Common problems with pits and pumping units: causes and solutions

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Common problems with manholes and pumping units: causes and solutions

Manholes and pumping units are among those parts of home infrastructure that most homeowners don't think about until something goes wrong. And when they stop working, it's usually not at the best time – in the cold winter, during heavy rain, or exactly when the household needs water or when the sewer must safely remove waste. From experience, we know that most failures are not random – they have specific causes that can be identified, removed, and prevented in the future. This article will help you understand what is happening inside the manhole, why pumping units fail, and what you can do – either yourself or with the help of a professional.

Why manholes and pumping units fail – a basic overview

Before we dive into specific problems, it is important to understand the environment in which these devices operate. A manhole is usually located 1.5 to 3 meters underground, constantly exposed to moisture, soil pressure, temperature fluctuations, and – in the case of pumping manholes – permanent contact with sewage water. These are conditions that would shorten the lifespan of most technical equipment. Add occasional negligence during installation, underestimating regular maintenance, and the choice of unsuitable components, and you have a recipe for failures.

Failures can be divided into three basic groups:

Mechanical failures – damage to the manhole shell, lid, inlet collar, pump, or check valve
Hydraulic failures – poor flow, air pockets in the pipe, backflow, fluctuating pressure
Electrical/control failures – failure of the float switch, control unit, cables, relays, or circuit breakers

Each of these groups has its own symptoms and diagnostic procedures. We will go through them in detail.

Mechanical failures of manholes – what breaks, where and why

Damage to the manhole shell and deformation of the body

Plastic manholes made of polypropylene (PP) are highly durable, but not indestructible. The most common mechanical failure we encounter in practice is deformation or cracking of the manhole shell. This usually happens when the manhole is not self-supporting and the surrounding backfill was not done correctly – for example, when it was backfilled with unsuitable material (sharp-edged gravel over 30 mm, or unstable soil without compaction in layers of up to 20–30 cm).

Another common scenario: the manhole was installed on an unstable base and over time the entire body shifted off-axis, causing stress at the pipe connection points. The result? Leaks in the collars and gradual flooding of the manhole with groundwater or rainwater. In extreme cases, the pipe collar is torn out of the manhole wall.

Prevention is simple: a properly dimensioned self-supporting manhole, such as the circular PP 1300×1000 plastic self-supporting water meter manhole, can withstand lateral soil pressure without concrete casing, but only if the backfill is done according to the technological specification – with sand or small gravel, in layers, with compaction.

Failures of the lid and cover – a neglected detail with serious consequences

The manhole lid is its first line of defense against surface water, as well as against unauthorized access and mechanical damage. In practice, we most often see these problems:

Deformed or cracked lid – caused by heavy machinery driving over the manhole area without a corresponding load-bearing cover (class D400 for roads, C250 for paved areas)
Leaky lid – surface rainwater enters the manhole, and if there is a water meter or electrical installation of the pumping unit inside, the consequences are serious
Frozen or buried lid – the manhole cannot be opened, which in the case of a failure dramatically prolongs the response time

Solution: the lid must be dimensioned for the expected load, must be mounted in a load-bearing frame with a gasket, and its location must be permanently accessible. If surface water flooding is a risk, install a lid raised at least 50–100 mm above the surrounding terrain.

Corrosion and wear of mechanical components inside the manhole

Inside the pumping manhole, components operate in an extremely aggressive environment. Sewage water contains H₂S (hydrogen sulfide), which attacks metal parts. Screws, clamps, metal consoles, and even some pumps made of low-quality materials begin to rust within 2–3 years. Pumps with motors made of stainless steel (AISI 304 or AISI 316) last significantly longer – but even here it depends on the concentration of aggressive substances.

The check valve is a mechanical component that wears directly in proportion to the intensity of operation. In a pumping manhole with a four-person household, the pump can start 20–40 cycles per day – each cycle loads the valve twice (when the pump is turned on and off). In a year, that is ten thousand cycles. Cheap PVC valves last 2–3 years, while quality ones made of PP or with rubber seals last 5–10 years.

Hydraulic faults – when water doesn’t go where it should

Backflow and its consequences

Backflow is one of the most damaging hydraulic faults. It occurs when wastewater from the public sewer flows back into the household – usually during heavy rain when the sewer is overloaded. If the household has no protection, water finds its way through floor drains, toilets or sinks in the basement.

