RO Running Continuously and Not Switching Off (Delhi, 2026)

Do this first: switch it off, then run four free checks

Before anything else, stop the machine. Switch the RO off at the wall socket and close the inlet tap that feeds it. That does two things at once: it stops the pump wearing itself out, and it stops water running to the drain and to your bill for however many days it takes to get someone out. You can switch it back on for a few minutes at a time to run the checks below.

• 1. Is the tank actually full? Lift or rock the storage tank. A full tank is noticeably heavy; an empty one is surprisingly light. If it is genuinely empty and the machine is running, the machine is doing its job and the real problem is that it cannot fill — see RO not filling the tank. If it is heavy and the machine is still running, you are in the right place.
• 2. Is the drain line running? Find the thin tube that goes to the sink waste and listen or feel it. Water moving through it while the tank is full and nobody is drawing water is the clearest sign the machine has not received its stop signal.
• 3. Open the RO tap and see what comes out. A full tank should give a strong, steady stream that runs for a while. A weak dribble from a tank that feels full is a specific and very common clue — it points at the tank itself, and section three below is yours.
• 4. Check the pressure of the water going in. Open the tap or line feeding the RO into a bucket. Is it a strong flow or a tired one, and is it different at different times of day? On upper floors and during weak-supply hours the answer is often the whole story.

Those four observations narrow it to one of the four causes below, and they cost nothing.

The stop signal never arrives: high-pressure switch or float valve

This is the most common cause by a distance. Something has to tell the machine the tank is full, and if that part fails the machine has no way of knowing when to quit.

• The high-pressure switch (on pumped systems). As the tank fills, pressure builds in the line, and at a set point a small switch opens and cuts the pump. If the switch has failed, or its contacts have stuck closed, or its little tube has clogged with scale so it never sees the pressure, the pump simply never gets told to stop. How it looks: the tank is genuinely full, the tap gives a strong stream, and yet the pump hums on and the drain keeps running.
• The float valve (on gravity-fed and open-tank systems). A float rises with the water level and mechanically shuts the inlet at the top. Floats stick on their guide, get furred up with scale in hard NCR water, or come off their arm. How it looks: the tank overflows, or water keeps arriving at a tank that is clearly at the top.
• The solenoid shut-off valve. Many units use an electrically operated valve to close the inlet when the machine is told to stop. If it jams open, or if it never receives the signal because the switch above has failed, water keeps flowing regardless. How it looks: indistinguishable from the switch fault at your end — a technician tells them apart at the unit.

Is it DIY? No. These are small, inexpensive parts, but they sit inside a pressurised, powered assembly and diagnosing which of the three has failed needs the machine opened and tested. The good news is that this whole family of faults is at the cheap end of RO repair — it is a component swap, not a new machine, and certainly not a membrane.

A tank that has lost its air charge, so it never builds pressure

This one confuses people, because the tank feels full and yet barely any water comes out. It is worth understanding, because the symptom is so distinctive that it is almost self-diagnosing.

An RO storage tank is not a plain bucket. Inside it there is a flexible bladder holding the treated water, and around that bladder there is a pocket of air under pressure. That air is what pushes the water out to your tap when you open it, and it is also what makes pressure build in the system as the tank fills — which is exactly what the high-pressure switch is waiting to feel. Over years, that air charge can leak away through the valve on the tank.

• What it looks like. The tank is heavy, so you assume it is full, but the tap gives a thin stream that dies quickly. Meanwhile the machine keeps running, because with no air behind the bladder the pressure never rises to the cut-off point, so the switch never trips.
• How to confirm it. The combination is the tell: a heavy tank, a weak and short-lived stream at the tap, and a pump that will not stop. A technician confirms it by measuring the air pressure at the tank valve with the tank drained.
• Is it DIY? No. A storage tank is a pressure vessel. Re-charging one to the wrong pressure, or with the water side not properly drained first, can rupture the bladder and can be genuinely dangerous. Leave it to a technician with a gauge, full stop.
• What it usually needs. Either a re-charge of the air side, or a new tank if the bladder itself has failed. Both are ordinary jobs.

Low inlet pressure, and a check valve letting water back

The last two causes both stop the system ever reaching the pressure at which it would switch off, but for opposite reasons — one is not enough pressure coming in, the other is pressure escaping backwards.

• Inlet pressure too low to reach cut-off. The system needs a certain pressure at the inlet before it can build enough pressure downstream to trip the cut-off. If the supply is weak — a high floor on a tired building pump, a low-pressure hour on the municipal line, a half-open or partly blocked feed tap, a kinked inlet tube, or a choked sediment filter strangling the flow — the machine may run for hours and never get there. How to confirm: the behaviour changes with the time of day, or it started when the building pump or the supply schedule changed, or it began right when the filters became due. Our low water pressure guide covers the supply side, and pressure at a single tap covers the case where only the RO feed is weak. Fix: often a choked filter or a feed tap, sometimes a booster pump — but get it confirmed before buying one.
• A leaking check valve or non-return valve. A check valve sits after the membrane and is supposed to stop treated water flowing backwards. When its seal fails, water leaks back through it instead of holding pressure, so the tank pressure never builds and the machine recirculates endlessly. How it looks: continuous running with a continuous drain flow, and often a tank that fills very slowly or never quite fills. It is another small part, and a technician identifies it by isolating sections of the machine.

Both are worth ruling out before anyone talks about a pump or a membrane, because both are cheaper and both are more common than either.

What it costs you to leave it, when to call, and what to say

Do not live with this one. A continuously running RO has three running costs even before the repair: the pump is designed to run in short bursts and wears out fast when it never stops; water goes to the drain the entire time it runs, which in a city that rations supply is not a small thing; and the pump draws power around the clock, which shows up on the bill. A part that would have been a modest component swap turns into a pump replacement if it is left long enough. Switch it off at the socket, close the inlet, and book the visit.

Call a technician when: the tank is genuinely full and the pump still runs; the tap gives a weak, short stream from a heavy tank; the drain line runs continuously with nobody drawing water; the tank overflows; or the machine has been running non-stop for more than a day.

What to tell them, so they arrive with the right part: whether the tank feels full or empty; what the tap stream is like from a full tank; whether the drain is running with the tap closed; whether the behaviour changes with the time of day; whether the supply, the building pump or the filters changed recently; the age of the unit and of the tank; and whether you have already switched it off at the socket. Mention any leak, new noise or alarm on the same call, since they often share a cause, and say so too if the water has turned cloudy or started tasting bitter or salty — a machine that recirculates endlessly often does both.

Not a DIY job, without exception: the storage tank, which is a pressure vessel; the pump and its wiring; the high-pressure switch and the solenoid; and any pressurised housing. If the machine has stopped doing anything at all rather than refusing to stop, start at RO not working instead.

For the ranges that let you judge the quote, see RO repair cost in Delhi and RO service cost and TDS; if a membrane is proposed as part of the work, membrane replacement cost is the page for that, and ask why a membrane is the answer to a machine that will not switch off. Household habits that keep water use down are in our water supply and tank tips and RO and drinking water tips.