RO not filling the tank: pump, membrane or something simpler

An empty tank has a short list of causes. Start with the ones that cost nothing to check.

Is water reaching it?

The inlet valve on the supply line — is it open? Has the overhead tank run dry? Is there pressure at the kitchen tap? A surprising number of 'RO broken' calls are a closed inlet after someone cleaned behind the unit.

Is the unit getting power?

Check the plug and the socket. Many ROs are plugged into a socket shared with something else that gets switched off.

Humming but no water

The pump is running and pushing against something. Usually a blocked sediment or carbon pre-filter — if they are overdue, this is the likely cause. Sometimes a blocked membrane, if the pre-filters were skipped for a long time.

Silent with power

The pump has failed, or the low-pressure switch has cut it off because there is no inlet water, or the high-pressure switch thinks the tank is full. A technician tests each in a couple of minutes.

Fills very slowly

Membrane wearing, or inlet pressure low. Not a fault yet; a warning.

If the unit hums continuously without producing water, switch it off. A pump running dead-headed against a blockage overheats and fails, turning a filter change into a pump replacement.

What the visit checks

Inlet pressure, then each pre-filter, then the pump's output pressure, then the membrane. The fault is found in order, and only the failed part is replaced.