How To Bleed Your Boiler: Our Guide for Boiler Maintenance

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A man holding a blue box and several tools inside it walking towards a winter boiler

In Ireland, boilers are quite costly and essential to many households. Safety risks can arise when they malfunction from a lack of maintenance and boiler repair is also no joke when it comes to financing. This is why we provide you with an easy guide to bleed your boiler and help you stay on the ball with our boiler maintenance tips and quick fixes - as well as knowing when to call in a professional.

Switch your boiler off IMMEDIATELY if any of the following situations applies! 🔴 You smell gas or fumes
🔴 If you see any scorch marks or soot on or around your boiler.
🔴 The pilot light keeps going out or the flame is yellow (a sign the boiler can’t draw in fresh air).
🔴 You get a headache or nausea if you’re in the vicinity of the boiler when it is running (which could be a sign of carbon monoxide poisoning).

Once your boiler is switched off, call a Registered Gas Installer of Ireland (RGII) to inspect your boiler.

Why Should I Bleed a Gas Boiler?

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Any heating system with air trapped inside works less efficiently, meaning you’ll end up paying more on your energy bill for less heat.

Bleeding your gas boiler is simple and can save you a significant amount on your heating bill this winter! If you don’t have a radiator key, you can buy one at any hardware store, such as Woodies. In a pinch, you could also use a screwdriver but you may damage the valve and make it harder to bleed them in the future.

How Do I Bleed a Gas Boiler?

For gas boilers, which are connected to your radiators, the solution is to bleed your radiators to remove air from the closed circuit heating system. Here are the quick easy steps to bleed your gas boiler:

  1. Turn Off Your Boiler
    Ensure your boiler is off and has cooled down for at least an hour before starting. This step is crucial to avoid the risk of scalding from hot water or steam.
  2. Insert a Radiator Key
    Locate the valve on your radiator and carefully insert a radiator key. Position a basin or cloth underneath to catch any drips that may occur during the process.
  3. Turn the Key Slowly
    Gently turn the key clockwise, being cautious to do it slowly. This prevents the pressurized water from ejecting rapidly and creating a mess or causing injury.
  4. Close Valve After Seeing Water
    Listen for the hissing sound of air escaping. As soon as water starts to dribble out, promptly close the valve. This indicates that the air has been successfully bled from the radiator.

How Can Do I Know There's Air in My Boiler?

If your radiators are making gurgling noises and are heating up at the bottom but are colder at the top, this is a good indicator that you either need to bleed them or even purge the system with a power flush (to remove sludge).

Boiler PressureAlways check the pressure in the system via the display on your boiler after bleeding your radiators, and top up if necessary.

How Do I Bleed an Oil Boiler?

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If you’ve been unlucky enough to run out of oil while waiting for a delivery, you’ll need to flush out the air in order to get your oil boiler started again. While you should always refer to the manufacturer's instructions for your particular type of boiler, in general, the following holds true to bleed most oil boilers:

  1. Remove the Boiler Cover
    Begin by carefully taking off the cover located at the bottom of the boiler. This provides access to the internal components necessary for the bleeding process.
  2. Remove the Bleed Nut
    Identify the bleed nut, which is usually found on the burner's pump. Use an Allen key or a spanner to loosen and remove this nut. Ensure you have the correct tool for your specific boiler model.
  3. Run the Boiler and Bleed
    Switch on the boiler and allow it to run. Watch for the fuel to start flowing out of the bleed nut's opening. This indicates that air is being expelled from the system. Continue this process until there is a consistent flow of fuel without any air bubbles, indicating that the air has been cleared.
  4. Replace the Nut and Test
    Once the fuel flows steadily without air, turn off the boiler and carefully replace the bleed nut, ensuring it is securely tightened. Restart your boiler to check if it functions properly. The boiler should now operate smoothly without air blockages.

If in doubt about which bung you should remove, and you can’t find the instructions, then consider asking the oil delivery person to help you. They will normally do so for free.

How Do I Check the Boiler Pressure When Bleeding?

When bleeding your boilers, it's important to check if your boiler pressure too high or too low. At a minimum, pressure should be at 1 bar, with 1.5 bars being optimal (do check the manufacturer’s guide to make sure). If your boiler pressure is too high, it’s normally an easy fix. If you have recently repressurised your system, it may be that you didn’t close the pressure valve properly.

Check to make sure it is tightly closed. To reduce the pressure, bleed your radiators. However, if this doesn’t work, you’ll need to call in the professionals. If your boiler pressure is too low, gently open the pressure valve until the pressure is between 1 and 1.5 bars. Again, if this doesn’t work, then you’ll need to call a qualified engineer.

