Why is my boiler losing pressure? Causes and solutions

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A boiler losing pressure can be a frustrating issue, leading to inefficient heating, cold radiators, and even system malfunctions. If you’ve noticed your boiler pressure dropping, it’s important to identify the root cause and address it promptly to prevent further complications. In this guide, we’ll explore the common reasons for boiler pressure loss and the best solutions to fix the problem.

Common Causes of Boiler Pressure Loss

1. Leaks in the System

One of the most frequent reasons for a drop in boiler pressure is a leak somewhere in the system. Leaks can occur in pipes, radiators, or even inside the boiler itself. Even a small leak can gradually reduce pressure over time.

How to Check: Look for visible water stains around pipes, radiators, or beneath the boiler. If you suspect a leak but can’t find it, a heating engineer can perform a pressure test.

Solution: If you find a leak, contact a qualified plumber or heating engineer to repair it. Do not attempt to seal leaks with DIY fixes, as this could cause further damage.

2. Bleeding Radiators

If you have recently bled your radiators, you may have inadvertently released water from the system, leading to a drop in pressure.

Solution: After bleeding your radiators, always check the boiler pressure gauge. If it’s too low, repressurize the system using the filling loop (as per your boiler’s manual).

3. Faulty Pressure Relief Valve

The pressure relief valve (PRV) is designed to release excess pressure from the boiler. However, if it’s faulty or has been triggered too frequently, it can allow water to escape, leading to pressure loss.

Solution: If you suspect a faulty PRV, it’s best to call a professional to inspect and replace it if necessary.

4. Expansion Vessel Issues

The expansion vessel in a boiler maintains the right level of pressure as the water heats and expands. If the vessel is faulty or under-inflated, the pressure can drop too quickly.

Solution: A heating engineer can check and repressurize the expansion vessel or replace it if needed.

5. Aging or Faulty Boiler Components

Older boilers can develop wear and tear, leading to internal component failures that cause pressure drops.

Solution: If your boiler is more than 10-15 years old and regularly loses pressure, it might be time to consider replacing it with a newer, more efficient model.

How to Repressurize Your Boiler

If your boiler’s pressure has dropped below the recommended level (usually between 1 and 1.5 bar), you can try repressurizing it using the filling loop.

  1. Turn off the boiler and let it cool.
  2. Locate the filling loop (usually a flexible silver or braided hose under the boiler).
  3. Slowly open the valves to allow water into the system while keeping an eye on the pressure gauge.
  4. Close the valves once the pressure reaches the correct level.
  5. Turn the boiler back on and check for proper functioning.

If the pressure continues to drop frequently, consult a professional as there could be an underlying issue.

Final Thoughts

A boiler losing pressure can be caused by several factors, from leaks to faulty components. Regular maintenance, annual servicing, and addressing minor issues early can help keep your heating system running smoothly. If you’re unsure about the cause or solution, don’t hesitate to seek help from a Gas Safe registered engineer to ensure safety and efficiency.