Low boiler pressure can put a real dampener on your winter. It can cause the boiler to endlessly trip, or might simply stop it from heating up properly or running efficiently. There are a few common causes of low boiler pressure, which we’ll deal with in this article. Some can be fixed by the homeowner or tenant, while others might point to a deeper problem, which can only be fixed by a visit from a central heating professional.
Let’s take a look at what might be causing your problem, and whether it’s something you should attempt to tackle yourself.
What is boiler pressure?
Having the correct boiler pressure is vital to keeping your central heating and hot water working. It’s essentially the balance of internal pressure in the system – a key aspect to ensure water circulates properly. Most residential boilers work perfectly fine with a pressure gauge reading between 1 and 2 bars when they’re cold.
If it’s too low, your system might not operate effectively, leaving your home cold and those showers less than luxurious. If it’s too high, it can cause damage to the system, or cause it to run inefficiently. Usually, the boiler’s own safety measures will stop any damage happening by switching itself off, but you probably shouldn’t rely on that happening – if your pressure is low, you should deal with it.
Common causes of low boiler pressure
Now, let’s move onto the possible causes of low boiler pressure. Some are obvious, and some will need professional diagnosis.
Leaks in the system
One of the most frequent causes of low boiler pressure is leaks. Even a small drip can cause a notable drop in pressure over time, just as a tiny hole in a tyre will cause it to deflate over time. Remember – the heating is a closed loop, so if pressure drops, there’s no way for it to magically rise all by itself.
Check all visible pipes, radiators, valves and joints. Leaks often appear as damp patches or small puddles around pipes and valves. Even if it seems minor, it’s worth investigating, as water escaping from the system means pressure escaping too.
Bleeding radiators
You might have recently bled your radiators to improve heating. But releasing the trapped air will probably also release some system pressure. It’s a delicate balance. After bleeding, check your pressure gauge. If it has dropped, you’ll need to top it up before all your radiators heat evenly again.
Faulty pressure relief valve
The pressure relief valve acts as a safety feature, releasing excess pressure to prevent damage. If it is faulty, it might be letting out water even when it shouldn’t, causing pressure loss. Have a look at this valve, often located near the boiler, for any signs of water discharge or corrosion.
Issues with the expansion vessel
The expansion vessel absorbs the expanding water as it heats. If the pressurised air in this vessel depletes or if there’s a fault, it might not function correctly, resulting in pressure problems. Signs include the boiler pressure rising too quickly when the system is on, then dropping off when it’s off.
Water loss from the boiler
As well as leaks from the pipes, sometimes water can escape directly from the boiler itself. This isn’t about visible leaks but more about internal issues like a broken seal or faulty component. Look underneath the boiler for any signs of accumulated water. Otherwise, it’s a task for a professional.
Diagnosing low boiler pressure
Before attempting fixes, it’s a good idea to gauge the situation. Here’s how:
- Check the pressure gauge: The gauge is either an analogue clock with a pointer, or a digital readout on a panel (check your manual for details). If it’s below 1 bar, you’re too low.
- Look for visible leaks: Having a quick look around the system for damp spots or puddles can save you time. Note that leaks could be under floorboards or behind skirting boards, so finding nothing doesn’t necessarily rule it out.
- Recent changes?: Think back on recent repairs or maintenance – has anything changed recently, such as bleeding or new components being installed?.
Next steps
If your boiler pressure is low, don’t panic. Often, it’s easy to remedy.
Repressurising the boiler
You can often remedy low boiler pressure by repressurising it yourself. Here’s a simple guide, but it does vary from system to system:
- Turn off the boiler: Make sure the system is cool.
- Locate the filling loop: This is often a flexible detachable hose that came with the boiler, while other times it is permanently connected pipework. Connect the two ends (if necessary). Refer to your manual to find where to connect it.
- Open the valves: Turn the valves slowly to let water into the system. You’ll hear it filling.
- Watch the pressure gauge: Once it’s between 1 and 2 bars, turn the valves back to their original positions.
- Switch the boiler on: Monitor if the pressure stays stable.
If you’re not comfortable carrying this out, don’t hesitate to call in a professional.
Professional help
Sometimes, the cause of low pressure requires more than a DIY fix. If you can’t find any leaks and you suspect a malfunctioning component, book a boiler inspection and repair. A professional will accurately diagnose your system and sort issues that might be found.
Preventative measures
Keeping your boiler in top shape is easier than dealing with issues as they arise. Here are some tips:
- Regular maintenance: Make sure you always have your annual boiler service completed. Engineers can spot potential problems before they become costly repairs.
- Monitor regularly: Occasionally glance at your pressure gauge, especially after bleeding radiators or if you suspect changes.
- Stay informed: Keep the boiler manual handy. It provides valuable insights into your model.
Here’s to a warm home
Knowing why your boiler pressure is low and what to do about it can save you from cold showers and high bills. Remember, some things are best left to professionals, particularly if you’re unsure about handling things yourself. Prompt attention keeps your boiler running smoothly, your home warm, and your water hot.