Error keeps returning after drain clearing: sagging pipe trapping sludge
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 drain pan and trap were not the problem here. A sag in the drain line was.
By Team Snowflake | Reviewed 24 Mar 2026
Case summary
Daikin Wall-mounted5 years oldHDBToa Payoh, Singapore
- Concern
- The owner worried that the drain pan had cracked and the whole indoor unit would need replacing.
- Previous advice
- Previous contractor cleared the drain once but the error returned within weeks
- 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
We explained that 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.
Related reading
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