From cold to cosy. Fixing low boiler pressure.

leaf looking at boiler

It’s easy to feel overwhelmed when you have to navigate the chilly waters of your boiler losing pressure - and the loss of your heating and hot water.

Whether you’re (shivering and) wondering why your radiators have given you the cold shoulder, or you've just noticed that your boiler's pressure gauge is looking a bit low, understanding what's going on and how to fix it can be a game-changer. 

So, let's snuggle up and look at what causes your boiler pressure to drop, and how you can get things up and running again.

Clues to your boiler pressure loss.

You should take into consideration how the pressure in your boiler is dropping. It can help you eliminate the likelihood of certain problems and give you an idea of where to start looking.

Is it a sudden drop in pressure? That would suggest a leak. A gradual loss might be something simple (like too much air in the system) but it could point to something more complex.

What's causing my low boiler pressure?

First off, let's just say a drop in boiler pressure may not be the disaster you first think it is. Your boiler can often lose pressure simply because of a change in the weather. 

Another common cause of a drop in boiler pressure is bleeding your radiators. You need to do this when there is air caught in your system. Air doesn’t conduct heat as well as water and your radiators won’t feel as hot if there is too much air in your system.

The problem is, it’s easy to let out water as well as air when you bleed your rads, and this can lead to a drop in pressure.

In these situations, the thing to do is to bring the pressure back up (see below). This can quite often sort out the problem. However, if that doesn’t work, or you want to check every option, then continue reading…

Troubleshooting boiler problems.

A leaky system is often the suspect when it comes to a drop in boiler pressure. You might not see a dramatic gush, but even a tiny leak can cause your boiler pressure to take a nosedive over time.

And there are several places where your system can leak. You should check:

  • Around your radiator valves for signs of water leaks. Even a tiny leak can lead to a large pressure drop over time.

  • Exposed pipework. Because it’s exposed, it’s more vulnerable to damage. Again, check for signs of water. In this case you may need a professional plumber for repairs.

  • The Pressure Release Valve (PRV) is designed to expel water if the pressure gets too high. If it's faulty, it might leak even within normal pressure ranges. Look for drips or wet patches around the PRV, especially where it’s connected to an external pipe.

  • Boiler components like the heat exchanger can develop leaks that are harder to detect. If you've eliminated other causes, you may well have an internal leak.

Then there's the thermostat – this little device can be the heart of the problem when your heating is acting up. If your home's feeling more like an ice cave than a snug den, the issue might just lie with a misbehaving thermostat failing to signal your boiler properly.

The thing is, a faulty thermostat itself doesn’t directly cause a drop in boiler pressure. However, there are indirect ways a thermostat issue can contribute to pressure loss:

  • A faulty thermostat might cause the boiler to turn on and off more frequently than usual. This “short cycling" can put stress on the system and may lead to leaks developing over time. Leaks, as discussed earlier, are a major cause of pressure loss.

  • If the thermostat malfunctions and gets stuck in the "on" position, the boiler could overheat. A safety feature, the PRV, might activate to release pressure and prevent boiler damage. This release of pressure would require you to repressurise the system afterwards. However, a faulty PRV that leaks even at normal pressure ranges could also be the culprit.

In both these scenarios, the pressure loss is caused by the consequence of the faulty thermostat, not the thermostat itself.

If you suspect a faulty thermostat, it's recommended to get it checked by a qualified engineer. A properly functioning thermostat helps maintain an even temperature and avoids putting unnecessary stress on the boiler system, potentially preventing pressure loss issues in the long run.

And let's not forget about those freezing nights. If you've got a condensing boiler, a frozen condensate pipe could be your culprit. This pipe is there to expel waste water outside.

If this pipe gets blocked with ice because of the low temperature, your boiler may well have a safety mechanism to shut it down, leading to a drop in the pressure.

How do you fix boiler pressure issues?

DIY boiler repairs.

It may feel daunting, but you can try to repressurise your boiler yourself. It's not rocket science, honest! 

Just make sure your boiler's cooled off and locate the filling loop (that's your key to adding water back into the system). You’ll usually find it amongst the pipes coming out of your boiler and it looks like a silver braided pipe with a black tap at either end.  

If the loop looks like it’s leak free and generally in good condition, then gently open a tap up to get the pressure back to around 1.5 bar and then close the tap. Finally, fire up your boiler and see if things improve. Keep a cloth handy as a small amount of water may escape during the process.

How to check your boiler pressure.

Make sure your boiler is running at the correct pressure with our simple walkthrough guide on how to check water pressure on a boiler.

Leak hunt.

Gear up for a little detective work and hunt down any sneaky leaks. Keep your eyes peeled for damp spots or mysterious puddles – these are your clues. The most likely places where leaks occur are at joints, or bends, or where the pipework is exposed. Remember, even the smallest leak can be the villain behind your boiler's pressure drop.

Unblocking a frozen pipe.

If you have an external pipe from your condensate boiler that is blocked with ice, you could carefully pour warm water over it to help the ice melt. Alternatively, if you feel it is not safe to pour warm water over the pipe you can always place a hot water bottle on the pipe. 

It’s important to note that you shouldn’t pour boiling water, antifreeze or salt on the frozen pipe as these can all damage it.

And finally, once the pipe is unblocked, check it for any cracks or leaks. Water expands when it freezes and this on its own can crack your pipework.

Time to bring in the experts.

Of course, if you’re not sure of what to do or if your boiler pressure keeps failing despite your best DIY efforts, then it's time to reach out to a Gas Safe registered engineer. They're like boiler whisperers, ready to dive in and sort things out, whether it's a persistent leak, a faulty thermostat or the need for a more serious fix.

And should you have to get your boiler replaced, make sure you use a reputable company for top flight service. 

Boiler maintenance tips.

As is often the case, prevention is better than cure. So, to keep your boiler from freezing you out in the future, check the pressure regularly and don't forget that all-important annual service. It's like a spa day for your boiler, ensuring it's ready to keep you cosy all year round. And with a cover package like HomeServe, you can spread the cost over the whole year.

And there you have it – with a bit of know-how and sometimes a helping hand, you'll have your boiler humming happily again in no time. Remember, a happy boiler means a warm and welcoming home, so take good care of it, and it'll do the same for you.

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Published 07/04/2024