Waking up to low boiler pressure can be alarming, especially in Whitehill when chilly nights are common. A drop below the normal range, typically 1.0–1.5 bar, can cause heating breakdowns and cold radiators. This guide explores why your boiler keeps losing pressure overnight, focusing on leaks and expansion vessel faults in Whitehill and nearby areas like Bordon, Liphook and Farnham. We’ll also outline practical checks and when to seek professional help, from new boiler installation to routine maintenance.
Common Causes of Boiler Pressure Loss
Leaks in the System
One of the most frequent culprits is water escaping from the sealed heating system. Leaks can occur at:
- Radiator valves or pipe joints, leading to visible dripping or damp patches
- The boiler’s pressure relief valve, releasing water if pressure gets too high
- Internal components such as the heat exchanger, which may corrode over time
Unchecked leaks result in a gradual drop of pressure overnight, especially during colder temperatures when the system is at rest.
Faulty Expansion Vessel
The expansion vessel accommodates water volume changes as the boiler heats up. It contains a rubber diaphragm separating the water from compressed air. If the diaphragm fails or the vessel loses air charge, it cannot absorb pressure spikes. The result? The safety relief valve discharges water, causing pressure loss.
Signs of an expansion vessel fault include a boiler that ‘kicks out’ with an error code or hisses after heating. Recharging or replacing the vessel often requires a qualified Gas Safe engineer to avoid more serious leaks or a complete heating breakdown.
Troubleshooting Steps
Before calling for professional help, you can perform basic checks:
- Check the Boiler Pressure Gauge: Ensure it is between 1.0 and 1.5 bar when cold. If it’s below, use the filling loop to repressurise following your boiler manual.
- Inspect for Visible Leaks: Look around radiators, pipework, and under the boiler for watermarks or puddles.
- Bleed Radiators: Air trapped in radiators can affect system balance. Use a bleed key to release any air, then top up boiler pressure.
- Monitor the Expansion Vessel: Gently tap the vessel; a hollow sound indicates proper air charge, while a dull thud suggests waterlogged conditions.
When to Call a Gas Safe Engineer
If leaks persist or you suspect an expansion vessel fault, it’s time to call in the experts. A professional can carry out a full boiler servicing to identify hidden leaks, test safety components, and recharge or replace the expansion vessel safely.
In older properties around Whitehill (GU35) or nearby Hindhead, Liphook and Haslemere, corrosion may hide inside pipework or the boiler itself. Regular servicing helps prevent unexpected heating breakdowns and extends the life of your system.
Preventative Tips
- Schedule annual boiler servicing and consider a comprehensive boiler cover plan for peace of mind
- Maintain water quality – use inhibitor fluids to reduce corrosion
- Keep an eye on pressure gauges and act quickly if you see unusual drops
Frequently Asked Questions
Why does my boiler pressure drop every night?
Pressure often drops due to minor leaks or a faulty expansion vessel releasing water when the system cools.
How do I repressurise my boiler?
Locate the filling loop under the boiler and open the valves until the gauge reads about 1.2 bar. Close the valves and restart the system.
Can a faulty expansion vessel cause continuous leaks?
Yes. If the vessel loses its air charge, the safety valve will open to relieve pressure, leading to ongoing leaks.
Looking for Expert Help?
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.