The EHEIM ThermoPreset aquarium heater allows you to maintain the aquarium water at a constant temperature without needing to adjust it. ThermoPreset is a heater for both freshwater and marine aquariums, pre-set to 25 °C to keep the water at a stable temperature. Very durable and featuring a sleek, minimalist design, it is barely visible in the aquarium thanks to its compact size. Available in 4 power levels, it is suitable for aquariums ranging from 25 L to 400 L.

Form Factor & Materials

• The heater is slim and compact: it has a diameter of about 28.2 mm (2.82 cm)

• Its length (for the 200 W variant) is approximately 253.5 mm (25.35 cm)

• The heater body features an additional plastic protective cover (or shield) that enhances mechanical strength and protects against breakage.

• It is built for full submersion (i.e., it's submersible) and can be used in both fresh and salt water.

Safety Features

• Uses an electronic control system (rather than purely mechanical) to maintain the temperature with high accuracy.

• Includes a dry-run protection (also called "dry-running protection") that guards against overheating in the event the heater is exposed (e.g. water level drops) or running “dry.”

• Has an LED indicator light to show when the heating function is active.

• Comes with suction cups for secure mounting to the aquarium wall.

Technical Specifications

• The heater operates at 200 watts of power on standard 50 Hz mains.

• It has a preset temperature of 25 °C, which cannot be adjusted.

• Temperature stability is high, thanks to its electronic control system that minimizes fluctuations.

• The diameter of the heater body is about 28.2 mm (2.8 cm).

• The length of the 200 W model is roughly 253.5 mm (25.3 cm).

• It is suitable for aquariums of up to 300–400 litres, depending on ambient conditions.

• It can be used in both freshwater and saltwater aquariums.

• The heater is fully submersible and comes with suction cups for easy installation.

• It has a built-in LED indicator showing when heating is active.

• The device features dry-run protection to prevent overheating if the water level drops.

• It is backed by a three-year manufacturer’s warranty.

Advantages of using Thermopreset 200 W Heater 

1. Ease of Use (Preset Temperature)
   Because the temperature is already fixed at 25 °C, there’s no adjustment needed. This reduces human error in setting thermostats incorrectly.

2. High Stability & Accuracy
   The electronic control helps keep temperature fluctuations to a minimum, which is beneficial for sensitive aquatic species.

3. Robust Protection & Safety Features
   The plastic protective cover helps with mechanical durability. The dry-run protection ensures safety in scenarios like water level drops. The LED indicator gives a visual cue of operation.

4. Compact & Discreet
   Its slim profile makes it less obtrusive in the aquarium setting, especially in smaller tanks where visibility of equipment is a concern.

5. Versatility
   Works in both fresh and saltwater, broadening its usability in different types of aquaria.

6. Trusted Brand / Warranty
   EHEIM is a well-known brand in aquatic equipment, and offering a 3-year guarantee boosts reliability and consumer confidence.

Limitations & Considerations

• Fixed Temperature
  The inability to adjust the temperature might be limiting if your aquarium inhabitants require temperatures significantly higher or lower than 25 °C. If you need, e.g., 27 °C or 24 °C, this heater won’t allow that flexibility.

• Capacity Matching
  Though it’s rated for up to 300–400 L, performance depends on other factors (ambient temperature, insulation, tank placement). If your tank is very deep or poorly insulated, 200 W might strain to maintain the set temperature in colder climates.

• Visibility & Placement
  Even though it’s slim, the roughly 25 cm length means careful placement is needed to make it as invisible as possible.

• Dependence on Electronic Control
  If the electronic thermostat or control circuits fail, you're left without a fallback. But EHEIM’s warranty and build quality aim to mitigate that risk.

• Dry-Run Activation Timing
  The dry-run protection will act only when conditions for dry-running are met (e.g. insufficient water coverage). Users must ensure proper submersion depth and monitor water levels.

Use & Installation Tips

• Mount the heater vertically or slightly angled using the suction cups, ensuring it’s fully submerged and not obstructed by substrate or décor.

• Place it near gentle water circulation so heat distributes evenly.

• During water changes or draining, always ensure the heater stays submerged or is powered off to avoid dry-run damage.

• Monitor the LED indicator as a quick check: if it’s on, the heater is actively heating; if off for long periods in cold conditions, something might be wrong.

• Although preset, occasionally verify your aquarium’s actual temperature with an independent high-quality thermometer, to confirm calibration and operation.