How to Bleed a Boiler and Other Common Tips & Fixes

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 to inspect your boiler.

How to Bleed a Gas Boiler?

radiator blue right

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

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. Make sure your boiler has been turned off for at least an hour to reduce the risk of scalding.
  2. Insert a radiator key into the valve on the radiator and turn very slowly, with a basin underneath to catch drips.
  3. You must turn the key slowly as the pressure in the system will cause the water to come shooting out otherwise.
  4. You’ll hear the air hissing out, and as soon as some water appears you should close the valve immediately.

Bleeding your gas boiler is that 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 can you know if you have air in your boiler system?

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 to Bleed an Oil Boiler?

gas boiler orange

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. Take the cover off at the bottom of the boiler.
  2. Remove the bleed nut, you’ll usually need an Allen key or a spanner to do so.
  3. Run the boiler until fuel runs out, clear of air.
  4. Replace the nut.
  5. Your boiler should now function properly.

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.

My Boiler is Not Firing Up?

chubby man thinking left

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:

  • If the thermostat is set too low, the boiler will not come on until the room temperature is lower than the temperature the thermostat is set to. Simply increase the temperature on your room thermostat.
  • Also, check where your thermostat is placed. If it is near any heat-generating appliances or in direct sunlight, it will be registering a higher temperature than the actual house temperature.
  • Turn the thermostat up to its highest setting, and if the boiler comes on, then the most likely culprit is the thermostat 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.

How to Check the Boiler Pressure?

A grey pipe with a pressure gauge attached

Is 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.

Common Boiler Noises

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.

    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.

  2. Clunking or 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.

Other Boiler Maintenance

handywoman spanner left

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, repressurizing your system, or thawing a condensate pipe, do not attempt any DIY 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.

Boiler Service & 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, 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.

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, and cost you more money than it’s worth. If that’s the case then you should consider getting a new one sooner. 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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