With fuel bills going through the roof, your central heating system must run properly and efficiently. It doesn’t matter if you have designer radiators or any kind of radiator, if they are not in good working order, your system will have to work harder to produce the same effect, and this will have a knock-on increase in your fuel use. Just like your car engine runs more efficiently the better it’s maintained, and so will your central heating. The best time of year to do all the maintenance jobs is in the summer when you’re not using your central heating at all.

The additional advantage of doing all the radiator maintenance jobs in the summer is that if you discover something that needs repairing or replacing, you can schedule the work at a time that suits you, rather than paying for emergency repairs.

Here are the jobs you need to be thinking about doing over the summer:

Boiler service

If you don’t already get your boiler serviced annually, you need to start! A service will ensure your heating system is working as efficiently as possible and will hopefully pick up anything now that might cause problems later when the weather gets cold. Make sure you choose an engineer who is Gas Safe registered. If you are unsure what a boiler service involves, the consumer association Which? has published a handy checklist of what your engineer needs to look at.

Bleeding radiators

Sometimes, if air gets trapped in the system, a radiator may not heat up evenly – you might even hear gurgling sounds when you turn the heating on. If this is the case, you need to bleed your radiators, which is a simple and straightforward process.

Do any radiators need bleeding?

To check your radiators, you’ll first need to turn the heating on. Once it’s up to temperature, run your hand over each radiator from top to bottom. If there is any air trapped, the radiator will be noticeably cooler towards the top.

Bleed any radiator with a cool spot

Before you start, be sure that the heating is now switched off and wait until the radiators have fully cooled down. The valve that you need to open is located at the top of the radiator at one end. The bleed valve has a squared-off middle which fits a radiator key. If you don’t have a key, you can buy them from any DIY or hardware shop. On a modern radiator, you can use a flat-bladed screwdriver by placing the end into the groove in the centre of the valve.

Use an old cloth to catch any drips and turn the key or screwdriver anticlockwise – do so slowly, a quarter turn should be enough. You will hear a hissing noise when the trapped air is being released. Be ready to close the valve quickly as soon as the hissing stops and liquid starts to emerge through the valve.
An important thing to do is check the colour of the water coming out of the radiator – if it’s anything other than clear, then you may have a build-up of sludge in your system (see Flushing below).

What to check afterwards

Check the pressure gauge on your boiler to see if you need to increase the pressure level. This should be sitting at between 1.5 and 2 bars when cold. When you turn the heating back on, the radiator should be warm all over.


If your radiators still have cold spots after you’ve bled them, particularly if those cold spots are at the bottom, it could be a sign that the system needs flushing. What happens is, over time, rust and dirt – a.k.a. sludge – will accumulate in your radiators and pipes, which can block the flow of your central heating. The resulting inefficiencies will cause your heating system to have to work harder to heat your home, costing you more money. If you don’t sort the problem out, it could eventually end up damaging the entire system. So if you think there may be sludge in your radiators, book a plumber in to flush the system sooner rather than later!

Signs of sludge building up

There are some signs to look out for to assess if it’s time to flush the system, starting with the colour of the water when you bleed the radiators. If it’s clear, you’re OK. If it’s slightly brown, then you’ve got sludge in the system, and you therefore need to get it flushed. If the water is very dark brown, then you’ve got a major problem with sludge and need to get it flushed as soon as possible.

Other signs are when radiators take a lot longer to heat up or there are cold spots on them. If you find yourself needing to bleed the radiators more often, or your boiler becomes very noisy, these are also indicators that sludge may be causing problems.

Preventing sludge build-up

You can now take measures to prevent sludge building up in your central heating system, which will protect your system and save money on flushing it. A magnetic boiler filter will collect the sludge and allow you to remove it easily and cheaply. Filters cost less than £100 and are relatively straightforward to install. They only need cleaning once a year, so if you don’t fancy doing it yourself, you could ask the plumber to add the job to your annual boiler service.