Error returns after drain clearing: sagging pipe traps mud

The A3 error came back within weeks of every drain clearing. When a fix keeps failing, the real blockage is rarely where the last person cleaned. The problem was not the drain pan or trap, but a sag in the drain line.

By Team Snowflake | Updated 28 Jul 2026

Case summary

Daikin Wall-mounted3-7 years oldHDBToa Payoh, Singapore

Concern: A cracked drain pan was the fear, and with it a whole indoor unit to replace.
Found: Drain line sag inside false ceiling collecting sludge
Key check: Water dye test showed drainage stalling at a low point in the ceiling void
Result: We rerouted the drain line with a steady fall from the indoor unit to the external discharge point. With the dip gone, the A3 error cleared and has not returned.

What we were told

The aircon keeps showing an error and leaking. Someone cleared the drain a few weeks ago and it held for a while, but the same thing is back. This is the second time it has happened, and the owner did not want to keep paying for the same job.

What we checked

The repeat pattern told us the previous clearing had not reached the real blockage. If the pan or trap were the cause, one clearing would have held. We traced the full drain path from the unit to the discharge point.

The A3 error was active on the Daikin indoor unit display.
The drain pan was clean, with no sludge at the outlet. The pan was not holding water.
The drain trap was clear and flowed freely when tested with water, so the early run of pipe was fine.
A water dye test showed drainage stalling at a low point inside the ceiling void, where the drain line had sagged.
The sag held a thick plug of sludge and biofilm that choked the flow.

What we found

The drain line dipped inside the false ceiling. That low point worked as a trap, where sludge and biofilm settled and built up over time. Each clearing flushed it out, but the dip refilled within weeks because water naturally pooled there. The Daikin A3 error triggers when the drain level control senses backed-up water in the pan. That happened every time the sag blocked again, which is why the same fix never lasted.

What fixed it

Flushing the drain again would only buy a few more weeks. The fault was the routing itself, not the buildup. We recommended rerouting the drain line through the ceiling void so it falls steadily with no dips. With no low point, sludge has nowhere to settle and the flow stays clear. The work meant opening a small section of the false ceiling to reposition the pipe.

Outcome

We rerouted the drain line with a steady fall from the indoor unit to the external discharge point. With the dip gone, the A3 error cleared and has not returned.

What this case teaches us

A drain error that keeps returning points to the pipe, not the pan

A clearing that works for a few weeks then fails means the blockage is reforming somewhere upstream of where it was cleared.
A sag in the drain line acts as a permanent trap. Flushing empties it, but water pools back at the dip and sludge rebuilds.
Fixing the routing so the pipe falls steadily costs more than another flush, but it ends the cycle instead of resetting it.

Questions this case answers

Why does the Daikin A3 error keep coming back after the drain is cleared?

Because the clearing has not reached the spot where sludge rebuilds. In this Toa Payoh flat the pan and the trap were both clean and flowed freely. A dye test then showed water stalling at a dip in the drain line inside the ceiling void, and that dip held a thick plug. Flushing empties it, water pools back, the plug reforms.

Aircon leaking again a few weeks after a drain flush: what is going on?

A fix that holds for a short stretch then fails is telling you the blockage is reforming, not that it was missed. Water finds any low point in the pipe and sits there. Sludge and biofilm settle in that standing water and choke the flow again. The trap is paying for the same flush on repeat instead of correcting the fall of the pipe.

Does a returning drain error mean the drain pan has cracked?

Rarely. On this Daikin the pan was clean, held no water and showed no damage at the outlet. A3 fires when the drain level control senses water backing up, and backed-up water can start anywhere downstream of the pan. We check the pan, then the trap, then the full pipe route before anyone talks about replacing an indoor unit.

How do I know if the drain pipe is sagging inside the false ceiling?

A dye test through the line will show it. Coloured water travels freely along a pipe with steady fall and stalls at a dip. That is what pinned the fault here, at a low point in the ceiling void. Rerouting the pipe so it falls steadily costs more than another flush, and it ends the cycle rather than restarting it.

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