Protection against backflow is a necessity, not a luxury. Drainage shaft with a backflow valve 400/160 is an elegant solution directly integrated into the inspection shaft – the valve opens only in the direction of discharge and closes mechanically in case of backflow. In practice, however, we see that backflow valves do not function properly for several reasons:

The valve is clogged with solid waste (wet rags, fats, hair) and cannot close completely
Sediment settles under the sealing surface of the valve and prevents it from seating
The valve is installed in the wrong direction (yes, it does happen)
The valve gasket is cracked due to low temperatures or chemicals

Therefore, regular inspection is essential – at least once a year it is recommended to inspect the valve, clean the sediment and check the mobility of the valve flap. For more information on this topic, see the article Backflow protection: when do I need a backflow valve in the shaft? in our Knowledge Centre.

Air pockets in the discharge pipe

This is a sneaky fault because it appears suddenly and without warning – the pump is running, but the performance drops dramatically or the water is not pumped at all. Cause: an air pocket has accumulated in the discharge pipe, blocking the flow.

Air pockets form when:

The discharge pipe does not have sufficient slope or has local bends upwards (so-called siphon effect)
The discharge pipe is too long (over 30–40 m) without an air vent
The pump is sucking in air due to low water level in the shaft (the float switch is set too low)
There is no check valve on the discharge pipe or it is damaged – water flows back into the shaft and when the pump starts again, it "draws in" air

Solution: properly dimension the discharge pipe route with a minimum slope of 1–2 % without local upward bends, install an air vent at the highest point, and set the float switch so that the pump never runs dry.

Overflow and insufficient drainage of flush water

If the shaft "cannot keep up" – that is, it fills faster than the pump can pump out – it can have several causes. The most common: the pump is undersized for the actual inflow. For example: for a four-person household with a shower, washing machine, dishwasher and two toilets, the average inflow of flush water is 2–3 l/s in peak load. A pump with a capacity of 0.8 l/s simply cannot keep up.

Second scenario: the pump is correctly dimensioned, but the discharge pipe is oversized and the flow speed is so low that solid substances settle in it, gradually narrowing the cross-section to a critical level.

Electrical and control faults of pumping units

Float switch – the most common culprit

From practical experience: the float switch is by far the most common cause of electrical faults in pumping units. It is a cheap component on which the entire system function depends, and precisely for this reason many manufacturers of pumping units save on it. Typical failure scenarios:

Jammed float – wet fibers, paper or solid waste wrap around the float cable and prevent it from moving. The pump will not start even if the shaft is full, or on the contrary, it will run continuously even if it is empty (dry running)
Cracked float buoy – water enters the float, it loses buoyancy and "sinks" – the pump runs continuously, overloads and overheats
Corrosion of contacts – in a wet and aggressive environment of the septic tank, electrical contacts inside the switch oxidize, the contact does not close or open reliably
Incorrect float height setting – the switch is set too low, the pump runs too short and too often (so-called cycling), which dramatically shortens the motor life

Solution: regularly visually inspect the float switch and replace it preventively every 2–3 years. A quality replacement switch costs a few euros – much less than repairing a burnt motor. An alternative is pressure sensors or ultrasonic level sensors, which have no moving parts, but are more expensive.

Electrical faults of the pump

The motor of the pump in the pumping unit is submerged in liquid, which is a common design intention – the liquid cools the motor. But when the pump runs dry (which happens when the float fails), the motor overheats and its winding is damaged. The result is typical: the pump does not work at all, or the circuit breaker trips.

Another source of problems are the supply cables of the pump. In the aggressive environment of septic water, cable insulation degrades, especially if a cable not certified for permanently submerged installations is used. A short circuit in the cable is a serious problem – apart from the pump failure, it can also endanger the entire electrical circuit and the safety of people.

Pumping units, such as sewage pumping shaft MIDI 1600×1000 – complete unit, deliver the pump and electrical part as a complete unit ready for installation. It is essential that the electrical connection and the socket for the pump are installed by a qualified professional and that the plug is located at least 1 meter above ground level, in a dry and protected place.

Overload and thermal protection of the pump

Most modern pumps have built-in thermal protection – in case of overheating, the power supply is cut off and the pump stops. If the thermal protection is triggered, the pump will automatically restart after cooling down (usually 15–30 minutes). If this repeats, the cause of overheating must be identified:

Dry running (float switch is not working)
Clogging of the pump with solid waste – increased resistance, the motor is running with higher current
Network voltage is out of tolerance (voltage fluctuation below 200 V or above 240 V)
The pump is undersized for the required head – it is constantly operating at the edge of its performance

Clogging of the pump – practical causes and cleaning procedure

Clogging of the pump is common in practice, especially in households, where wet paper towels, condoms, sanitary napkins or large amounts of solid kitchen waste are flushed into the toilet or sink. Circulation pumps in manholes usually have one impeller with a diameter of 40–80 mm and a free cross-section of 35–50 mm. Anything larger will jam.

