In the current heatwave, you probably won’t be thinking about radiators at all, but this is actually the best time of year to do all those maintenance jobs to ensure your central heating system works effectively when you’ll really need it.

Boiler service

If you don’t already get your boiler serviced annually, you need to start! A service will ensure that 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.

Bleed your 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?

If you want to check your radiators, you will 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 air trapped, the radiator will be noticeably cooler towards the top.

Bleed each radiator with a cool spot

Before you start, be sure that the heating is now switched off. The valve that you need to open is located near the top end of a radiator. It has a squared off middle which fits inside a radiator key. If you don’t have a key, you can buy them from any DIY or hardware shop. Or contact us at The Radiator Centre and we’ll send you one. 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 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 buildup 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 to 2 bar 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 they’re at the bottom, it could be that the system needs flushing. What happens is that, 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 in order 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 it’s time to get the plumber in!

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; when there are cold spots on the radiators; you find yourself bleeding the radiators more often; or your boiler has become very noisy.

Preventing sludge build up

You can now take measures to prevent the build up of sludge 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 on to the annual boiler service.