Why Boiler Pressure Drops Overnight
When your boiler pressure drops overnight, it can be frustrating to wake up to a heating system that isn’t performing as it should. Many homeowners experience this problem, especially during colder months when boilers are working harder. Understanding the causes behind pressure loss can help you decide whether it’s a simple fix or time to call in a professional.
What Causes a Drop in Boiler Pressure
Leaks in the Heating System
Small leaks are one of the most common reasons for pressure loss. These leaks may not always be visible and can occur anywhere in the system, from radiator valves to joints under the floorboards. Even the tiniest drip can cause the pressure to drop over several hours.If you notice damp patches, corrosion around fittings, or water beneath the boiler, it’s best to turn off the system and call an engineer. Leaving a leak untreated can lead to costly damage and reduce the efficiency of your heating system.
Faulty Pressure Relief Valve
Every boiler is equipped with a pressure relief valve to release excess pressure and prevent dangerous buildup. However, if this valve becomes worn or starts leaking slightly, it can allow water to escape, leading to pressure drops when the system cools down. This is a safety component that should only be inspected or replaced by a Gas Safe registered professional. Attempting to fix it yourself could cause further damage or void your boiler’s warranty.
Air Trapped in the Radiators
If you’ve recently bled your radiators or had work done on your heating system, trapped air could be to blame. Air pockets stop water from circulating properly, causing pressure to fluctuate. You might notice that some radiators are warm at the bottom but cold at the top, a clear sign that air is trapped. Bleeding your radiators can help restore balance, but if the pressure drops again shortly after, it suggests a deeper issue within the system that needs professional diagnosis.
Problems with the Expansion Vessel
The expansion vessel is a key component inside your boiler that manages pressure changes as water heats and cools. Over time, the vessel can lose its air charge or the internal diaphragm can fail, preventing it from maintaining stable pressure. When this happens, your boiler may seem fine during the day but lose pressure as it cools overnight. This fault often requires a skilled heating engineer to re-pressurise or replace the vessel to restore proper system function.
Recent Repairs or Maintenance Work
If you’ve had recent plumbing work, radiator replacements, or a power flush, your system may need to be topped up. Air can enter the system during maintenance, and it’s normal to see minor pressure drops afterwards. Re-pressurising through the filling loop should resolve it, but if it doesn’t, there may be an underlying issue such as a hidden leak or failing component.
Seasonal Temperature Changes
Cold weather can also play a small role in overnight pressure drops. As the water in your system cools, it contracts slightly, leading to a small dip in pressure. However, if it continues to fall below 1 bar every night, it’s likely more than just temperature-related and worth investigating further.
When to Call a Professional
It’s important not to ignore frequent pressure drops, even if they seem minor. A consistently low-pressure boiler can become inefficient, increase energy use, and risk damage to vital parts like the heat exchanger. A qualified Gas Safe engineer can carry out a thorough inspection, check for leaks, test components such as the expansion vessel and pressure valve, and ensure your system is working safely and efficiently.
Need Help Fixing Boiler Pressure Issues in Dartford, Sidcup, or Bexley?
If your boiler pressure keeps dropping overnight, Summit Plumbing & Heating Solutions Ltd can help. Our experienced Gas Safe engineers provide expert diagnostics, repairs, and maintenance to restore your boiler’s performance and reliability. Call us today on 07947 403269 or fill out our online contact form to book a professional inspection.
