23:
| Model Family | Output Range | Frequency |
|---|---|---|
| All Ravenheat models | — | Possible |
Frequently Asked Questions
Clear any flue blockage. According to the technical documentation, this is the first check on the list for E23.
E23 is classified as a high-severity fault: it involves gas, combustion or flue components. Do not keep resetting the boiler and do not attempt the repair yourself — call a Gas Safe registered engineer.