- Boilers
- Gas boiler
H11
Junkers H11 on a gas boiler: hot water outlet sensor warning
Risk level
Medium
Proceed carefully and stop if the check is unclear.
Urgency
Medium
Quick answer
Junkers H11 is a warning, not a lockout: the hot water outlet sensor is faulty and the boiler still gives hot water with less control. Test the water before showering and book a visit from the installer or service.
Safety first
Stop and check this first
- If you smell gas: Bosch says do not smoke or use lighters, do not operate electrical switches or use the phone or doorbell, close the gas valve at the meter or regulator, open doors and windows, warn the neighbours and leave the building. Call your gas distributor's emergency number from the street.
- With H11 the boiler supplies hot water with less temperature control, according to Bosch. Test the water with your hand before showering or bathing children or older people until the technician checks the sensor.
Safe checks you can perform
- Gas or flue gas smell near the boiler
- When H11 appears and how the water comes out
- Temperature setting and tap flow
- Hot water sensor by the technician
Leave these tasks to a qualified professional
- Do not attempt this professional task: Hot water outlet sensor measurement
- Do not attempt this professional task: Sensor position and connection
- Do not attempt this professional task: Information menu reading
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 outlet sensor measurement
What they doThe technician measures the hot water NTC sensor and compares it with the manufacturer's table to tell an open circuit from a short circuit.
They must show youthe reading on the meter.
In writingthe value measured against the manufacturer's specification.
Sensor position and connection
What they doChecks that the sensor sits in its housing and that the connector and wire are sound, as the poor installation status in Bosch's list suggests.
They must show youa photo of the sensor and its connector.
In writingwhat was found and what was corrected.
Information menu reading
What they doReads i1 current status and i2 last error to see which three digit number comes with H11 and whether it repeats with other codes.
They must show youthe display with the last error.
In writingthe codes and cause numbers read.
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.
Gas or flue gas smell near the boiler
- Who:
- you.
- How:
- walk up without pressing switches or turning lights on and notice whether there is a smell of gas or combustion fumes.
- Result that matters:
- whether there is a smell or not.
- If there is a smell:
- do not touch the boiler and follow the gas warning on this page.
- If there is no smell:
- go on to note the warning.
- Evidence to keep:
- the time and what you noticed.
Evidence: Junkers Cerapur Excellence Compact, instrucciones de uso de la caldera mural a gas de condensación
When H11 appears and how the water comes out
- Who:
- you.
- How:
- take a photo of the display showing H11 and open a hot tap; notice whether the temperature goes up and down or does not hold.
- Result that matters:
- whether the hot water is steady or variable.
- If it varies a lot:
- that is the reduced control Bosch describes; use the water carefully.
- If it appeared right after a repair:
- tell the technician, it points to a badly placed sensor.
- Evidence to keep:
- a photo of the display, the date and how the water came out.
Evidence: Junkers Cerapur Excellence Compact, instrucciones de uso de la caldera mural a gas de condensación · Junkers Cerapur Excellence Compact ZWB...A..., instrucciones de instalación y manejo para el técnico (6 720 820 575)
Temperature setting and tap flow
- Who:
- you.
- How:
- check the hot water temperature set on the boiler control and open the tap at a moderate flow, as Bosch's fault table suggests.
- Result that matters:
- whether the water improves when you adjust temperature or flow.
- If it improves:
- part of the problem was the setting; H11 still needs checking.
- If nothing changes:
- the fault is in the sensor and the technician fixes it.
- Evidence to keep:
- the temperature set and the result.
Evidence: Junkers Cerapur Excellence Compact, instrucciones de uso de la caldera mural a gas de condensación
Hot water sensor by the technician
- Who:
- authorised technician.
- How:
- checks the position of the hot water outlet sensor, its connector and wiring, and measures the sensor.
- Result that matters:
- whether the sensor is open, shorted or badly placed.
- If it is badly placed or the connector is loose:
- it is refitted or tightened and tested.
- If the reading is outside the specification:
- the sensor is replaced.
- Evidence to keep:
- a report with the reading, a photo of the connector and the part replaced.
Bosch reserves removing the casing and any internal work for a competent technician. Sensors, pump and board are inside, next to mains voltage parts.
Evidence: Junkers Cerapur Excellence Compact ZWB...A..., instrucciones de instalación y manejo para el técnico (6 720 820 575)
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
- Aviso H11 Junkers
- Cerapur H11
- Error H11 Junkers
- H 11
- Junkers H11
- Panasonic H11
What it means
On the Cerapur Excellence Compact, codes with an H are maintenance warnings: the boiler keeps working but a function needs attention. H11 is a fault in the hot water outlet sensor: hot water can still be supplied, but with less control. Bosch gives three situations: sensor open circuit, sensor short circuit or sensor out of position. The status list also includes hot water sensor defect and poor installation of the sensor. The warning does not say which of the three it is.
Warnings and stop conditions
- Criticaleditorial warning
If you smell gas: Bosch says do not smoke or use lighters, do not operate electrical switches or use the phone or doorbell, close the gas valve at the meter or regulator, open doors and windows, warn the neighbours and leave the building. Call your gas distributor's emergency number from the street.
Evidence: Junkers Cerapur Excellence Compact, instrucciones de uso de la caldera mural a gas de condensación
- Mediumeditorial warning
With H11 the boiler supplies hot water with less temperature control, according to Bosch. Test the water with your hand before showering or bathing children or older people until the technician checks the sensor.
Evidence: Junkers Cerapur Excellence Compact ZWB...A..., instrucciones de instalación y manejo para el técnico (6 720 820 575)
Symptoms and causes
Probable causes · in order
- Open sensor or wiringPossible
Bosch names an open sensor. It is a broken circuit, such as a loose connector or a cut wire, and only the technician can tell by measuring.
Evidence: Junkers Cerapur Excellence Compact ZWB...A..., instrucciones de instalación y manejo para el técnico (6 720 820 575)
- Sensor short circuitPossible
Bosch's second situation is a short circuit. Unlike an open circuit, the technician reads a value near zero instead of an infinite one.
Evidence: Junkers Cerapur Excellence Compact ZWB...A..., instrucciones de instalación y manejo para el técnico (6 720 820 575)
- Sensor out of positionPossible
Bosch names the sensor out of position and the status list mentions poor sensor installation. It fits if H11 appeared after a repair or service.
Evidence: Junkers Cerapur Excellence Compact ZWB...A..., instrucciones de instalación y manejo para el técnico (6 720 820 575)
Virtual technician
Does H11 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 Cerapur Excellence Compact, instrucciones de uso de la caldera mural a gas de condensación
Junkers (Bosch Termotecnia) · 2019 · manual
- 2
Junkers (Bosch Termotecnia) · 2019 · manual
Was this entry useful?