Introduction
Bleeding radiators is a routine task for homeowners in Wickham and surrounding Hampshire villages like Bordon (GU35), Alton and Liphook. It helps release trapped air, improving heat distribution and reducing cold spots. However, many people notice their boiler pressure falling below the recommended level after venting radiators. In this guide, we explain the link between bleeding and pressure drops, offer troubleshooting steps, and share practical advice for Wickham households.
Understanding Boiler Pressure
Why Boiler Pressure Matters
Your boiler operates under a sealed water circuit. The correct system pressure (usually between 1 and 1.5 bar when cold) is crucial for efficient heating. If pressure falls too low, the boiler may lock out, radiators won’t heat fully, or the system could even display warning lights. A sudden overnight dip after bleeding radiators is a common cause of morning chills and a heating breakdown.
Normal Pressure Levels
Most modern combi boilers feature a pressure gauge on the front. When the boiler is off and the system cold, you should see around 1.0 bar. When the heating is running or after hot water demand, the gauge can rise to 1.5–2.0 bar. If it drops below 0.5 bar, you risk a shutdown. Regular checks are a simple way to stay on top of radiator problems and boiler repair needs before they escalate.
How Bleeding Radiators Affects Pressure
The Role of Venting
Rad air pockets build up over time, especially in upstairs radiators, hindering performance. Bleeding lets this trapped air escape via the radiator valve. As air rises and exits, water takes its place inside the panel. But if you vent too much or the system isn’t correctly balanced, you also release some of the sealed water, lowering the overall system pressure.
Where Does the Lost Water Go?
When you open the bleed valve, both air and water escape. If your central heating system has multiple radiators or an unbalanced return pipe, you could lose more water than anticipated. That water needs topping up via the filling loop or a pressure gauge refill point. Without it, the boiler pressure stays low, causing cold spots and potential system faults.
Troubleshooting Low Pressure
- Check the Pressure Gauge: Confirm the level is under 1.0 bar before restarting. Use your boiler manual to find the correct cold-pressure figure.
- Re-Pressurise the System: Locate the filling loop beneath your boiler and open the valves slowly. Watch the gauge; close both valves once you reach around 1.2 bar.
- Inspect for Leaks: Look around radiators, pipe joints, the boiler body, and valves. Leaks will allow air in and water out, causing repeated pressure loss.
- Check the Expansion Vessel: A faulty diaphragm can mean the vessel fails to absorb pressure fluctuations, leading to drops after venting.
Practical Guidance for Wickham Households
In Wickham, older properties with large radiator arrays in Petersfield and Haslemere might see more air build-up. Ensure you bleed radiators in a systematic order—top floor first, then ground floor. Keep a small container to catch water and a cloth to prevent drips onto floorboards.
If you struggle to locate or operate your filling loop, or if pressure keeps dropping, consider booking a service with a Gas Safe engineer for boiler servicing. Regular maintenance in Whitehill, Liss or Grayshott can prevent future heating breakdowns and costly new boiler installation down the line.
Maintaining Proper Pressure Over Time
Frequent pressure checks, especially after long vacations, help you spot gradual leaks. Consider adding comprehensive boiler cover for peace of mind during colder months in Farnham or Hindhead, ensuring prompt repairs if you hit a cold snap.
When to Call a Gas Safe Engineer
If you repeatedly lose pressure even after re-pressurising, or if you notice corrosion, odd noises from the boiler, or persistent radiator cold spots, it’s time to call a qualified engineer. They can perform thorough diagnostics, fix leaking valves, or replace a faulty pressure relief valve to keep your system operating safely and efficiently.
Frequently Asked Questions
1. Why does my boiler pressure drop after every bleed?
Each time you bleed a radiator, a small amount of water leaves the system with the air. If you bleed multiple radiators without topping up, the cumulative loss can cause a noticeable pressure drop.
2. Can I re-pressurise the system myself?
Yes—most boilers have a built-in filling loop. Close the boiler, open the valves slowly, and watch the gauge. Stop once you reach around 1.2 bar. If you’re unsure, contact a professional.
3. How often should I bleed my radiators?
Once or twice a year is usually sufficient. Bleed radiators when you notice cold spots or at the start of the heating season to ensure optimal performance.
4. Will a leaking radiator valve cause pressure loss?
Absolutely. Even a small drip lets water escape and air enter, driving down pressure. If you spot a leak, schedule a boiler repair to replace the faulty valve.
If you need help with your heating or boiler, our local engineers are here to help. Call us on (01420) 558993 or book online at embassygas.com/book.
Written by Embassy Gas — your local heating experts covering Bordon, Alton, Liphook, Farnham and surrounding areas.