Procedure for manual removal of clogging:

Disconnect the pump from the power supply – always the first step, no compromises
Lift the pump out of the manhole using the lifting rope (the lifting rope must always be mounted and must not be removed)
Check and clean the inlet openings and the impeller – best with a high-pressure water jet
Manually rotate the impeller through the service opening and verify that it turns freely
Before returning the pump to the manhole, clean the bottom of the manhole from sediment

In larger pumping chambers with a diameter of 1000 mm, such as the sewage pumping chamber MIDI 1300×1000, there is enough space to work inside the chamber from above. In smaller diameter chambers, access may be limited and sometimes a worker with long arms or a special tool is needed.

Problems with the water meter chamber – specific faults

Frozen water meter and valves in the chamber

The water meter chamber is designed so that the internal temperature does not drop below 0 °C even in the strongest frost. The correct depth of installation is the most important factor – details can be found in the article Chamber burial depth: how to correctly place the chamber below the frost level. However, even a properly buried chamber can have a freezing problem if:

The bottom of the chamber is not sealed and cold air is flowing in from the ground through the pipe collars
The chamber lid is not airtight or is damaged and frost is entering from above
The chamber was installed at an insufficient depth – the minimum depth of the top surface of the pipe below the frost line is usually 1.0–1.2 m (depending on the climatic region of Slovakia)
The chamber was empty for a long time without water flow during strong frosts

If the water meter is frozen, do not try to thaw it with a hot flame – the risk of cracking the water meter body or plastic parts of the chamber is high. Use warm water or an electric heater with a light bulb, slowly and evenly. To protect against future damage, add thermal insulation to the pipes inside the chamber (e.g., PEF pipe insulation) and check the tightness of the lid.

A reliable choice for areas with higher frost risk are full-wall plastic chambers with a larger internal volume – for example, the circular water meter chamber PP 1600×1000 plastic self-supporting – where the larger air cavity inside better dampens external temperature fluctuations than smaller types.

Groundwater penetrating into the chamber

If water appears inside the chamber without an obvious cause, it is either groundwater penetrating through the bottom or walls of the chamber, or surface water penetrating through the lid or pipe collars. It is important to distinguish between these, as the solutions differ.

Groundwater seeps in through the bottom when the groundwater level is high after rain – the sump "floats". This is a serious problem because it lifts the entire sump, and if it is not sufficiently loaded or anchored, it may rise. Preventive measures: concreting the base slab or draining the area around the sump using drainage pipe. More about choosing the right solution is described in our article Plastic sump vs. concrete sump: which is more cost-effective?

Regular sump maintenance – what, how often, and why it is worth it

Most sump and pumping unit failures are operational – they occur due to neglected regular maintenance. The following table summarizes the recommended intervals and tasks:

Interval	Task	What to look for / remove
Monthly	Visual inspection of the float and water level	Stuck float, unusual pump noise
Quarterly	Inspection of the sump area, lid, and connections	Water ingress, corrosion marks, lid displacement
Biannually	Cleaning the sump bottom, checking the check valve	Sediment, valve contamination, float movement
Annually	Full inspection – pump, cable, electrical system	Cable insulation, motor current draw, shaft condition
Every 3–5 years	Preventive replacement of float, valve, and seals	Preventing failure, verifying the functionality of the backup system

From practice we can confirm: households that follow at least a biannual inspection schedule experience dramatically fewer failures. A pumping unit with a single pump and no backup solution is especially vulnerable – if the pump fails at night or over the weekend and the sump fills up, the damage to the basement can exceed the cost of a completely new unit. For critical applications, therefore, we recommend units with two pumps, where the system automatically switches to the second pump in case of failure of the first.

Failures after warranty and the decision to repair or replace

When a failure occurs outside the warranty period, most owners face the question: repair or replace? A few practical criteria:

Age of the equipment: If the pump is older than 10 years, repairing the core (motor, impeller) is usually not economically viable – the cost of spare parts plus labor approaches the price of a new pump
Availability of spare parts: Spare parts for some cheap imported pumps are not available
Type of failure: Worn seal, float switch, or check valve – repair. Burned motor, broken shaft, or damaged impeller – replace
Condition of the sump: If the sump itself is in good condition, replacing just the pump makes sense. If the sump is deformed, leaking, or improperly dimensioned, it may be better to address the entire system at once

It is good to know that modern sumps such as MIDI 1600×1000 complete unit are designed so that the pump can be easily replaced without the need for excavation or special tools – the pump hangs on a guiding system and is pulled up using a lifting rope. This is an important design detail that should be verified when selecting a unit.

