Vasco Zana Vertical Designer Radiator finished in textured white in living space with wicker chair

Radiator flow diverters explained: better heat, fewer cold spots

Written by
Nick Duggan

Radiator flow diverters might not be the first thing you think about when choosing a vertical radiator, but they can make a world of difference to how warm your room feels.

Vertical radiators have become a popular choice for modern homes. With open-plan living on the rise and furniture getting bigger, wall space is at a premium – and tall, slimline radiators are an attractive way to heat a room without sacrificing style.

If your radiator doesn’t have a flow diverter, it might not spread heat as evenly as you’d expect. Instead of filling with warmth top to bottom, it could leave you with cold spots where you least want them. A diverter ensures even heat from top to bottom, so your radiator does its job properly and your room stays comfortably cosy.

Cordivari Rosy Max high heat output Radiator in F22 Classic Gold

What is a flow diverter – and why does it matter?

A flow diverter is a simple internal screen fitted inside a vertical radiator. It changes how hot water moves through the radiator, forcing it upwards first before it flows down and exits.

Without a flow diverter, hot water often takes the quickest route – skimming straight along the bottom tubes and leaving the top of the radiator cold. That means your radiator isn’t giving out the heat it’s designed to, and your room can end up feeling cooler than expected.

With a flow diverter, water spreads evenly through the entire radiator. This helps:

Ensure your radiator performs to its stated heat output
Warm up your room more quickly
Keep running costs down, as your boiler won’t need to work as hard
Reduce fuel use and emissions by improving heating efficiency

It’s a small addition – but one that can make a big difference to your comfort and energy bills.

How do I know if I need a flow diverter?

If the top of your radiator feels cool, even after you’ve bled it, or your room just isn’t warming up as expected despite the radiator having a high BTU rating, it could be down to one thing: no flow diverter. You might also notice the sound of water rushing through the valves when your heating is on.

These are tell-tale signs that hot water isn’t reaching the top of your radiator. It’s common in tall radiators – especially ones over 1500mm high and installed with BOE (bottom opposite end) pipework.

Not all radiators come with a diverter as standard, so it’s worth checking before you buy to make sure the style you’ve gone for will heat your space properly.

Milky White Tuba vertical radiator shown in bedroom with putty colour walls

How to check if you’ve got a flow diverter

First, make sure you’ve bled the radiator to get rid of any trapped air. Then, when the heating is on, run your hand from the bottom to the top. If the top feels noticeably cooler, it could mean there’s no diverter.

Another way to check is by gently inserting a stick or dowel into the bottom tube. If it hits a blockage partway across, that’s usually the diverter in place.

You can also check the product specs or ask your supplier directly. And if you discover your radiator doesn’t have a diverter, don’t worry – in many cases, it’s possible to add one afterwards. If you’re unsure, our team’s always happy to help and advise.

What else could cause cold spots?

Cold spots aren’t always down to a missing flow diverter. Sometimes, it’s as simple as the radiator needing a proper bleed to get rid of trapped air. Other times, the radiator might be too small for the room – if the BTU is too low, it just won’t keep the space warm. To check how much heat your room probably needs, use our simple Heat Calculator.

Another common issue is the heating system not being properly balanced, meaning the heat isn’t being distributed evenly around your home.

While a diverter won’t fix these problems on its own, it’s often the missing piece that makes a big difference to how well your vertical radiator performs.

Why it’s worth getting right

Adding a flow diverter isn’t just a technical detail. It means your radiator heats up faster, spreads warmth evenly, and helps your boiler work more efficiently. You’ll use less energy, lower your bills, and enjoy a cosier, more comfortable room.

It might be a small component – but it can make a big difference to how your home feels.

Confused about flow diverters?

If you’re not sure whether your radiator needs one – or want advice on choosing the right model vertical radiator for your space – our team is here to help. Pop into a showroom, give us a call, or drop us a message and chat to our team.