- Boilers
- Tankless gas water heater
E1
Junkers E1 on gas water heater: outlet water overheating
Risk level
High
Professional inspection is recommended.
Urgency
High
Quick answer
E1 on Junkers Hydronext 5600S and 5700S water heaters means the outlet water temperature sensor detected overheating and locked the unit. Let the heater cool down, lower the set temperature below 60 °C, reset once by holding reset for 5 seconds, and call a technician if E1 returns.
Safety first
Stop and check this first
- The display shows the temperature leaving the appliance: after an E1 overheat lockout, scalding water may sit in the pipes, so always test the water temperature at the tap before use to prevent burns.
- Never remove the front cover or bypass any temperature sensor or limiter; if you smell gas, close the main gas shut-off valve, open doors and windows without operating any electrical switches, leave the building, and call from outside.
Safe checks you can perform
- Allow the water heater to cool with taps closed
- Read outlet temperature 2d and water flow 3d in menu P4
- Single 5-second reset and hot water test at a lower setpoint
- Inspect outlet sensor, water inlet filter and combustion chamber
Leave these tasks to a qualified professional
- Do not attempt this professional task: Clean or replace the cold water inlet filter and check the flow regulator
- Do not attempt this professional task: Descale the combustion chamber and reassemble with new gaskets
- Do not attempt this professional task: Check the outlet water temperature sensor and burner gas pressure
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.
Clean or replace the cold water inlet filter and check the flow regulator
What they doThe technician shuts off the water supply, drains the heater, removes the fixing screw and flow regulator (or filter cap on the 5700S), replaces the water filter, and reassembles it ensuring the filter is installed.
They must show youthe water filter removed from the inlet pipe and the flow rate reading in parameter 3d after reassembly.
In writingcode E1, the water filter cleaning or replacement, the verified flow rate in l/min, and the date.
Descale the combustion chamber and reassemble with new gaskets
What they doIn medium or high water hardness areas, the technician removes the combustion chamber, descales its interior and connecting pipes, and refits the chamber using new gaskets and O-rings throughout.
They must show youthe descaled waterways and the new gaskets fitted during reassembly.
In writingthe descaling work performed, the gaskets replaced, and the water and gas tightness check.
Check the outlet water temperature sensor and burner gas pressure
What they doThe technician inspects the electrical contacts of the outlet water temperature sensor and temperature limiter to the control box, then verifies burner gas pressure regulation and checks for gas and water leaks.
They must show youthe live outlet temperature reading in parameter 2d under steady flow and the completed leak test.
In writingthe inlet (1d) and outlet (2d) temperature readings, measured gas pressure, and any part replaced with its reason.
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.
Allow the water heater to cool with taps closed
- Who:
- you.
- How:
- close the hot water tap and wait several minutes without drawing water so the heat accumulated in the water heater's outlet pipe dissipates, as the manual instructs for E1.
- Result that matters:
- letting the heat exchanger and outlet pipe cool down before attempting a single reset.
- If the unit has cooled down for several minutes:
- move on to checking the set temperature and the operating data menu.
- If it just locked out after a long draw at maximum temperature:
- wait until it has cooled completely before touching the reset key.
- Evidence to keep:
- how long you let the heater cool and what temperature setpoint was selected when E1 appeared.
Evidence: Junkers Hydronext 5600S WTD12/15/17..., manual de instalación y uso del calentador de gas (6721841217) · Junkers Hydronext 5700S WTD12/15/17..., manual de instalación y uso del calentador de gas (6720884104)
Read outlet temperature 2d and water flow 3d in menu P4
- Who:
- you.
- How:
- press the menu symbol to display P4, enter Od (operating data) and check parameters 2d (current outlet water temperature sensor reading) and 3d (current water flow rate).
- Result that matters:
- seeing what temperature the outlet sensor reports and how many litres per minute flow when a hot tap is opened.
- If 2d drops to a normal value once cool and 3d shows steady flow when a tap opens:
- lower the setpoint with the arrow keys to the minimum needed.
- If 2d still reads abnormally high with the unit cold or 3d barely registers flow:
- write down both readings for the service technician.
- Evidence to keep:
- the values shown under parameters 2d and 3d in submenu Od and the latest fault entry 1F in history menu FH.
Evidence: Junkers Hydronext 5600S WTD12/15/17..., manual de instalación y uso del calentador de gas (6721841217) · Junkers Hydronext 5700S WTD12/15/17..., manual de instalación y uso del calentador de gas (6720884104)
Single 5-second reset and hot water test at a lower setpoint
- Who:
- you.
