Why is my radiator making a hissing noise?

Usually, these hissing noises aren’t anything to worry about—but it's still a good idea to keep on top of them. In this guide, we’re going to look at how you can fix those hissing noises before they develop into anything too serious.

Why is my radiator hissing?

Hissing noises usually come from water moving through your heating system, which creates noise as it passes through valves and fittings.

So, for example, if your radiator begins to hiss when you turn it on but stops once it's heated up—it just means that water is travelling through your pipes to feed the radiator. This is quite normal and usually nothing to worry about.

However, if you hear hissing sounds that are followed by banging, thumping, gurgling or other louder noises, then this is something a qualified heating engineer should check.

How to stop a hissing radiator

To reiterate, hissing noises aren’t always a sign of a problem. Still, it’s definitely a good idea to take a look into it, especially if you notice the hissing getting louder.

The first thing you should do is locate where in your house the hissing radiators are. If the hissing isn’t coming from a radiator, it could be coming from the pipes to and from the radiators, which possibly indicates a leak.

If you encounter a hissing noise coming from the boiler, then you should get a heating engineer to take a look as soon as possible.

How to stop a radiator hissing in five simple steps

1. Check the thermostatic and lockshield valve

If you have recently:

• had a new radiator and valves fitted
• removed your radiator for decorating

...or are just experiencing a hissing noise from your radiator, it could be due to the water flowing through your thermostatic or lockshield radiator valve.

To fix the issue, try adjusting the thermostatic radiator valve by turning it up or down. If doing so alters the noise, it may be that the water has simply been restricted by the normal operation of the valve. If that’s the case, this noise is nothing to worry about.

If turning your thermostatic radiator up or down fails, use a spanner and adjust the lockshield by 1/4 of a turn (anti-clockwise) only. Turning the valve further may alter the balancing of the system. If neither of these work, then it would be best to call a heating engineer.

2. Bleed the radiator and close the bleed valve

If you’ve bled your radiator then it could be that you’ve not tightened the bleed valve properly. Alternatively, it could even be that the valve has come loose. Either way, if the air vent is open it’ll mean that air or water will be escaping.

Make sure to bleed your radiators around once a year to keep them running smoothly!

3. Excess air in the system

If you find that you’re having to bleed your radiators quite often, or the hissing or gurgling noises aren’t stopping, then this could mean that your heating system is full of air from somewhere.

This could suggest there’s a potential problem with your radiators or plumbing, which will need to be looked at by a qualified engineer.

4. Patch pinhole leaks caused by limescale hotspots

The hissing noise you can hear could even be coming from the radiator leak itself. This is more likely to happen in older radiators and heating systems.

These leaks can be difficult to detect as they’re really small, but the cause is usually from limescale hotspots and internal corrosion.

As a temporary solution, you can patch and fill the hole, but eventually, you will have to replace your radiator. This is probably the more cost-effective answer in the long run.

Make sure to have a chat with your heating engineer to find out what caused the leak and how to stop it from happening in the future.

5. Balance the radiators

Hissing noises can sometimes be related to an imbalance, which can mean that your radiators are slow to heat up, or in some cases don’t heat up at all. 

You can resolve this issue by rebalancing your radiators. Or if they continue to be cold, then you may want to check out our guide on how to fix a cold radiator.

Is a hissing radiator dangerous?

In most cases, hissing noises coming from your radiators usually aren’t dangerous.

While hissing noises might give the impression that there is an imminent fault, if the radiator is just making a hissing noise it’s unlikely that this is dangerous for your home.

Keep your radiators running smoothly with HomeServe

Keep having to deal with problems with your radiators? It’s worth considering the use of our one-off repairs service so one of our qualified engineers can come out to resolve the issue for you.

Looking for a longer term solution? To keep your home, heating, and radiators themselves covered in case of unexpected problems, take a look at our range of heating and boiler cover.