Understanding Low Pressure in Your Central Heating System

A Guide for Customers wanting to understand the causes and effects.

Introduction

Central heating systems and boilers are largely ignored in our homes. The boiler is shut away in a cupboard or up in the loft and you go on with your daily life having showers and cranking up the heating, especially when the weather turns chilly. They keep us warm and comfortable, but only if they’re working efficiently. One of the key factors in their performance is maintaining the correct pressure. If your system’s pressure is too low, it can lead to poor heating, cold radiators, and even damage to the boiler. If the pressure is too high then it could damage system components or cause a catastrophic leak. In this blog post, we'll explain low pressure in central heating systems, why it happens, how our customers in Bognor Regis and surrounding areas can fix it, and share some tips to keep your system in tip-top shape.

If you think you need a professional then please get in contact with us at The Sussex Heating Care Company and we will be happy to help. Contact | New boiler Bognor Regis, Chichester, Littlehampton

What Causes Low Pressure?

Low pressure in a central heating system is a common issue, and it’s often nothing to panic about. The usual suspects include:

• Leaks: Even the smallest leak in pipes, radiators, or the boiler itself can cause pressure to drop.
• Bleeding Radiators: Letting air out of your radiators to improve heating can also release some water, which lowers the pressure. Before bleeding your radiators, make sure you know how to top up the system pressure afterwards.
• Faulty Valves or Flat Expansion Vessels: Sometimes, the pressure relief valve or other components may be faulty, allowing water to escape when it shouldn’t.

Spotting the cause early can save you time and hassle down the line. An annual boiler service will go a long way in preventing these problems. Contact | New boiler Bognor Regis, Chichester, Littlehampton

Why Does Low Pressure Happen?

If you have a pressurised central heating system, it is a closed circuit filled with water, like a balloon is filled with air and then sealed. The pressure is what helps circulate hot water to your radiators and back to the boiler and helps to reduce air getting into the system causing airlocks and corrosion. If water escapes—whether through leaks, maintenance, or faulty parts—the pressure drops. This means your boiler has to work harder, and your heating won’t be as effective.

Your boiler maybe fitted with a system pressure sensor which will stop the boiler working in the event the pressure drops too low, protecting the boiler from damage caused by poor circulation and overheating.

How To fix Low System Pressure?

Fixing low pressure is usually straightforward, and you don’t need to be a plumbing whizz to get it sorted. It is considered normal to top up the pressure every 6 months or so. Here’s a simple step-by-step guide:

1. First, check your boiler’s pressure gauge. Most boilers have a dial—if it’s below 1 bar, the pressure is too low.
2. The boiler shouldn’t be running when carrying out these checks, turn off your heating and let the system cool down.
3. Locate the filling loop (usually a silver, flexible hose beneath the boiler, with a valve on each end).
4. Open the valves on the filling loop slowly. You should hear water entering the system.
5. Keep an eye on the gauge, it should rise gradually. Once it reaches between 1 and 1.5 bar, close the valves. If the pressure rises too quickly you may have a flat expansion vessel.
6. Switch your boiler back on and check if your radiators are warming up properly.

If the pressure keeps dropping, there may be an underlying issue that needs attention.

A little maintenance goes a long way. Here are some prevention tips:

• Check your system’s pressure regularly, especially before winter.
• Inspect visible pipework and radiators for signs of leaks or corrosion.
• Bleed your radiators only when necessary, and top up the pressure afterwards.
• Arrange for annual servicing by a qualified heating engineer to catch problems early.

Prevention is always better than cure, and regular checks can help you avoid that cold shower when you’re already in a rush.

Leaks are the most common reason for pressure loss. Here’s how to spot them:

• Look for damp patches or water stains around pipe joints, radiators, and beneath the boiler.
• Check for hissing sounds, which could indicate escaping water or steam.
• If your boiler has a bottom cover, inspect it for pooled water or water marks.
• Go outside and look to see if the pressure relief pipe is dripping.

If you suspect a leak but can’t find it, or if the leak is tucked away under a floor, it’s time to call in a professional. Trying to carry out major repairs yourself can sometimes do more harm than good and you also may not be qualified to deal with some the issues you come across. Plumbing and heating is easy when everything is going to plan but when it goes wrong you need to work out how to fix it. In the words of Mike Tyson “everyone’s got a plan until they get punched in the mouth”

Can I Just Add Some Leak Sealer?

There are products on the market that can be added to the system water to plug up small leaks on the system. Leak sealer definitely has its uses, such as a small leak on a pipe under a tiled floor.

If the leak can be repaired properly by replacing a component, joint or length of pipe then always do the repair.

Leak sealer can cause problems of its own, blocking up air vents or collecting dirt in the system, use should be avoided where possible.

What Happens If I Keep Topping Up?

It might be tempting to keep topping up the pressure and hope for the best. However, this can cause more issues in the long run:

• Constantly adding water can lead to corrosion inside the system, shortening its lifespan.
• Build up of corrosion will narrow water ways and reduce circulation.
• You might mask a serious leak that could worsen over time, leading to costly repairs and even damage to your property.
• Excessive topping up can also put strain on your boiler and its components, risking breakdowns.
• Persistent leaks and topping up regularly are one of the leading causes of boiler breakdown which quickly leads to it needing replacing.

The best approach is to fix the underlying issue rather than just treating the symptom.

Conclusion

Low pressure in your central heating system isn’t the end of the world, but it’s important not to ignore it. Ignoring the problem is only going to lead to a bigger repir bill in the future. By understanding the causes, knowing how to re-pressurise your system, and staying vigilant for leaks, you can keep your home cosy and avoid bigger headaches down the line. Remember, regular maintenance and prompt action are your best friends when it comes to keeping your central heating in tip-top condition. If ever in doubt, don’t hesitate to reach out to a qualified professional.