E1 and CA error in Junkerswater heaters: water too hot and excessive flow

Your Junkers shuts off mid-shower and displays E1, or your HydroPower shows CA. These two codes have nothing to do with the gas or the spark: they're related to the water. E1 indicates that the water is too hot (above about 85°C), and CA means that more water is flowing through the heater than it can heat. The good news is that, often, the solution is free.

This guide explains why these errors occur, why E1 is so common in summer or in homes with solar panels, what to check in order, and what the Junkers for each water heater. We also include the FE error code for the HydroPower-Plus.

Error E1: The water is too hot

An instantaneous water heater heats water as it flows. It has a minimum power output below which it cannot be lowered: if very little water flows through, or if the water entering is already hot, even the smallest flame will overheat it. The outlet NTC sensor detects this and the heater shuts off with code E1. These are the causes, from simplest to most expensive:

1. Low flow rate and high temperature

The classic problem: the selector is set to maximum and the tap is only partially open, or a single-lever mixer tap is set to an intermediate position, mixing too much cold water. The water heater receives too little water and overheats it. Try lowering the water heater's temperature and opening the hot water tap more, mixing less water. You'll save gas, and the E1 error code usually disappears.

2. Summer

In summer, the mains water is warmer. The same setting that worked well in winter now causes overheating. That's why many E1 error codes appear in July and disappear on their own in October. Lowering the selector in summer is normal.

3. Water preheated by solar panels

A little-known fact: if you have solar thermal panels and the water from the solar tank enters the water heater without passing through a mixing valve or solar kit, on sunny days the water will already reach 50 or 60 °C. The heater will still turn on, and you'll still get an E1 rating. The solution is a solar kit or a thermostatic valve at the inlet, which will ensure the heater only turns on when needed. This must be installed by a qualified technician.

4. Lime in the heating body

Limescale buildup inside the coil reduces water flow and creates hot spots. This is often accompanied by a "boiling" noise and a decreasing flow rate. The solution is to descale the water heater or replace the coil.

5. The probe or its assembly

If the NTC probe doesn't make good contact with the pipe or is incorrectly installed, it will provide inaccurate readings and may shut off unexpectedly. The Celsius Plus manual specifically mentions incorrectly installed NTC probes as a cause of the device shutting down and locking up. More information can be found in our NTC probe Junkers.

AC error: too much flow (or a turbine that is over-speeding)

In the HydroPower-Plus heater

The HydroPower-Plus operates with flow rates between 1.5 and 30 liters per minute. If 30 liters per minute or more, it will produce a faulty flow rate (CA). In a typical home, it's rare to reach such high flow rates, so the following should be suspected:

• Several hot water taps open at the same time, or a high-flow bathtub tap.
• A major leak in the hot water system.
• Air in the pipe (after a water cut-off): the bubbles make the turbine spin faster than it actually does.
• A damaged flow sensor (turbine) that is over-measuring.

In Eurboilers

In the Eur, the CA (Certificate of Attention) indicates excessively high revolutions per minute (RPM) of the turbine that measures the flow of domestic hot water. The manual instructs that the turbine be checked. First, bleed the air from the system by opening the taps for a while; if the problem persists, check or replace the turbine.

FE Error: Stepper Motor (HydroPower-Plus)

The HydroPower-Plus regulates the gas with a small stepper motor. The " FE" indicates that this motor is disconnected. The first thing to check is its connector and cable; if they are fine, the motor or the electronics need servicing.

What does the Junkers technical manual say about the model?

• miniMAXX (WR-2): E1, over-temperature in the hot water NTC, above 85 °C. The manufacturer indicates lowering the temperature.
• HydroPower-Plus (WTD…KG): E1, over 85 °C. CA, flow rate of 30 l/min or more (working range of 1.5 to 30 l/min). FE, stepper motor disconnected.
• miniMAXX Excellence (WTD…KME): E1, overheating. Wait for it to cool down.
• Celsius / Celsius Plus: The unit shuts down and locks with error code E1 (or C2) due to excessive temperature in the outlet NTC thermistor, incorrectly installed NTC thermistors, or gas venting problems. The manual recommends checking the gas venting, condensation, and probe installation. It will only restart after the cause has been eliminated and the reset button has been pressed.
• Eur(boiler): AC, turbine revolutions too high. Control the turbine.

What you can do (and what you can't)

Yes you can:

• Lower the temperature selector, especially in summer.
• Open the hot water tap more and mix less with the cold water.
• Clean the filters of the taps and the shower head: with low flow, E1 appears sooner.
• Purge the air by opening the taps for a while after a water outage.
• Check for hot water leaks if you get a CA reading.

It's best to have a technician do it: install a solar kit or a mixing valve, descale the coil, change the turbine, or check the stepper motor.

Related spare parts

Flow sensors and turbines:

• Turbine flow sensor for WTD heaters (87070028510)
• ELK-0602 turbine flow meter for WTD and ZWC18/24
• Flow sensor/flow switch WTD11 (87074061300)
• miniMAXX WRD turbine hydro generator (87074060950)
• Turbine hydrogen generator WR11 (87074061040)

Temperature probes:

• Temperature sensor 130 °C WTD11KG (8755005383)
• Temperature probe limiter 104 °C WTD 11 (87072064510)
• NTC hot water probe WTD12 and ZWC24/28 (87160108090)

Coils (body of Chaldea):

• 14 liter coil WRD 14 (87054063850)
• 14 liter WT14 tank coil (87054061980)

More parts available for heater replacements. Always check the reference number of your old part.

Frequently Asked Questions

Is E1 dangerous?

The water heater shuts off precisely to prevent the release of potentially scalding water. It's not dangerous in itself, but if it happens frequently, the cause needs to be investigated.

This only happens to me in the summer. Do I need to fix something?

Probably not: simply lowering the temperature selector during the warmer months is enough. If it still happens with the tap fully open, check the limescale and the sensor.

Why has my water heater been showing E1 since I installed solar panels?

Because it's receiving hot water. You need a solar kit or a thermostatic valve that makes the water heater turn on only when the solar water isn't enough.

My heater won't turn on and isn't giving any code. What should I do?

Check out our guide for water heaters Junkers that won't turn on or are flickering.