Weil-McLain A28 Error — What It Means
Weil-McLain boiler manuals do not list an A28 error code. The display may actually show E28, which indicates a condensate drainage problem. The boiler has detected that condensate water is not leaving the unit properly, usually because the trap or drain line is blocked, frozen, or improperly routed.
If your display truly reads A28 and not E28, consult your specific model manual or the control module documentation, because fault codes vary by series (Ultra, AquaBalance, CGa, etc.). For the verified E28 condensate fault, the boiler will lock out until the drainage path is cleared and the water can flow freely again.
Before You Replace Anything
Homeowners sometimes replace the control board or call for a full heat-exchanger flush when the real problem is a $5 condensate trap full of sludge. Inspect and clean the trap and drain line first.
Common Causes
- Frozen condensate drain line (~40%) In cold weather the outdoor termination or an uninsulated section of drain tubing freezes and blocks water from leaving the boiler.
- Sludge or debris in condensate trap (~35%) The trap fills with scale, dirt, or biological buildup and stops water from flowing through.
- Improper drain routing or slope (~15%) The condensate line was installed with insufficient downward pitch, a long horizontal run, or a loop that traps water.
- Kinked or damaged drain tubing (~10%) The plastic condensate hose is pinched, crushed, or has a hole that prevents proper drainage.
Quick Diagnosis
Answer these to narrow it down fast.
Is the outdoor drain termination iced over or covered in snow?
No: Move to the next check.
Can you remove the condensate trap and see standing water or sludge inside?
No: Check the entire drain path for kinks, improper slope, or a blockage farther downstream.
Does the boiler clear the fault after you clean the trap and restore drainage?
No: The issue may be a failed condensate sensor, improper venting, or an internal drainage problem. Call a technician for diagnostics.
Step-by-Step Fix
- Turn off power to the boiler at the service switch or circuit breaker and let the unit cool.
- Locate the condensate trap at the outlet of the heat exchanger (check your model manual for the exact position).
- Remove the trap by loosening the fittings or clips and pulling it free. Have a bucket or towels ready for water.
- Clean the trap and drain tubing with water and a bottle brush to remove sludge, scale, and debris.
- Inspect the entire drain path from trap to termination. Thaw any frozen sections and straighten kinked tubing.
- Reinstall the trap with fresh seals or O-rings if they are worn. make sure all connections are snug and leak-free.
- Restore power and monitor the display. The fault should clear once water flows freely and the boiler completes a drain test cycle.
Parts Often Needed
| Part | Notes |
|---|---|
| Weil-McLain condensate trap | Amazon | Model-specific. Order by your boiler series (Ultra, AquaBalance, etc.) from a heating supply house or authorized dealer. |
| Condensate drain tubing (PVC or flexible) | Amazon | Use 3/4-inch or 1-inch as specified in your installation manual. Buy a few extra feet for routing repairs. |
When to Call a Pro
Call a qualified heating technician if the fault returns after you clean the trap and drain line, if you cannot locate or access the condensate system, if the boiler shows other error codes in the history menu, or if you suspect a control-board or sensor failure. A pro can run full diagnostics, check vent and condensate routing against code, and order the correct model-specific parts from Weil-McLain. Gas appliances require proper venting and combustion-air setup, so any recurring lockout or installation issue should be handled by a licensed contractor.
Rough cost: DIY runs about $10-30 in parts (new trap or tubing), 30-60 min. A pro service call runs about $150-250 for a service call and condensate system cleaning.