Why is My Boiler Losing Pressure? Causes & Fixes Re March 11, 2020

Why is My Boiler Losing Pressure? Causes & Fixes

Boiler losing pressure

Why is My Boiler Losing Pressure? We cover all the reasons why your boiler keeps dropping pressure and look at fixes.

We’ve all experienced that sinking feeling as you wake up and the house is freezing cold or you turn the shower on and the water doesn’t heat up, so you go and check on your boiler and see the boiler pressure gauge has dropped into the dreaded red zone.

But why? Why does your boiler lose pressure? There are lots of reasons why your boiler drops pressure and we’re going to look at all of them and wherever possible offer solutions to get your boiler pressure back up and get your heating and hot water on again.

It’s important for your boiler to maintain a steady pressure, too high or too low a pressure level, and the boiler will switch off. It requires pressure to force water around your central heating system. Without the correct pressure, it can’t heat your home as it should.

What should my boiler pressure be?

The sweet spot for your boiler pressure is 1.5bar, this is in the middle of the ideal range of between 1-2 bar. Most boiler manufacturers recommend an optimal pressure of 1.3bar, but don’t worry if it’s not quite exact, as long as it’s within the working range you won’t have a problem. 

It doesn’t matter whether you have a Vaillant, Worcester, Baxi or Ideal boiler, the recommended boiler pressure is the same for all major boiler brands.

A boiler’s pressure will increase as it heats up and drops if it’s turned off. It’s only a small change in pressure but it does fluctuate. The pressure increases as you demand heating or hot water due to water expansion throughout your system.

Why does my boiler keep losing pressure?

A boiler can naturally lose pressure over a long period of time due to air escaping the system. If this is the case then just follow the steps in the section below to repressurise your boiler.

However, the most common cause for a combi boiler losing pressure is a leak. This can be due to a number of reasons including a leak caused by a faulty part in your boiler, a leak in your system from the pipes, a broken seal within the boiler, a faulty expansion vessel or a cracked heat exchanger. We categorise leaks as boiler leaks (coming from the boiler itself) or system leaks (coming from the pipes and radiators that make up your central heating system).

The first step is to identify where the leak is coming from. If it’s coming from the boiler itself or the pipes below the boiler then call a Gas Safe engineer to come and take a look as there is an issue with a boiler part that you are not legally allowed to fix, even if you know what the problem is.

Another common reason for a boiler losing pressure is caused by a leaking radiator valve. See the ‘how can I fix a radiator valve leak’ section if you are experiencing a leak coming from your radiator valve.

If you have recently bled your radiators and your boiler has switched off due to low pressure, this is likely the cause. When you bleed your radiators, you are releasing air from the system, this causes the pressure level in your boiler to drop. Just repressurise your boiler using the steps below and carry on as normal.

Recently had a new boiler installed? This is a common time for boiler pressure to drop in a system as air will often get into a system after a new boiler is installed, just repressurise your boiler and repeat as necessary.

Can I repressurise the boiler myself?

The good news is that, yes, you can repressurise the system yourself without the need to call out a Gas Safe engineer or a plumber. It is a fairly simple process that only takes a few minutes.

As mentioned above, if you have a leak coming from your boiler, call in the professionals. If you have a leak coming from your system then you can repressurise your boiler but it’s a matter of time before the pressure will drop again. You will need to fix the leak for the pressure on your boiler to stay at the correct level.

Every boiler is different, so we recommend referring to your boiler manual if you have it, or searching for it online if you don’t. Some boilers have filling loops and some have internal filling keys, it’s the same principle to repressurise but slightly different methods are used.

  • Switch off your boiler and let it cool completely
  • Find the filling loop (flexible silver cable) and make sure both ends are tight or you may have an internal filling key but it’s the same principle.
  • Open bath valves or turn your internal filling key to allow cold water into the system, this will repressurise the system.
  • When the gauge reaches 1.5 bar close both valves.
  • Remove the filling loop if it isn’t a permanent attachment.
  • Turn the boiler back on.
  • Check in a few days to see if it has lost pressure again.

