- Boilers
- Gas boiler
A7
Junkers A7 on a gas boiler: hot water temperature sensor fault
Risk level
Medium
Proceed carefully and stop if the check is unclear.
Urgency
Medium
Quick answer
Junkers A7 means the boiler reads the domestic hot water temperature sensor as faulty. It usually affects hot water, not the gas side. Reset once and, if it stays, call the service centre.
Safety first
Stop and check this first
- Bosch tells installers to warn the customer not to modify or repair the appliance. Do not open the casing to check the sensor.
Safe checks you can perform
- Reset or power cycle
- Heating versus hot water
- Sensor and cable measurement
Leave these tasks to a qualified professional
- Do not attempt this professional task: Hot water NTC measurement
- Do not attempt this professional task: Hot water test after the repair
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.
Hot water NTC measurement
What they doThe technician measures the sensor resistance with a multimeter and compares it with the manufacturer's curve.
They must show youthe measured value against the curve.
In writingwhat was measured and what was replaced.
Hot water test after the repair
What they doAfter the repair, the technician opens a hot tap and checks the boiler controls the temperature without showing A7.
They must show youwater coming out at the set temperature.
In writingthe date and result.
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.
Reset or power cycle
- Who:
- you.
- How:
- if the reset key is flashing, hold it; otherwise switch the boiler off and on, as Bosch says for faults.
- Result that matters:
- whether A7 clears and hot water comes out at a normal temperature.
- If it clears and does not return:
- note the date; it may have been a one-off.
- If A7 returns:
- Bosch says to contact the official service centre with the code.
- Evidence to keep:
- a photo of the display and a note of whether there was hot water.
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
Heating versus hot water
- Who:
- you.
- How:
- check whether heating still works and whether the problem appears only when you open a hot tap.
- Result that matters:
- which service fails with A7 on the display.
- If only hot water fails:
- it fits a fault in the hot water circuit, as Bosch describes.
- If everything fails:
- tell the technician; there may be another fault besides A7.
- Evidence to keep:
- a note of what worked and what did not.
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 measurement
- Who:
- official service technician.
- How:
- measures the hot water sensor and checks the cable for continuity and shorts, as Bosch requires.
- Result that matters:
- whether the sensor is within its curve and the cable is neither open nor shorted.
- If the sensor is off the curve:
- that confirms the sensor.
- If the sensor measures fine:
- it points to the cable or connector.
- Evidence to keep:
- a report with the measured values.
The sensor is inside the boiler, next to mains voltage and gas: the technician measures it.
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
- A07
- A-7
- Bosch A7 caldera
- Cerapur A7
- Error A7 Junkers
- Junkers A7
What it means
On the CerapurComfort, A7 is "hot water temperature sensor defective", and Bosch's fix is to check the sensor and its connecting cable for continuity or a short to earth. The ZWE manual describes the same code as an open hot water NTC. In other words, the control reads an impossible value in the hot water circuit. It can be the sensor, the cable or the connector; the code does not say which nor prove the sensor is broken.
Warnings and stop conditions
- Mediumsource verified
Bosch tells installers to warn the customer not to modify or repair the appliance. Do not open the casing to check the sensor.
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
Symptoms and causes
Probable causes · in order
- Damaged hot water NTC sensorCommon
Bosch asks for the sensor to be measured. If its value is off the curve with a good cable, the sensor is the cause.
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
- Cable or connector open or shortedPossible
Bosch names the connecting cable explicitly. A chafed cable or corroded connector gives the same reading; a continuity test shows it.
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
Virtual technician
Does A7 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 ZWE 24-3 y 28-3 H A con Bosch Heatronic, instrucciones de instalación
Junkers (Bosch Termotecnia) · 2000 · manual
Was this entry useful?