The drain line heater is a heating wire wrapped on the freezer drain line to keep meltwater from refreezing on its way out. When it fails, ice plugs the drain, water backs up into the pan or floods the box, and ice builds on the floor. A technician tests and replaces the heater.
A defrost cycle turns frost into water, and that water has to leave the box without freezing. The drain line runs through very cold air, so it depends on its heater to do its job.
What it does
A self-regulating or fixed-wattage heater cable is wrapped along the drain line and sometimes into the drain pan. It runs during defrost or continuously depending on the system. The heater keeps water flowing to the outside drain or a floor drain, and the line is sloped and insulated so water does not sit.
Signs it is failing
- Water on the floor near the evaporator.
- Ice forming at the drain outlet or in the pan.
- Drain pan overflowing after defrost.
- Ice ridge on the floor near the coil.
- Heater cable cold when it should be warm.
- Repeated freeze-ups of the drain.
Common causes of failure
| Cause | What happens |
|---|---|
| Burnt or broken cable | No heat along the line |
| Power loss to the heater | Blown fuse or failed relay |
| Poor insulation | Heat escapes and water refreezes |
| Wrong slope or sag | Water pools and freezes |
| Debris in the line | Blockage even with heat |
What you can safely check
- Look for ice. Where does it begin on the drain line?
- Note the timing. Does it happen after defrost?
- Clear loose debris. From the pan, not the line.
- Do not pour hot water. It can refreeze further down the line.
This part is on live power or connected to the pressurized refrigerant circuit. Do not open the electrical box, bridge terminals or loosen fittings. Only a qualified technician should test or replace it.
What a technician does
- Tests the cable for continuity and insulation resistance.
- Checks the power supply and controls.
- Clears ice and flushes the line.
- Replaces heater cable and insulation.
- Corrects slope and traps if needed.
Keeping it healthy
- Flush the drain line as part of maintenance.
- Keep insulation intact and dry.
- Report ice at the outlet promptly.
- Check the heater at yearly service.
A blocked drain can flood a freezer floor overnight, and the ice that results is a slip hazard for staff. Prevention is simple by comparison.
When to call for service
Call if water is leaking inside the box, ice is building on the floor or the drain pan is overflowing. Keep the area dry and mark any ice as a slip hazard while you wait for repair.
Repair or replace
Heater cables are replaced, and the line is re-insulated and sealed. If the line is sagging or badly sloped, that is corrected too. See how to flush a drain line and water leaking inside.
Related reading: the parts and components guide, ice on the floor or ceiling and defrost heaters.
Questions about this part
Do coolers need a drain heater?
Usually only when the drain passes through freezing space.
Can I use hot water to clear it?
It may refreeze downstream. Ask a technician.
Why does the pan overflow?
A blocked or frozen drain. The heater or the line needs attention.