If you continually lose pressure then there is likely to be a leak in your system that you will need to identify and resolve to ensure you stop losing pressure.

How can I fix a radiator valve leak?

Another common reason for a boiler losing pressure is caused by a leaking radiator valve. Check all of your radiators to see if you can spot any water on the floor around your valves. Your heating will need to be on for the leak to occur so repressurise your system first. Even a small leak from a radiator over time will decrease the pressure in your system and cause your boiler to switch off and display an error code for low pressure.

If you spot a leak on a radiator valve then you can either drain down your system and replace the valve if you feel comfortable or, you can call out a plumber to do it for you. It’s a routine job and won’t cost too much (depending on the plumber!). If you’re very lucky then the leak will be coming from a gland nut, which can just be tightened and this will resolve the issue.

Some leaks can be fixed by unscrewing your gland nut slightly and winding some PTFE tape around the affected area, this can help close the gap where water is escaping from.

How can I fix a system leak?

If you have checked your system and can’t find any signs of a leak then you may have a pinhole leak somewhere you can’t get to. Some companies recommend using a leak sealant, but this is the equivalent of sticking a plaster on a cut, it will come off eventually and unlike us, your leak won’t heal, so you’ll be back to square one.

Leak sealants can also make it more difficult to locate the leak if you call someone in to fix it and it can also void the warranty on your boiler. It can work as a temporary fix but you’re better off getting the underlying issue sorted. 

Sometimes a leak can be fixed with a little soldering, over time and movement leaks can occur from wear and tear, especially on pipe bends. Generally, we recommend calling out a plumber or a Gas Safe engineer if you have a leak in your system.

How can I fix a leak from the boiler?

As discussed above, we don’t recommend you fix a leak that’s coming from your boiler as you shouldn’t be taking the cover off unless you’re a Gas Safe registered engineer.

If you think you have a leak coming from your boiler then we recommend acting swiftly as it can cause further damage to your system.

Possible issues that can cause a leak to come from your boiler include damaged or broken seals. Over time seals will degrade and fail, this is an inexpensive fix.

An expensive outlay is the expansion vessel. If the boiler pressure gets too high the expansion vessel acts as a buffer, if it fails, then the pressure is forced elsewhere and can cause leaks in doing so.

A cheaper problem to fix can be a pump working itself loose. Over time your water pump will move around and this can cause leaks.

A crack in your heat exchanger is another common cause of a leak from within your boiler. If your boiler is still within warranty then now is the time to call the manufacturer and get an appointment for them to come and take a look.

If your boiler is out of warranty, you need to weigh up whether it’s worth spending a few hundred pounds getting the heat exchanger replaced.

Is it worth the cost of fixing my boiler?

If your boiler is over ten years old then rather than spending money on fixing issues you may be better off putting the money toward a new boiler. It can get very expensive fixing a failing boiler, as well as the inconvenience of organising heating engineers to come round all the time, all those cups of tea for the engineer too…

If your boiler is getting on in years then it may be difficult to source replacement parts, meaning that the prices will go up and the repairs will take longer as heating engineers wait for parts to be delivered.

It only takes a couple of expensive jobs and you will have shelled out a substantial amount that could have gone toward the cost of a new boiler. WarmZilla boiler prices start from £1499 and boiler finance options are available to spread the monthly cost of your boiler to an affordable amount. We understand it’s a difficult decision whether to repair or replace your old boiler and every situation is different, just make sure you don’t sink too much of your hard-earned money into a boiler that’s on its way out.

If you’re ready to start thinking about buying a new boiler, then we have you covered with our comprehensive review of the ‘Best Boilers in 2021’. You can also get an online fixed price quote from WarmZilla in 60 seconds by taking our survey now.

If your boiler is less than five years old and hasn’t had many issues previously, it’s probably in your interest to get whatever issue it has fixed. If it’s older than ten years and out of warranty, then it may be time to start looking at replacing your old boiler.

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