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Rainwater harvesting is no longer just a fashionable topic. Toilet flushing, washing water, garden irrigation or spraying – if you have a storage tank or cistern on your property, the question is not whether to use rainwater, but how to get it out. Wilo-Extract FIRST is a multistage submersible pump designed precisely for this scenario: a single unit replaces the pump, pressure switch, dry-running protection and automatic control. Whether you are looking for a pump for an underground sump or a dug well, Wilo-Extract FIRST may be the right solution.
Author: Bc. Jaromír Bittner
It is a fully submersible, multistage, self-venting submersible motor pump intended for domestic cisterns, storage tanks and shallow wells. It has a close-coupled design, hydraulics formed by radial impellers in multiple stages, and a motor cooled by the pumped medium. This is an important detail: in the SE version, cooling by the medium allows installation in a dry sump outside the tank itself.
The pump is primarily intended for service water and rainwater. Permitted media include clean water, service water and cold water up to 40 °C. By contrast, it is not intended for drinking water, swimming pool drainage or continuous operation longer than 2 hours (for example, fountain operation reduces pump service life).
Wilo offers FIRST in four versions differing in the number of stages and the suction arrangement:
Versions without the SE designation are standard submersible pumps with a suction strainer on the underside of the casing – they are installed directly in the cistern. SE versions have a side suction port to which a floating suction filter (hose with float) is connected, drawing water from the optimum depth below the surface. This has two advantages: water is taken from a cleaner layer away from the sediment at the bottom, and the pump itself can be placed in a dry sump next to the tank.
Technical parameters
In terms of materials, the pump is built from a combination of reinforced polyphenylene oxide (PPO GF20 and GF30 for the casing and hydraulics), AISI 304 stainless steel (cooling jacket, shaft) and aluminium (motor housing). The mechanical seals are carbon/ceramic, with NBR static seals.
A clever detail: between the two mechanical seals there is an oil chamber that captures any leakage before water can reach the motor.
The key difference compared with a standard submersible pump is the integrated electronics. The user does not need to buy a separate pressure switch, dry-running protection or automatic controller. It works like this:
The pressure setting is factory-sealed – the controller must not be adjusted.
Wet installation (standard). The pump hangs directly in the tank in a vertical position, suspended by a safety rope from the handle and at the same time secured via the discharge pipework. Two distances are important:
The pump must not touch the bottom – this would transmit noise and vibration. It must also not be installed horizontally.
Dry installation (SE versions only). The pump stands outside the tank and draws water through a hose with a floating filter connected to the side G1 port. During operation, the motor is cooled by the flowing medium, so immersion is not required. Please note: the self-venting valve in the upper part of the casing lets through a small amount of water in this installation, and this is not a fault. For this reason, Wilo recommends dry installation outdoors only, not in a plant room.
Before the first start-up of the SE version, fill the suction hose with water – Extract FIRST is not self-priming.
On the discharge side, use either steel pipes with fittings or semi-rigid PE pipes. The pipe diameter must not be smaller than the G1 connection on the pump – any reduction will lower performance. When installing on semi-rigid pipes, the pump must be suspended by the handle using a safety rope so that the weight is carried by the rope and not by the pipework.
Electrically, four conditions apply:
The connection must be carried out by an electrician in accordance with Czech standards. On the single-phase version, rotation direction is not an issue – it cannot be connected incorrectly.
In practice, none. Wilo states that the pump does not require regular maintenance. If performance drops, the first step is to remove the pump and clean the suction strainer with a soft brush under water. Everything else – replacement of mechanical seals, electronics repair, cable replacement – should be left to a service technician.
The most common cause of actual faults is sand and sediment, which clog the hydraulics. If your source (especially a shallow well) contains more than 50 g of sand per m³, you need to install a pre-filter or choose a different type of pump.
The troubleshooting table in the manual reveals the typical problems:
Yes, that is exactly what the range is designed for – using rainwater for toilets, washing machines and irrigation in detached and semi-detached houses. However, you must not use it for drinking water.
The number of hydraulic stages and the output. The three-stage (303) version has 0.75 kW and a start pressure of 2 bar, while the four-stage (304) version has 1.0 kW and a start pressure of 2.5 bar. The four-stage version delivers higher pressure and is better suited to multi-storey houses or longer pipe runs.
The side suction port allows connection of a floating filter, which draws water from the cleaner upper layer of the tank (rather than from the bottom with sediment). In addition, you can install the pump dry next to the cistern – for example in an outdoor service chamber.
No. In dry-sump installation for the SE version, the suction hose must be filled with water manually before first start-up. With wet installation, this issue does not arise because the pump is submerged.
5 metres. A deeper cistern or well is no longer suitable for this range.
By integrated electronics – the pump detects for itself that there is nothing to pump and switches off. There is no need to buy an external float switch.
No. The manufacturer expressly prohibits power supply from off-grid inverters due to the risk of overvoltage. If you want to run it from a solar source, you must have a hybrid system with surge protection or grid compatibility.
Check the discharge side for leaks (non-return valve, fittings, taps) and check the pre-charge pressure of the pressure vessel. If you have a small expansion vessel, consider replacing it with a larger one – this will reduce the number of starts and extend service life.
Under normal operation, practically never. If the flow rate drops, remove the pump and clean the suction strainer with a brush under running water. The Kickoff function itself briefly starts the pump once every 24 hours to prevent dirt from sticking together.
The installation location must be protected against frost. If the cistern is underground below the frost line, this is not a problem. For outdoor dry installation, the discharge line, shut-off valve and electrical enclosure must be insulated – otherwise there is a risk of the pipework bursting.
A shut-off valve on the discharge side (for servicing without draining the pipework), a coarse or fine floating filter for the SE version, and an external pressure vessel if you want to reduce the number of starts.
Sources: Wilo-Extract FIRST technical manual (edition 2022-10, production number 6094303), Wilo product sheet and the manufacturer’s catalogue data.
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