- How:
- once the heater is cool, hold the reset symbol for 5 seconds as described in the manual's reset section, set the outlet temperature below the 60 °C factory default, and open a hot water tap.
- Result that matters:
- checking whether the E1 safety lockout clears after cooling and operating at a moderate temperature setting.
- If the burner lights and delivers hot water without showing E1:
- keep the temperature set to the minimum comfortable level.
- If E1 returns on the display:
- stop resetting, switch the heater off with the ON/OFF symbol and contact a qualified technician.
- Evidence to keep:
- whether holding reset for 5 seconds cleared E1 and how quickly E1 returned when drawing hot water.
Evidence: Junkers Hydronext 5600S WTD12/15/17..., manual de instalación y uso del calentador de gas (6721841217) · Junkers Hydronext 5700S WTD12/15/17..., manual de instalación y uso del calentador de gas (6720884104)
Inspect outlet sensor, water inlet filter and combustion chamber
- Who:
- qualified gas and plumbing technician.
- How:
- with mains power isolated and gas and water valves closed, test the outlet water temperature sensor and temperature limiter, inspect the water inlet filter, and check the combustion chamber for lime scale.
- Result that matters:
- identifying whether E1 is caused by restricted water flow, scale inside the heat exchanger, or a sensor fault.
- If the inlet filter is dirty or the chamber is scaled:
- replace the water filter, descale the chamber and pipes, fit new gaskets and retest.
- If water flow is unobstructed but the outlet sensor or its wiring is faulty:
- repair the connection or fit an original replacement sensor.
- Evidence to keep:
- measured sensor values, condition of the removed water inlet filter, and confirmation that new gaskets were fitted.
Removing the front cover exposes 230 V live terminals and gas components: authorized technician only with power disconnected.
Evidence: Junkers Hydronext 5600S WTD12/15/17..., manual de instalación y uso del calentador de gas (6721841217) · Junkers Hydronext 5700S WTD12/15/17..., manual de instalación y uso del calentador de gas (6720884104)
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
- Tankless gas water heater
Known code variants
- aire acondicionado Carrier E1
- ALFA Crea E1 error
- ALFA Duo presser foot lifter position error
- ALFA E1
- Aviso E1
- Bosch E1
- cabezal tado E1
- calentador Junkers E1
- Carrier AC E1
- Carrier E1
- Carrier E1 error
- Carrier mini split E1
- Carrier XPower E1
- Cecofry E1 code
- Cecotec ForceClima E1
- Cecotec portable AC E1 code
- Circuito abierto en monitor de temperatura
- Code E1
- Código de error E1
- Código E1
- codigo E1 aire acondicionado Cecotec
- Código E1 Cecofry
- Cosori E1
- Culligan E1
- Culligan ERR 1
- Culligan softener E1
- descalcificador Culligan E1
- Display E1
- Display shows Error Code E1
- E 1
- E-1
- E01
- E1
- E1 cestillo izquierdo
- E1 common wire required
- E1 fan error
- E1 left basket sensor
- E1 on display
- E1 sensor de temperatura
- E1 temperature sensor
- E2
- E3
- E4
- Electrolux ELAC309W E1
- Electrolux washer E1
- Electrolux washing machine error E1
- Elevador de prensatelas posición incorrecta
- EMPTY GRATE AND PRESS ON-OFF
- ERR 1
- ERR1
- Error 1 Culligan
- Error Code E1
- Error E1
- error E1 ALFA Crea
- error E1 calefón Rheem
- error E1 calentador Rheem
- error E1 Carrier
- error E1 lavarropas Electrolux
- error E1 lavavajillas Midea
- error E1 lavavajillas Smeg
- error E1 lavavajillas Teka
- error E1 purificador Philips
- error E1 sensor temperatura tubo Cecotec
- error E1 tado calibración
- falla de encendido E1 Rheem
- falla E1 lavadora Electrolux
- Fallo del motor E1
- Fallo del sistema de bloqueo
- ForceClima 12850 Style E1
- ForceClima 7900 SmartTouch E1
- ForceClima 9900 SmartTouch E1
- ForceClima E1 tube condenser sensor fault
- Hydronext 5600S E1
- Hydronext 5700S E1
- Junkers E1
- Junkers water heater E1
- La pantalla muestra el código de error E1
- lavavajillas Midea E1
- lavavajillas Smeg aguastop E1
- Levoit E1 motor malfunction
- Lock system fault
- MDWEB1004LS E1
- MFD45S200 E1
- Midea dishwasher E1
- Midea dishwasher error E1
- Midea E1
- minisplit Carrier E1
- Nest E1
- Nest E1 C wire
- Nest E1 cable C
- Nest thermostat E1
- Open circuit in temperature monitor
- Philips AC3033 E1
