Understanding Boiler Pressure
Your boiler's pressure gauge should normally read between 1.0 and 1.5 bar when the system is cold. If the pressure drops below 1 bar, your boiler may shut down to protect itself. If it rises above 3 bar, the pressure relief valve will discharge water outside to prevent damage.
Pressure loss is a very common problem for homeowners across Hull, Beverley, Kingswood, and East Yorkshire. While sometimes it's a simple fix you can do yourself (repressurising via the filling loop), persistent pressure loss almost always indicates an underlying issue that needs a Gas Safe registered engineer to diagnose and repair.
Common Causes of Boiler Pressure Loss
Water Leak in the System
The most common cause. A slow leak from a radiator valve, pipe joint, or the boiler itself will gradually reduce pressure. Even a tiny drip can drop the pressure over days or weeks.
Faulty Pressure Relief Valve (PRV)
The PRV is a safety device that releases water if pressure gets too high. If it's faulty or passing, it will let water escape continuously, dropping your pressure.
Faulty Expansion Vessel
The expansion vessel absorbs pressure changes as water heats and cools. If the vessel loses its charge or the diaphragm splits, pressure will spike when heating and then drop rapidly.
Leaking Automatic Air Vent
Air vents can develop leaks that allow water to escape. This is often found inside the boiler casing and may not be visible without opening the unit.
Bleeding Radiators
If you've recently bled your radiators, you'll have released air and lowered the system pressure. Simply repressurise using the filling loop.
Cracked Heat Exchanger
A more serious issue—a cracked heat exchanger will leak water internally. This usually requires boiler replacement rather than repair.
How to Repressurise Your Boiler
If your boiler pressure has dropped below 1 bar, you can try repressurising it yourself before calling an engineer:
- 1. Locate the filling loop—a braided silver hose connecting two pipes underneath or near your boiler.
- 2. Open both valves slowly. You should hear water flowing into the system.
- 3. Watch the pressure gauge and stop when it reaches 1.2-1.5 bar.
- 4. Close both valves firmly.
- 5. Reset your boiler if needed and check it fires up correctly.
If your pressure drops again within a few days, you have a leak or faulty component. Do not keep repressurising—call us to find and fix the root cause.
Boiler Pressure FAQs
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