- Boilers
- Gas boiler
CC
Junkers CC on a gas boiler: outdoor sensor not detected
Risk level
Low
Usually safe to check without specialist tools.
Urgency
Low
Quick answer
Junkers CC means the boiler does not detect the outdoor temperature sensor. From the ground, check whether the sensor on the outside wall or its cable is damaged or pulled off, without opening anything, and ask the technician to test the sensor and cable.
Safety first
Stop and check this first
- Do not climb onto roofs, high balconies or ladders to check the sensor or its cable. Look from the ground and leave the repair to the technician.
- If you smell gas: close the gas shut-off valve, open the windows, do not operate switches, put out any flame and, from outside the home, call the gas company and an authorised installer. If you smell flue gases: switch the boiler off, open doors and windows and call the installer.
Safe checks you can perform
- Whether there is an outdoor sensor
- Visible sensor cable
- Sensor and cable test by the technician
Leave these tasks to a qualified professional
- Do not attempt this professional task: Cable continuity test
- Do not attempt this professional task: Outdoor sensor reading against its table
What a technician must be able to justify
Technician visit
These are the steps they must carry out and show you. Tick them as they work: if steps are skipped, do not accept a part swap.
These are not instructions for opening or handling the equipment yourself. They are the checks that should support a technical conclusion.
Cable continuity test
What they doThe technician checks continuity of the sensor cable to its connection at the boiler.
They must show youthe continuity test.
In writingwhere the break was and how it was repaired, or the part number of the replaced sensor.
Outdoor sensor reading against its table
What they doThe technician measures the outdoor sensor's resistance with a multimeter and compares it with the manufacturer's specification for the current temperature.
They must show youthe measured value against the manufacturer's specification.
In writingthe value and the conclusion.
Before accepting a part or repair
Nothing has been shown yet. Do not accept a part swap based on the code alone.
Follow these steps
Note: Follow the documented order. An error code identifies the affected system, but it does not prove by itself which part has failed.
Whether there is an outdoor sensor
- Who:
- you.
- How:
- look on the outside walls for a small sensor box with a cable towards the boiler. Look from the ground.
- Result that matters:
- whether there is a sensor and whether it is in place.
- If you find no sensor:
- tell the technician; it may be a setup issue.
- If there is one:
- go on to check the visible cable.
- Evidence to keep:
- a photo of the sensor and where it is.
Evidence: Junkers CerapurComfort ZWBC 25-2 C, instrucciones de instalación y manejo para el técnico · Junkers ZWE 24-3 y 28-3 H A con Bosch Heatronic, instrucciones de instalación
Visible sensor cable
- Who:
- you.
- How:
- follow the cable by eye along the wall or trunking, without climbing or pulling it.
- Result that matters:
- whether the cable is cut, crushed or loose.
- If it is damaged:
- Bosch says to check the cable for breaks; show the photo to the technician.
- If it looks intact:
- the break may be in a hidden section or in the sensor itself.
- Evidence to keep:
- photos of the cable route.
Evidence: Junkers CerapurComfort ZWBC 25-2 C, instrucciones de instalación y manejo para el técnico · Junkers ZWE 24-3 y 28-3 H A con Bosch Heatronic, instrucciones de instalación
Sensor and cable test by the technician
- Who:
- authorised technician.
- How:
- measures the outdoor sensor and the cable continuity to the boiler.
- Result that matters:
- whether the circuit is open and where.
- If the cable is broken:
- that confirms the cause and it is repaired.
- If the cable is fine and the sensor does not respond:
- it points to the sensor.
- Evidence to keep:
- a report with the measured values.
Measuring at the boiler terminals means opening it and working near mains voltage: authorised technician only.
Evidence: Junkers CerapurComfort ZWBC 25-2 C, instrucciones de instalación y manejo para el técnico · Junkers ZWE 24-3 y 28-3 H A con Bosch Heatronic, instrucciones de instalación
Still not solved
If the error persists, stop here. See what the technician must do and show you.
Where this code applies
A code is meaningful only inside the right product and version context.
Primary scope
- System
- Boilers
- Brand
- Junkers
- Product type
- Gas boiler
Known code variants
- C C
- Cerapur CC
- Error CC Junkers
- Junkers C C
What it means
In the CerapurComfort table, CC means the outdoor temperature sensor is not detected; on the ZWE with the TA 211 E controller, that the outdoor sensor has an open circuit. The outdoor sensor feeds weather compensated control, which sets the flow temperature. Bosch says to check that the sensor and its connecting cable have no break. The code points to an open circuit, it does not prove the sensor is broken.
Warnings and stop conditions
- Mediumeditorial warning
Do not climb onto roofs, high balconies or ladders to check the sensor or its cable. Look from the ground and leave the repair to the technician.
Evidence: Junkers CerapurComfort ZWBC 25-2 C, instrucciones de instalación y manejo para el técnico
- Criticalsource verified
If you smell gas: close the gas shut-off valve, open the windows, do not operate switches, put out any flame and, from outside the home, call the gas company and an authorised installer. If you smell flue gases: switch the boiler off, open doors and windows and call the installer.
Evidence: Junkers Cerapur Excellence Compact, instrucciones de uso de la caldera mural a gas de condensación · Junkers ZWE 24-3 y 28-3 H A con Bosch Heatronic, instrucciones de instalación
Symptoms and causes
Probable causes · in order
- Sensor cable cut or disconnectedCommon
Bosch says to check the cable for breaks. It fits if there has been building work, pruning or damage to the wall the cable runs along.
Evidence: Junkers CerapurComfort ZWBC 25-2 C, instrucciones de instalación y manejo para el técnico · Junkers ZWE 24-3 y 28-3 H A con Bosch Heatronic, instrucciones de instalación
- Faulty outdoor sensorPossible
If the cable is fine, the sensor may be open circuit. Only measuring it separates the two, not the code.
Evidence: Junkers CerapurComfort ZWBC 25-2 C, instrucciones de instalación y manejo para el técnico · Junkers ZWE 24-3 y 28-3 H A con Bosch Heatronic, instrucciones de instalación
- Sensor set up but not fittedPossible
If your home has no outdoor sensor and CC appears, the technician should check the controller setup; the code only says it is not detected.
Evidence: Junkers CerapurComfort ZWBC 25-2 C, instrucciones de instalación y manejo para el técnico
Virtual technician
Does CC still appear after these checks?
Answer a few questions to narrow down the likely cause and the safest next action. Guidance only - it never replaces a professional.
Sources and technical references
- 1
Junkers CerapurComfort ZWBC 25-2 C, instrucciones de instalación y manejo para el técnico
Junkers (Bosch Termotecnia) · 2012 · manual
- 2
Junkers Cerapur Excellence Compact, instrucciones de uso de la caldera mural a gas de condensación
Junkers (Bosch Termotecnia) · 2019 · manual
- 3
Junkers ZWE 24-3 y 28-3 H A con Bosch Heatronic, instrucciones de instalación
Junkers (Bosch Termotecnia) · 2000 · manual
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