How to Bleed Underfloor Heating Loops for Better Performance
If your underfloor heating system isn’t heating evenly—or not at all—there’s a good chance air is trapped in the loops. Bleeding your underfloor heating is essential for maintaining system efficiency, preventing cold spots, and ensuring consistent comfort.
In this step-by-step guide, we explain when, why, and how to bleed underfloor heating loops safely and effectively.
Why Bleed Underfloor Heating Loops?
Just like traditional radiators, underfloor heating systems can develop airlocks—bubbles of air that block the flow of warm water. These air pockets reduce heat output and can cause parts of the floor to stay cold, even when the system is on.
Signs you need to bleed your underfloor heating:
- Uneven floor temperature
- One or more zones not heating
- Noisy or gurgling pipes
- Recently drained/refilled system
When Should You Bleed Underfloor Heating?
- After initial installation
- Following maintenance or repairs
- If performance drops or zones stop heating properly
Even well-installed systems can trap air over time, so periodic checks are recommended, especially before winter.
Tools You’ll Need
- UFH manifold with isolation valves
- Adjustable spanner or wrench
- Drain hose (optional but helpful)
- Towels or bucket for water spills
Always ensure the system is turned off and cooled down before starting.
How to Bleed Underfloor Heating Loops (Step-by-Step)
Step 1: Switch Off the System
Turn off your boiler or heat source and let the system cool. You don’t want hot water circulating while you work.
Step 2: Locate the Manifold
Your manifold distributes hot water to the individual loops. It will have flow meters, return valves, and air bleed valves.
Step 3: Isolate All Loops Except One
Close off all loops using the return manifold valves, leaving one loop open to be bled at a time.
Step 4: Open the Flow and Return Valves for That Loop
This will allow water to enter the loop and push trapped air toward the bleed point.
Step 5: Open the Air Bleed Valve Slowly
Using a spanner, gently loosen the bleed screw. Air will hiss out, followed by water.
Step 6: Let Water Flow Until It Runs Smooth
Once a steady stream of water (no bubbles) flows, you can close the bleed valve.
Step 7: Repeat for Each Loop
Work through each loop individually, following the same process.
Step 8: Re-pressurise the System
After bleeding, check the boiler pressure and top up the system if needed (typically 1.0–1.5 bar).
Step 9: Restart the System and Test
Turn the heating back on and check that all zones are heating evenly.
Tips to Prevent Airlocks in Future
- Have your installer fit automatic air vents on the manifold
- Don’t drain/refill the system unless necessary
- Use inhibitor fluid to protect against corrosion and microbubbles
- Run your system regularly, even in warmer months, to maintain flow
FAQs
Q: How often should I bleed my underfloor heating?
A: Only as needed—usually after installation, repair, or when performance issues arise.
Q: Can I bleed the system myself?
A: Yes, if you’re comfortable with plumbing basics. Otherwise, contact a professional.
Q: What happens if I don’t bleed the system?
A: Airlocks reduce efficiency and can lead to cold spots, especially in large areas.
Not getting the warmth you expected from your underfloor heating?
Our certified engineers at Interior Screed Ltd can diagnose and resolve system issues quickly—whether it’s trapped air, uneven flow, or a faulty valve.
Get in touch today to book a service visit or preventative maintenance check.
