Retrofitting an immersion heater:
How to use surplus solar power for hot water
As of August 2026
Retrofitting an immersion heater: What you should know beforehand
Before ordering, you should check whether the storage, connection, installation space, power supply, and network are compatible with your setup. Here you will find the most important requirements, installation steps, and the setup for surplus power control.
PREREQUISITES
What your storage must provide
A retrofit is possible if your domestic hot water or buffer tank has a suitable connection, sufficient space for the immersion heater, and approval for a screw-in immersion heater.
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01
The connection
The novolto immersion heater has a G 1½-inch connection thread. An available matching sleeve is ideal. For storage tanks with an inspection opening, a suitable flange adapter can be an alternative, depending on the design.
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02
The attic
novolto offers immersion heaters for hot water and buffer storage tanks made of stainless steel or enamel. Nevertheless, always check the manufacturer's approval, the installation position, and the available installation space of your storage tank.
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03
The infrastructure
At the installation site, you need a suitable grounded outlet as well as Wi-Fi or LAN reception. For automatic PV operation, you additionally require a compatible measuring device for the electricity meter data.
SELECT SERVICE
Select the appropriate service
The decisive factors are your typical usable surplus solar power, the heat demand, and the electrical layout at the installation site. The P2300 operates at up to 2,300 watts, the P3000 at up to 3,000 watts; both are adjustable and can adapt their output to the available surplus.
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2.3 kW
novolto P2300
View P2300Up to 2,300 watts of heating power. Useful if your available PV surpluses are generally in the lower power range or if you wish to deliberately limit power consumption to 2.3 kW.
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3.0 kW
novolto P3000
View P3000Up to 3,000 watts of heating power. Useful if higher PV surpluses are regularly available and the existing circuit is suitable for the higher output.
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ADJUSTABLE OUTPUT
Also make use of smaller surpluses
The output can be finely adjusted to the available surplus solar power. This means that full rated power does not have to be available before solar power can be used for hot water.
COSTS & AMORTIZATION
How much does retrofitting cost – and when is it worth it?
The total costs depend on the immersion heater, the chosen electricity meter, and, if applicable, a flange adapter. You can find current device prices on the product pages.
The novolto 230 V models are connected via a standard earthed socket. If changes to the fixed electrical installation are necessary, they must be carried out by a qualified electrician. In case of uncertainty regarding the plumbing side, a specialist HVAC company should take over.
Whether retrofitting is worthwhile depends on the usable surplus solar power, feed-in tariff, avoided heating costs, and total investment. You can find the example calculation in the guide “Is an immersion heater worth it?”.
ASSEMBLY
Installing the immersion heater in six steps
The overview follows the six installation steps of the installation and operating manual. You can find safety information and details in the complete manual.
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01
Prepare storage
Disconnect the heating system from the power supply, shut off the cold water supply, drain the pressure, and empty the storage tank down to the installation level. Then, make the sleeve for the G 1½-inch threaded connection accessible.
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02
Check installation position and insert
The immersion heater may only be installed horizontally; the installation depth of the storage tank must be at least 450 mm. Insert the immersion heater horizontally through the socket and only carefully compress the immersion heaters slightly if necessary.
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03
Seal and tighten
Use the included sealing ring and seal the thread with a suitable sealant such as hemp or PTFE. Tighten only by the designated hexagon; tightening torque: 60 Nm. Do not twist the housing while screwing it in.
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04
Fill storage and check for leaks
Close the drain and open the cold water supply. After filling, immediately check the installation site for leaks and then check it regularly. The novolto immersion heater remains disconnected from the power supply until step 6.
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05
Align housing
Carefully align the rotatable housing part via the shortest path. The power cable should run perpendicular to the floor, the LED display should be horizontal, and the ventilation slots should face the floor.
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06
Establish power supply
Only connect the power plug to the designated earthed socket once the heating elements are completely submerged in water. Upon starting, the system LED lights up solid green for several seconds.
SETUP & APP
Ready in eight steps
After installation, you set up the network, user account, target temperature, and, if required, the automatic surplus solar power control.
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01
Activate connection mode
Hold the connection button for one second. The connection LED will flash blue and the immersion heater will provide an access point whose name begins with "NOVOLTO-".
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02
Connect to NOVOLTO-Wi-Fi
Open the Wi-Fi settings on your smartphone, tablet, or computer, select the access point "NOVOLTO-…", and establish the connection.
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03
Scan QR code no. 1
Scan the provided QR code no. 1. Alternatively, open 192.168.2.1 in your browser. This will take you to the immersion heater's network setup.
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04
Connect to home network
Follow the instructions, select the desired Wi-Fi network and connect. When the connection is successful, the connection LED flashes green slowly.
