Error Keeps Returning After Drain Clearing: Sagging Pipe Trapping Sludge

• •Concern: Worry was that the drain pan had cracked and the entire indoor unit needed replacing.
• •Previous advice: Previous contractor cleared the drain once but the error returned within weeks
• •Key check: Water dye test showed drainage stalling at a low point in the ceiling void

The repeat pattern after drain clearing suggested the blockage source was not at the drain pan or trap. We traced the full drain path.

• •A3 error was active on the Daikin indoor unit display.
• •Drain pan was clean. No sludge buildup at the outlet.
• •Drain trap was clear and flowing when tested with water.
• •Water dye test revealed drainage stalling at a low point inside the ceiling void where the drain line had sagged.
• •The sag had collected a thick plug of sludge and biofilm that restricted flow.

The drain line had a sag, a dip in its routing inside the false ceiling. This low point acted as a trap where condensate sludge and biofilm accumulated over time. Each drain clearing flushed the sludge out temporarily, but the sag refilled within weeks because water naturally pooled there. The Daikin A3 error triggers when the drain level control detects backed-up water in the pan, which happened every time the sag re-blocked.

We explained that flushing the drain again would only buy a few more weeks. The root cause was the drain line routing itself. We recommended rerouting the drain line through the ceiling void to maintain a consistent downward gradient with no dips. This would prevent sludge from accumulating at a low point. The rerouting required opening a small section of the false ceiling to reposition the pipe.

The drain line was rerouted with a consistent fall from the indoor unit to the external discharge point, the A3 error cleared and has not returned.

Why drain line routing matters as much as drain clearing.

• •A drain line sag creates a low point where sludge accumulates faster than normal flow can clear.
• •Flushing the drain fixes the symptom temporarily, but the sag refills within weeks.
• •Rerouting the line to maintain consistent downward fall eliminates the recurring blockage at the source.