If you’ve just had your central heating system refilled in Bordon and noticed some radiators staying cold at the top, you’re likely dealing with trapped air. This common issue can cause uneven heating, higher energy bills and noisy pipes. In this guide, we’ll explain what’s happening, show you how to bleed radiators safely and share expert tips to prevent it from happening again.
Understanding Why Radiators Go Cold After System Refill
When your heating engineer refills the system—perhaps after a repair or a power flush—air can become trapped in the pipework or radiator bodies. Unlike water, air rises within radiators and collects at the top, blocking hot water from circulating properly. The result is a chilly radiator head and a warm base.
Signs of Trapped Air in Your Radiators
- Partial warmth: Radiators that are hot at the bottom but cold at the top.
- Gurgling or rumbling noises when the heating runs.
- Uneven temperatures across your radiator network.
- Pressure drops on your boiler’s gauge after refilling.
Step-by-Step Guide to Bleeding Your Radiators
Bleeding a radiator is a simple DIY task that can restore even heat distribution. Follow these steps carefully:
- Switch off the boiler and allow radiators to cool. Working on a cold system prevents hot water burns.
- Place a cloth or small container under the bleed valve (usually on the side or top corner of the radiator).
- Insert a radiator key or flat-head screwdriver into the bleed valve.
- Turn the valve counter-clockwise slowly. You’ll hear a hiss as air escapes.
- When water starts to drip steadily, close the valve by turning it clockwise.
- Check the boiler pressure gauge; if it’s dropped below the recommended level (typically 1–1.5 bar), use the filling loop to top up. Always follow your boiler manual.
Checking System Pressure and Other Considerations
After bleeding, maintaining correct pressure is vital:
- Locate the pressure gauge on your boiler. If it’s below 1 bar, increase pressure slowly via the filling loop.
- A sudden refill can introduce more air—bleed again if you notice any hissing.
- If pressure drops frequently, you might have a leak or faulty component that needs professional attention.
When to Call a Professional Gas Safe Engineer
If bleeding and basic checks don’t solve the problem, it’s time to call a Gas Safe engineer. In nearby villages like Alton, Liphook and Petersfield, our experts can quickly diagnose and fix complex issues:
- Persistent airlocks that need a thorough system flush.
- Radiator valves or pump failures causing uneven heat.
- Boiler faults triggering repeated pressure loss or noisy operation.
For major updates or if you’re thinking about a new boiler installation, our team in Farnham and Whitehill can help you choose the right high-efficiency model and complete the work safely.
Regular boiler servicing reduces the risk of airlocks and breakdowns, and adding inhibitor chemicals during a service prevents sludge and corrosion.
To avoid unexpected repair bills, consider our comprehensive boiler cover plans—perfect for homeowners in the GU35 area and beyond.
Preventing Future Problems
Proactive maintenance keeps your radiators and boiler running smoothly:
- Annual boiler servicing by a qualified engineer.
- Power flushing your system every 4–6 years to remove sludge.
- Top up inhibitor levels annually when bleeding radiators.
- Monitor your system pressure monthly and bleed any radiators showing airlocks.
Frequently Asked Questions
Why do I get air in my system after a refill?
Refilling allows fresh air into the pipes and radiators. Bleeding releases this trapped air, restoring proper water flow.
Can I leave my boiler off while bleeding radiators?
Yes. Always switch off and let everything cool to avoid hot water burns.
How often should I bleed my radiators?
Once or twice a year is usually enough. If you refill or notice noises mid-season, bleed them again.
If you need help with your heating or boiler, our local engineers are here to help. Call us on (01420) 558993
Written by Embassy Gas — your local heating experts covering Bordon, Alton, Liphook, Farnham and surrounding areas.