Emergency situation recovery – what to do immediately

Sometimes a failure occurs suddenly – the sump overflows, the basement is flooded, or the garden WC container stops working. What to do:

Immediately limit the inflow into the sump – do not discharge more water (do not use the toilet, washing machine, or sink)
Check if the pump is running – listen for the motor sound or check the indicator light
Check the circuit breaker for the corresponding circuit on the electrical panel
If the sump is full and the pump does not start, you can temporarily use a portable sewage pump to manually pump the contents into containers or a higher-level sewer sump
If there is visible damage to the pump or cable, do not touch the pump without being certain that the electrical circuit is disconnected – safety first
Contact a professional service if you are unsure of the cause – most companies offer 24/7 emergency service

Most frequently asked questions (FAQ)

Why is the pump running, but the water is not going out?

The most common cause is an air pocket in the discharge pipe or a clogged pump impeller due to solid waste (wet paper towels, fabrics). Another possible cause is a stuck or non-functional check valve that cannot open the path for water. Procedure: disconnect the pump from the power supply, remove it from the sump, inspect the impeller and clean it. If the impeller is in good condition, check the discharge pipe for air pockets.

The pump turns on and off very quickly – what does it mean?

This is known as "chattering," where the pump performs very short cycles (less than 30 seconds). Causes: the float switch is set to a too small water level difference (the on and off levels are too close), or the water inflow into the sump is equal to the pump capacity and the sump does not have time to empty before the next start. Chattering dramatically shortens the pump's lifespan and must be eliminated by adjusting the float or replacing it with a switch with a larger range.

The check valve works well, but I can smell sewage – what is wrong?

The check valve prevents physical water flow but not the spread of odors. The smell usually comes from unsealed inspection openings, dried-out traps on rarely used fixtures (floor drains in the basement), or leaks in pipe connections. Solution: regularly check and pour water into unused traps, inspect the tightness of the sump inspection opening, and seal all exposed pipe penetrations.

After heavy rain, there is water in the basement despite having a check valve – why?

There are several scenarios: (1) The check valve is dirty and cannot fully close. (2) The water did not come from the sewer but from saturated soil through cracked foundations or around cable and pipe penetrations. (3) The volume of wastewater from the household during the rain is so large that the pumping pump cannot keep up (power outage during the storm is a typical complication – if there is no backup power source like a UPS or generator). We recommend a comprehensive diagnosis: first determine the actual source of the water (dye, probes) and then choose the right solution.

How long does a pump in a pumping sump last?

With proper installation, correct sizing, and regular maintenance, the lifespan of a quality submersible pump is 8–15 years. Cheap pumps from Asian production without a reputable brand usually last 2–4 years – they mostly fail due to bearings or shaft seal damage. For critical applications (a family home without a backup system), we recommend investing in a reputable brand (Grundfos, Pedrollo, Jung, Lowara) and having one spare unit ready in dry storage.

Can I clean the pumping pit myself, or do I need a professional?

Regular maintenance – visual inspection, cleaning the float, checking the check valve – can be done by any resourceful homeowner as long as safety rules are followed (disconnecting from electricity, wearing protective gloves, using a respirator in case of strong odors). Cleaning the bottom of the pit with a sewage pump or manually cleaning the impeller is also not rocket science. What requires a professional: electrical diagnostics and repairs, replacing the pump (unless you are experienced), sealing leaks in the pit casing, and inspecting the discharge pipe with a camera.

Conclusion: Pumping pit issues are solvable if you know where to look

Pits and pumping units are robust devices designed for decades of reliable operation. Most of the faults we encounter in practice have specific and identifiable causes – a jammed float switch, a clogged check valve, an air pocket in the pipe, or a blocked impeller. None of these faults are mysterious or puzzling if you know where to look. The key to trouble-free operation is a combination of proper installation (correct depth, correct sizing, quality components), regular preventive maintenance, and quick response to the first signs of a problem.

If you are considering a new pit or pumping unit and want to avoid common mistakes, we also recommend reading other articles in our Knowledge Center: How to choose a pit: water meter pit, inspection pit or pumping pit?, Installation of a pumping sewer pit: what you need to know before installation, or Pit for a drilled well: what it must meet and how to connect it to the water supply. The right choice and installation from the start will save you costs and nerves for decades of operation.

Do you have a question about this topic?

Struggling to decide or dealing with a specific situation in your home? Write to us – we are happy to help.