Combi Boiler Losing Pressure But No Leak Found? Our Emergency Engineers Can Diagnose Fast

Waking up to a cold house because your combi boiler has lost pressure is a stressful start to the day. You’ve checked under the boiler and around radiators but can’t find a single drip. No leak? The problem feels even more baffling. This is a classic emergency call-out scenario for our team. When your boiler pressure keeps dropping and you can’t see why, you need a fast, expert diagnosis to get your heating and hot water back online.

Why Your Boiler Loses Pressure When No Leak Is Visible

The most common reason a combi boiler loses pressure without a visible leak is a fault with the pressure relief valve or the expansion vessel. The pressure relief valve is a safety device that can start to discharge water externally if it fails, often via a small pipe outside that you might miss. The expansion vessel, which accommodates expanding hot water, can lose its air charge, causing the system pressure to spike and then drop as the relief valve operates. Other culprits include a faulty internal component like the heat exchanger or a failed pressure gauge itself. These issues aren't just inconvenient; they can lead to a complete boiler shutdown, leaving you without heating.

Our 24/7 Emergency Response For Pressure Loss

We treat unexplained boiler pressure loss as an urgent priority. Our engineers are on call around the clock because these problems don’t wait for business hours. When you call, we dispatch an engineer to your location promptly. They arrive equipped to perform a systematic diagnosis, checking the expansion vessel charge, testing the pressure relief valve, and inspecting the boiler and its external discharge pipe. We move quickly to identify the exact component at fault so we can advise on the necessary repair. Our goal is to restore your system’s stability and your peace of mind without delay.

Immediate Actions To Take Before We Arrive

While you wait for our engineer, there are a few safe steps you can take. First, do not repeatedly re-pressurise the system using the filling loop. This can temporarily mask the symptom but risks causing further damage if the relief valve is discharging. Check the very end of the pressure relief valve discharge pipe outside your property for any signs of dripping water. If you feel comfortable, you can also check around the boiler itself for any minor signs of moisture. Make a note of how often the pressure drops and from what reading. This information helps our engineer diagnose the issue faster upon arrival. If the boiler has locked out, leave it off and focus on staying warm.

Ignoring a recurring pressure loss, even without puddles, risks more severe damage. A constantly cycling relief valve can fail completely, and an undercharged expansion vessel puts strain on the entire system. Our emergency engineers provide a definitive solution, whether it’s recharging an expansion vessel, replacing a faulty valve, or sealing an internal leak. We get your boiler holding pressure correctly so you can regain reliable heat and avoid a costly total breakdown. Don’t spend another night trying to top up a failing system—call for urgent, expert diagnostics and repair.