Boiler pressure explained
A gas boiler breakdown means no hot water and no heating… which is never a good thing. Your boiler can stop working for several reasons, one being because your boiler pressure is too low or too high.
It’s fairly simple to find out if a problem with the pressure is why your boiler has stopped working. And there are some easy ways you can try to fix the problem yourself.
Why is boiler pressure important?
Gas central heating keeps your home warm by heating cold water and pumping it around your pipes and radiators.
Most central heating systems are sealed. This means there are no vents to manage the water expanding and contracting as it heats and cools. Instead, the system is pressurised and must maintain a stable pressure to move the water around your home efficiently.
How do I check my boiler pressure?
Most gas boilers will have a pressure gauge on the front of your boiler showing what the current pressure is.
Some pressure gauges have a single needle, with low and high pressure shown by red areas on the dial. Others have two needles, with a red one acting as a marker for where the pressure should be and a black one showing where it is. Some boilers may display the pressure on an LCD screen and may flash or show an error message if the pressure is too high or too low.
The ideal pressure for your boiler is usually between 1 and 2 bars, but it’s possible it could go up to 2.5 bars when your heating is on. Check the boiler manual to find out exactly what it should be for your boiler make and model.
If the boiler pressure is below 1, that means low pressure. This could be because you’ve lost water from your heating system. If the pressure gauge goes above 2.75, that usually means it’s too high. You may need to bleed a radiator or get an engineer to check for an underlying fault.
Why has my boiler pressure dropped?
Unless you check your boiler pressure gauge regularly, you might not notice the pressure is dropping. But if you suddenly have no hot water or your radiators fail to heat up, your boiler may have stopped working due to the pressure being too low.
There are two main reasons for low boiler pressure:
- Water leak
A leak means water being lost from your system, lowering the pressure. It could be small and unnoticeable, but if it goes on for long enough, your pressure will slowly drop. Check around your pipes, radiators, and even your boiler for water or damp patches. Don’t try to look inside your boiler though – you’ll need a Gas Registered engineer to do that.
- Bleeding radiators
Bleeding your radiators takes water out of your central heating system, lowering the boiler pressure.
What can I do about low boiler pressure?
It’s possible to fix low pressure yourself, however, you should check your boiler’s manual before you start.
To re-pressurise your boiler, you’ll need to let more water into the system using something called a filling loop. These can be built into your boiler or come as an attachment. The filling loops design and the filling process can vary, but here’s a basic guide on what to do:
- Turn off your boiler and allow it to cool.
- Find the filling loop, or attach it to your boiler.
- Make sure you can see the boiler pressure gauge while using the filling loop.
- Open the valves on both sides to let water into your system.
- Wait until the pressure gauge reaches 1.5 bar then close each valve, one after the other.
- Switch your boiler back on and, if you need to, press the reset button.
- Don’t forget to remove the filling loop if it’s an attachment. Be careful in case there’s any water left in it.
If your pressure drops again, or you’re unsure about trying to re-pressurise your boiler, it’s best to get a professional to have a look at it.
What can I do about high boiler pressure?
In the same way a boiler responds when the pressure gets too low, if your boiler’s pressure becomes too high, it may automatically turn off. The likely reasons your boiler pressure may be too high are:
- Too much water in the heating system
If you’ve recently added water to your system due to low pressure this may be the culprit. A simple fix is to bleed your radiator. This lets some of the water out and so should reduce the pressure.
- Faulty boiler
If bleeding your radiators doesn’t work, one of the boiler parts could be faulty. Contact a Gas Safe Registered engineer to investigate.
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