- Philips AC3036 E1
- Philips AC3039 E1
- Philips air purifier E1
- Philips E1
- Philips Series 3000i E1 motor malfunction
- Posición del prensatelas posición incorrecta
- Presser foot lifter wrong position
- purificador Philips E1
- Rheem E1
- Rheem gas water heater E1
- Rheem ignition failure E1
- Rheem R7-14L E1
- Smeg Aquastop failure
- Smeg avería aguastop
- Smeg dishwasher anti-flooding E1
- Smeg dishwasher E1
- Smeg dishwasher error E1
- Smeg lavavajillas E1
- Smeg LVFABCR3 E1
- tado Basic dos rayas llave inglesa
- tado Basic two dashes spanner
- tado E1
- tado E1 calibration error
- tado radiator thermostat E1
- tado Smart Radiator Thermostat E1
- tado° E1
- Teka dishwasher E1
- Teka dishwasher error E1
- Teka DW8 E1
- Teka lavavajillas E1
- Teka LP8 E1
- termostato Nest E1
- Warning E1
What it means
In the installation and user manuals for the room-sealed Junkers Hydronext 5600S and 5700S gas water heaters (tables 19 and 20), code E1 indicates that the outlet water temperature sensor has detected overheating. Like all fault codes shown on the display, E1 triggers a safety lockout that shuts down the burner until the problem is resolved and the appliance is reset. Seeing E1 on the screen does not by itself prove that the temperature sensor or any other component is defective.
Warnings and stop conditions
- Highsource verified
The display shows the temperature leaving the appliance: after an E1 overheat lockout, scalding water may sit in the pipes, so always test the water temperature at the tap before use to prevent burns.
Evidence: Junkers Hydronext 5600S WTD12/15/17..., manual de instalación y uso del calentador de gas (6721841217) · Junkers Hydronext 5700S WTD12/15/17..., manual de instalación y uso del calentador de gas (6720884104)
- Highsource verified
Never remove the front cover or bypass any temperature sensor or limiter; if you smell gas, close the main gas shut-off valve, open doors and windows without operating any electrical switches, leave the building, and call from outside.
Evidence: Junkers Hydronext 5600S WTD12/15/17..., manual de instalación y uso del calentador de gas (6721841217) · Junkers Hydronext 5700S WTD12/15/17..., manual de instalación y uso del calentador de gas (6720884104)
Symptoms and causes
Probable causes · in order
- Temporary heat build-up at the hot water outletCommon
The manual's first remedy for E1 is to let the appliance cool down and try again, as residual heat in the outlet pipe after hot water draw-offs can push the outlet sensor past its limit.
Evidence: Junkers Hydronext 5600S WTD12/15/17..., manual de instalación y uso del calentador de gas (6721841217) · Junkers Hydronext 5700S WTD12/15/17..., manual de instalación y uso del calentador de gas (6720884104)
- High temperature setting with low flow or scale build-upPossible
Running at the 60 °C factory default with restricted water flow or lime deposits inside the combustion chamber raises outlet water temperature until the E1 safety lockout trips.
Evidence: Junkers Hydronext 5600S WTD12/15/17..., manual de instalación y uso del calentador de gas (6721841217) · Junkers Hydronext 5700S WTD12/15/17..., manual de instalación y uso del calentador de gas (6720884104)
- Clogged cold water inlet filter or throttled flow regulatorPossible
Debris trapped in the cold water inlet filter or a flow regulator turned too far down reduces water circulation through the heat exchanger and leads to overheating.
Evidence: Junkers Hydronext 5600S WTD12/15/17..., manual de instalación y uso del calentador de gas (6721841217) · Junkers Hydronext 5700S WTD12/15/17..., manual de instalación y uso del calentador de gas (6720884104)
- Faulty outlet water temperature sensor or wiring contactLess common
A defect in the outlet water temperature sensor (item 9 on the wiring diagram) or corrosion on its electrical contacts to the control box can report a false overheat condition.
Evidence: Junkers Hydronext 5600S WTD12/15/17..., manual de instalación y uso del calentador de gas (6721841217) · Junkers Hydronext 5700S WTD12/15/17..., manual de instalación y uso del calentador de gas (6720884104)
Virtual technician
Does E1 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 (Bosch Termotecnia) · 2022 · manual
- 2
Junkers (Bosch Termotecnia) · 2021 · manual
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