Alternatively via LAN: Disconnect the immersion heater from the power supply, plug in the LAN cable, and only then reconnect the power plug.
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05
Scan QR code no. 2
Scan the included QR code no. 2 with an internet-enabled device. The novolto app will open, and the serial number and PIN will be pre-filled automatically.
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06
Complete registration
Enter your name and email address, set a password, and complete the necessary confirmations. If you do not have a QR code, you can open novolto.app and enter the serial number and PIN manually.
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07
Set target temperature
Set the desired target temperature for the domestic hot water or buffer tank. Please note that high water temperatures can lead to scalding.
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08
Connect excess measurement
Check compatibilityTo use automatic mode, connect a supported measuring device in novolto. Depending on your setup, this includes supported solutions from Tibber, powerfox, and Shelly. Please check the compatibility of your specific meter or measuring device beforehand.
A suitable MQTT-based system is also an option.
LED DISPLAYS
Device status at a glance
The three LEDs indicate connection, system status, and heating operation directly on the device.
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CONNECTION
LED connection
Pulsing blue: Wi-Fi access point active.
Blue: Network connection established, novolto server unreachable.
Pulsing green: Connected to network and novolto server.
Red: No network connection. -
SYSTEM
LED system
Green: Device starting.
Pulsing green: Normal operation.
Pulsing blue: Firmware update in progress.
Red: Temperature sensor or power control malfunction – contact support. -
HEATING MODE
LED heater
Green: Heating active.
Pulsing green: Heating inactive, no surplus reported.
Pulsing blue: Target temperature reached, heating inactive.
Red: Safety temperature limiter (STL) triggered.
SURPLUS MANAGEMENT
This is how the system works
There are several compatible readers available for surplus management – and you can choose between automatic and manual mode.
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COMPATIBILITY
Compatible electricity readers
Check compatibilityFor surplus management, supported solutions from Tibber, powerfox, and Shelly are options. Always check the compatibility of your specific meter or measuring device before making a selection.
A suitable MQTT-based system is also an option.
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AUTOMATIC
Only use genuine surplus
In automatic mode, the heating output is based on the measured surplus data. The goal is to utilize the actually available surplus solar power as much as possible and avoid unnecessary power grid consumption.
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MANUAL
Heat selectively when needed
In manual mode, you set the power and duration yourself. You can draw power from the grid during this time. For technically savvy users, local control via MQTT is also available.
COMMON ERRORS
You should avoid these mistakes
Typical errors include dry running, incorrect installation position, a leaky screw connection, or a power selection that does not account for the circuit and surplus profile.
Check the storage tank clearance and installation dimensions before ordering. If you are uncertain about the storage tank installation, consult an HVAC specialist.
FURTHER LINKS
Products and instructions
Here you will find the immersion heater models, the appropriate power reader, and the complete installation instructions.
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Immersion heater
View immersion heaterCompare models, technical data, and the right output for your system.
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Electricity reader supported measurement solutions
Check your measurement setupRead your electricity meter, detect surplus energy, and check compatibility with your meter.
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INSTRUCTIONS
Instructions for immersion heater and sensor
Immersion heater manual (German)
Installation, safety, network connection, and operation for the novolto P2300 and P3000.
Open immersion heater manual → (German)For automatic control, check that your chosen measurement device and integration are supported by novolto. Contact us if you need help confirming compatibility.
FAQ
Frequently Asked Questions
Can I retrofit an immersion heater myself?
Yes, provided there is a suitable installation opening and you follow the installation instructions. The novolto 230 V models are connected electrically via a grounded socket. If you are unsure about the water connection, a professional HVAC contractor should handle the installation.
Can an immersion heater also be installed in buffer tanks, domestic hot water tanks, or boilers?
This depends on the storage tank. A suitable G 1½-inch sleeve or adapter solution, sufficient installation space, and approval of the storage tank for a screw-in immersion heater are required.
Do I need an electrician?
The novolto 230 V models are connected to a suitable earthed socket and do not require fixed wiring. If the circuit or the fixed electrical installation needs to be modified, a registered electrical installation company is required.
Which electricity meters are compatible with surplus management?
Supported devices include compatible solutions from Tibber, powerfox, and Shelly. Please check the current compatibility information before making your selection.
A suitable MQTT-based system is also an option.
Is an immersion heater even still worth it?
That depends on your system. The deciding factors are the usable surplus solar power, your actual feed-in tariff, the avoided heating costs, and the total investment. Therefore, there is no blanket amortization period.
Can I also operate the immersion heater locally without the cloud?
Yes. For technically proficient users, local control via MQTT is possible. The currently required MQTT settings are provided by novolto upon request.
Immersion heater and power reader bundle
Combine the appropriate immersion heater with a compatible power reader and start utilizing your surplus energy right away.