What Common Boiler Noises To Watch Out For?

Here are some common boiler noises you may come across and how to quickly fix these issues yourself:

  1. Gurgling or Whistling Noises
    These may be caused by air in the system or a frozen condensate pipe. If you suspect air in the system, then you will need to bleed your boiler.
  2. What If I Have a Frozen Pipe?
    If you suspect a frozen pipe, verify if your pipe is outside and easily accessible. If so, you can thaw the pipe yourself with a hot water bottle or heat wraps. If this was the cause of the issue, definitely consider lagging your external piping to prevent it from occurring again.Clunking or
  3. Banging Noises
    Often caused by something called 'kettling'. Kettling is a build-up of pressure in the system, normally caused by an accumulation of limescale deposits restricting water to the heat exchanger. Kettling can cause serious damage to your boiler, so if you think this may be the issue then call an RGI professional straight away to scrub out your heat exchanger.

Exercise for Your Boiler in the Summer! Normally as soon as the warmer weather comes calling, we forget all about our heating systems and focus on our cooling system! However, your boiler will still need some TLC during the warmer months. To keep it fighting fit and ready for winter, turn it on for five-ten minutes with the thermostat up high every few weeks. This will prevent sludge and dirt from accumulating inside, and save you from having to get an engineer to power flush the system in winter.

What Other Boiler Maintenance Is Needed?

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Faulty boilers are usually safe, especially if they are more modern ones. This is because modern boilers come with built-in safety precautions which will prevent them from operating if a fault develops. Always perform a quick visual inspection of your boiler regularly to stave off issues.

Look out for leaks and fault messages. Also, listen for banging or gurgling and keep the space around your boiler clear. We’ve rounded up some general maintenance tips above, how to solve minor boiler issues, and how to spot potentially dangerous boiler-related situations.

No DIY Boiler Repairs! Aside from bleeding your radiators, repressurising your system, or thawing a condensate pipe, do not attempt any DIY gas boiler repairs. Never open up your boiler - this is incredibly dangerous. It will also void any warranty, and may also void your home insurance cover. Only trained and registered boiler technicians should attempt a repair.

Why Is My Boiler Not Firing Up?

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If your boiler is working and producing hot water, but not firing up when you put the central heating on, then chances are it could be an issue with your thermostat. Here are some common fixes regarding boilers which do not start due to the thermostat:

  1. Adjust the Thermostat Setting
    If the thermostat is set too low, the boiler won't activate until the room temperature drops below the thermostat setting. Simply increase the temperature on your room thermostat for a quick fix.
  2. Evaluate Thermostat Placement
    Check the location of your thermostat. If it's near heat sources or in direct sunlight, it may register a higher temperature than the actual room temperature, affecting boiler operation.
  3. Test with Maximum Thermostat Setting
    Turn the thermostat to its highest setting. If the boiler activates, then the thermostat is likely at fault. This test helps confirm if the issue is with the thermostat rather than the boiler itself.

Thankfully, thermostats are much cheaper to replace than boilers. If you do need to replace your thermostat, then consider getting a smart thermostat or a thermostat with a timer, in order to reduce energy waste.

Why Should I Get Boiler Service or Cover?

handyman holding spanner left

Having your boiler serviced regularly can save up to 15% on fuel costs and keep your boiler running in tip-top condition. Boiler parts are also extremely expensive and in some cases, you may be better off buying a new one than salvaging your current one. Definitely have your boiler regularly serviced (at least once every 12 months), and consider taking boiler cover out, such as Bord Gáis Boiler Service cover, especially if your boiler is on the older side.

Boiler cover will generally cover parts replacement (up to a certain amount), emergencies, callout service, and maintenance. When an RGI is called out to your house, they will also check for proper ventilation and whether the flue has degraded. Another sensible addition to your household would be a carbon monoxide detector near your boiler, just in case. It should also be noted the gas boiler replacements in Ireland will get much rarer due to Ireland's green energy commitments.

When Should You Buy a New Boiler?

Boilers should last up to 15 years. However, if your boiler is more than 8 years old, then it may be much less efficient than the new condensing boilers or electric boilers, and cost you more money than it’s worth. If that’s the case then you should consider getting a new one sooner. Unfortunately, you can no longer get boiler grants in Ireland but the investment is still worth it.

Older gas and oil boilers only convert 77% of fuel to energy, compared to 91% with a newer condensing boiler, an obvious efficiency gain. Our personal favourite for single households and smaller families is a combi boiler (with condensing function). Have a look at our different boiler guides evaluating the pros and cons of every boiler type available in Ireland.

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