Guides / Faults
Diagnose common condensate pump and AC leak problems, and fix them fast.
Condensate pump not working? Check power, float switch, blockages and alarm faults with this simple guide.
Why your condensate pump is noisy — gurgling, rattling or humming — and how to quieten it.
Condensate pump overflowing? Find the cause — blockages, excess lift or a failed pump — and stop the leak.
Condensate pump running all the time? Check the float switch, non-return valve and pipe for the cause.
Water leaking from your condensate pump? Common causes and simple fixes.
Pump runs but won't pump water? Check for airlocks, blockages and excessive lift.
Condensate pump short-cycling? Why it switches on and off repeatedly and how to fix it.
Air conditioner leaking water indoors? Causes include blocked drains, failed condensate pumps and poor installation.
Condensate Pump Safety Switch: common causes, quick checks and when to replace the pump.
Condensate Pump Line Freezing: common causes, quick checks and when to replace the pump.
Water around an indoor air-conditioning unit does not automatically prove that the pump motor has failed. A dirty tray, blocked inlet, stuck float, loose hose, kinked discharge pipe or frozen external section can create very similar symptoms. Diagnosis should therefore follow the water path in order, beginning at the indoor unit and ending at the discharge point. Isolate the equipment first, contain any water, and avoid repeatedly running an air conditioner that is leaking. A careful check often separates a simple maintenance issue from a pump that genuinely needs replacement. This collection approaches finding the cause of an air-conditioning condensate problem before deciding whether adjustment, cleaning or replacement is appropriate from several practical angles. Start with the guide closest to the equipment or symptom in front of you, then use the linked supporting topics to confirm the details that affect your decision.
The SK-18AE and SK-18CE are both for air-conditioning condensate. Their different body formats, stated application limits and alarm provision mean that one may suit a particular job better than the other; neither should be treated as automatically universal.
A condensate pump that won't work usually has no power, a stuck float switch, a blocked inlet or a failed motor. The full guide explains the checks behind that answer and links the topic to pump choice, safe installation and future maintenance where relevant.
Noise usually comes from vibration against a wall, air being drawn in, debris in the impeller or a worn motor. The full guide explains the checks behind that answer and links the topic to pump choice, safe installation and future maintenance where relevant.
An overflowing pump can't clear water as fast as it arrives, usually because of a blockage, too much lift or a failed motor. The full guide explains the checks behind that answer and links the topic to pump choice, safe installation and future maintenance where relevant.
A pump that never stops usually has a stuck float, water flowing back from the pipe, or can't reach the drain. The full guide explains the checks behind that answer and links the topic to pump choice, safe installation and future maintenance where relevant.
Leaks usually come from loose hose connections, a cracked reservoir or overflow from a blockage. The full guide explains the checks behind that answer and links the topic to pump choice, safe installation and future maintenance where relevant.
If the motor runs but water doesn't move, the cause is usually an airlock, a blocked pipe or too much lift. The full guide explains the checks behind that answer and links the topic to pump choice, safe installation and future maintenance where relevant.
Rapid on-off cycling is usually caused by water draining back into the reservoir or a float set too sensitively. The full guide explains the checks behind that answer and links the topic to pump choice, safe installation and future maintenance where relevant.
An indoor AC leaks water when condensate can't drain away — usually a blocked drain, failed condensate pump, poor drain fall, or a dirty filter causing icing. The full guide explains the checks behind that answer and links the topic to pump choice, safe installation and future maintenance where relevant.
Begin by identifying the equipment precisely. Record the indoor-unit or appliance model, its rated output, the position of the drain and any existing pump model. Describe the symptom or the reason a pump is required. Then measure the route: inlet fall, vertical rise, horizontal length, bends and final discharge point. These facts are more useful than choosing from a product picture or a familiar brand name.
Read the relevant guide once for the overall approach and again while checking the installation. Separate confirmed facts from assumptions. If the work involves mains wiring, concealed leaks, boiler components or an unclear safety circuit, stop and involve the appropriate competent professional. The purpose of these pages is to make that conversation better informed, not to encourage unsafe work.
Condensate begins in the indoor unit, passes through a tray and drain outlet, reaches a reservoir by gravity and is then pushed through a small discharge tube. Every stage must remain clear. A pump cannot compensate for an inlet that runs uphill, a tray filled with debris or a blocked final drain. Likewise, a clean reservoir does not solve an outlet pipe that is kinked or routed beyond the pump’s usable lift.
Thinking of the installation as one route also improves fault finding. Follow the water in order and test the complete cycle after any work. This avoids replacing a pump unnecessarily and reduces the chance that a new unit inherits the old fault. Where overflow protection is required, prove the warning and approved shutdown response as part of that same test.
The SK-18AE costs £59.99 and is the wall-mounted option for air-conditioning systems up to 7.5 kW, with an 18 L/h flow figure, 8 m maximum head and noise rated at 18 dB(A) or less. The SK-18CE costs £69.99 and is the corner option for systems up to 8 kW, with a 10 m maximum head, noise rated at 18 dB(A) or less and a confirmed built-in audible overflow warning.
Use those figures as selection boundaries, not promises that ignore the route. Pipe resistance, fittings, access and mounting quality affect the result. For a simple high-wall split, the SK-18AE may be the clearer fit. For a corner position, longer lift requirement or installation where an audible warning is valuable, consider the SK-18CE. Both have a 2-year warranty.
Isolate electrical equipment before opening covers or working around water. New fixed wiring should be completed by a competent person, and both the pump and air-conditioner instructions must be followed. Mount the pump securely and level, preserve gravity fall into the inlet, support the discharge pipe and avoid dips or tight bends. Keep the reservoir and connections accessible for future cleaning.
Test by introducing clean water at the indoor unit and observing the entire route. Confirm that the pump starts and stops correctly, every joint remains dry and water does not return when pumping stops. If the selected pump provides an alarm, test it deliberately and confirm any approved connection to the air conditioner responds as intended. Commissioning should prove drainage, not merely power.
Inspect the tray, inlet, reservoir, float area, outlet tube and discharge point on a schedule appropriate to the environment. Dusty spaces and heavily used cooling systems may need more frequent attention. Clean only in accordance with the equipment instructions and keep liquid away from electrical parts. After reassembly, repeat the controlled water test and listen for a normal short operating cycle.
Changes in sound, frequent starts, slow clearing, smells or moisture marks deserve early investigation. They may indicate contamination, air entering the line, a restricted pipe or a loose mounting rather than immediate motor failure. Prompt attention is usually easier than dealing with an overflow. Keep a basic service record so a recurring pattern can be recognised.
A pump may merit replacement when its motor has failed, the housing or connections are damaged, the float remains unreliable after proper cleaning, or the existing unit cannot meet the measured route. Diagnose first, because a blocked drain or poor pipe layout can make a healthy pump appear defective. Correct the cause before connecting the replacement.
Use the dedicated air-conditioning condensate pump replacement guide to collect the required measurements and compare both products. Orders placed before 1pm on a working day are offered with £8.99 next-working-day UK delivery, but compatibility and safe fitting remain more important than speed.
Use the page list above as a working reference rather than reading titles in isolation. Open the closest match, note the quick answer, and compare its detailed checks with the real installation. Follow related links when the question crosses into another area such as wiring, noise, lift, cleaning or compatibility. The A–Z index also connects different search phrases to the most relevant full guide.
If a guide confirms that one of the two pumps fits, return to the home-page comparison before adding it to the basket. If the measurements remain uncertain or the work is outside your competence, pause the purchase and ask an air-conditioning professional. A correctly specified, accessible and tested pump is the objective; simply fitting the first available unit is not.
