To purge a hydronic heating system under the floor, locate the bleed valves, open them, and allow trapped air to escape until water flows steadily.
Purging air from hydronic floor heating systems is essential for maintaining efficiency and preventing damage. Air pockets reduce heat transfer and can cause noisy operation. This guide covers professional techniques for complete system purging.
Why Purging Hydronic Systems Matters
Air in hydronic systems causes several problems:
- Reduced heat output from floor loops
- Gurgling noises in pipes
- Increased strain on circulator pumps
- Potential corrosion from oxygen exposure
Tools Needed for Purging
| Tool | Purpose |
|---|---|
| Washing machine hose | Connects to drain valves |
| 5-gallon bucket | Collects purged water |
| Adjustable wrench | Valve operation |
| Pressure gauge | Monitors system pressure |
Step-by-Step Purging Process
1. Prepare the System
Shut down the boiler and allow it to cool completely. Hot systems risk thermal shock when introducing fresh water. Check that your check valves are functioning properly.
2. Identify Key Components
Locate these critical parts:
- Boiler drain valves (typically blue handles)
- Zone valves or circulator pumps
- Expansion tank connection
- Make-up water supply
3. Connect Drain Hose
Attach a washing machine hose to the lowest drain valve in the system. Run the other end to a floor drain or bucket. Open the valve slightly to begin water flow.
4. Start Purging Sequence
- Close the return line ball valve
- Open the supply side zone valve manually
- Slowly open the drain valve fully
- Activate the circulator pump
5. Monitor Water Flow
Watch the discharge water for air bubbles. According to Radiant Professionals Alliance, you should flush until achieving a steady, bubble-free stream for at least 2 minutes per zone.
6. Restore System Pressure
After purging, close the drain valve and reopen the return line valve. Use the system fill valve to restore pressure to 12-15 psi.
Advanced Purging Techniques
Using Air Separators
Many systems include automatic air separators. These devices collect air bubbles at high points in the system. During purging, ensure the air vent is open to release trapped air.
Zone Isolation Purging
For multi-zone systems, install isolation valves to purge one zone at a time. This ensures complete air removal from each circuit.
Chemical Flushing
For older systems, consider adding a cleaning solution before purging to remove sludge. The ACHR News recommends professional-grade cleaners for best results.
Maintaining a Purged System
After successful purging:
- Check pressure weekly for the first month
- Listen for unusual pump noises
- Monitor heat output across all zones
- Consider installing an automatic air vent
When to Call a Professional
Seek professional help if you encounter:
- Persistent air locks after multiple purges
- Significant pressure drops between purges
- Evidence of leaks in floor loops
- Corrosion in system components
