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Witten by Bernard Morgan (Engineer) & Adam Apperley (Marketing).
Published: July 11, 2019. Updated: February 19, 2024

What is a Diverter Valve and how do they work?

A Diverter Valve opens and closes to direct the flow of hot water to your taps or central heating.

This is the simple explanation, but you may very well have more questions to ask such as:

  • What does a diverter valve look like?
  • Common diverter valve problems?
  • What should I do if I find a faulty diverter valve?
  • How much does a diverter valve cost?
  • When wouldn’t I need to replace my diverter valve?

You might need to replace your diverter valve if you’re not able to get your hot water or heating supply working independently. You’ll find that a combi boiler problem such as this can be more frequent is your boiler is getting old.

Perhaps you’ve heard your friends and family talk about diverter valves before. This is why it’s important to know what you’re buying. Diverter valves are only found in combi boilers, whereas other types would require an external valve. But if you want to learn more about this part of your combi boiler, you’ve come to the right place!

Let’s see what else there is to know about diverter valves!

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What does a diverter valve look like?

what does a radiator valve look like

Diverter valves can vary in appearance, but the one pictured above is used by the German manufacturer Viessmann – a leading example in today’s industry. Other brands out there have their own designs that serve the same purpose, but with varying levels of success and quality.

Third-party diverter valve manufacturers, such as Giannoni, design their components and repair kits to be used across multiple brands. Below, you can see a collection of diverter valves from different manufacturers. Notice the difference in materials for each component. Some diverter valves use plastic, which can often cause problems in the long run due to material degradation. 

Ideal diverter valve

Ideal Diverter Valve


Baxi Diverter Valve


Baxi Diverter Valve

Worcester Bosch Diverter Valve


Vaillant Diverter Valve

Vaillant Diverter Valve

What does a diverter valve do?

Diverter valves open or close to direct hot water to the radiators or taps and showers. If you have your central heating on, try turning on the tap. When this happens, the diverter valve will close off the central heating supply and divert it to the taps instead.

This is essentially how diverter valves work. They respond by redirecting the water to the appropriate outlet, whether it’s central heating or out the taps and shower. If the water is supplied to the heating system, it’ll reach the boiler’s primary heat exchanger. If it’s for your hot water supply, it will be directed to the plate heat exchanger to warm the water for your taps and showers.

Inox-Radial Stainless steel heat exchanger

Viessmann’s primary Inox-Radial Stainless steel heat exchanger


Viessmann plate heat exchanger

Viessmann plate heat exchanger

If you’re worried about your hot water coming from the same supply as the central heating, worry not – separating this water is exactly what the diverter valve can prevent.

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Common Diverter Valve Problems

Every component inside a boiler can degrade over time, including the diverter valves. These get used a lot because hot water and heating are regularly called for – even more so during the winter. Diverter valves vary in style and quality depending on the manufacturer, but as long as you pick the right one, you can enjoy extended lifespans on all components.

Here, you can find common issues that many homeowners have come across with their diverter valves:

Lukewarm Water

If the water coming out of your taps and showers is only lukewarm, you may have an issue with your diverter valve.

This is one of the more common symptoms to experience if you’re having trouble. More often than not, it will happen because the valve itself is getting stuck. When it gets stuck, it might be left slightly open on the heating side, which means hot water normally going to the taps and showers is otherwise lost.

When this happens, consider how your annual energy bills may be affected. The more heat that gets lost, the more money is wasted. Because combi boilers have excellent efficiency all-round, you’ll want to enjoy the benefit by getting this sorted out as soon as possible.

Hot water but no heating

The cause for this is similar to the ‘lukewarm water’ scenario. The diverter valve will probably be stuck on the side supplying hot water. Because of this, if you turn your taps on, the valve won’t be able to provide you with the hot water you need. It will only be able to send the water through to central heating.

No hot water

You may find you are unable to get hot water to come out your taps. Try seeing what happens when you turn your central heating on as well. If it’s only now that you get hot water coming through the tap, you’ll probably have a problem with your diverter valve.

A faulty diverter valve can have numerous effects on your boiler’s components. It can cause a buildup of limescale in your domestic hot water supply and magnetic sludge in the water going through your central heating system. This makes your radiator cold at the bottom, which requires a chemical flush or similar process to clear out.

How old does your boiler need to be to consider replacing?

If your boiler is reaching a decade old, a faulty diverter valve might not be the only problem. Even if it’s a small repair, it can be challenging to predict how much longer it will last. You could spend anything from £150 to £500 for any basic repair. When talking about prices of that size for a boiler repair, you have to ask yourself: Is it really worth it?

Consider the possibility that getting a new boiler might be the better option if you don’t want to spend hundreds of pounds on a new part.

What you need to do next

If you’ve encountered any of these issues, you’re probably already looking to get them sorted. After all, you’re reading this blog right now!

The first thing you should do is seek professional advice on how to solve the problem. Whether this is done through an installer like Boilerhut or an independent contractor, they can provide more detailed answers.

However, you don’t want to have just anyone try to service your boiler. If someone unqualified tries this, it can have serious repercussions. Not only is it against the law, but it may also affect the warranty and home insurance. In scenarios such as this, you need to ensure your boiler can last a long time, therefore it’s unwise to involve anyone who isn’t qualified.

Free advice and quote

Because Boilerhut is an approved Viessmann installer, we can offer detailed and reliable advice for you, your boiler and all of its parts free of charge. If you want to replace your old boiler entirely, we’re happy to discuss your situation.

Call Boilerhut on 029 2009 9898 where we can discuss exactly what the best option is for you. You can also get a free, no-obligation quote by filling in your postcode below.

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How much does a new diverter valve cost?

Prices for diverter valves can vary quite a lot.

Avoid buying a cheap product and instead make sure your old boiler uses components that are built to last.

Take a quick look on google. An average price for a diverter valve can be around £200+ with many manufacturers charging a lot more money, which only covers the price of the part itself. You also need to consider the cost of labour as well, which means the price could rise even more than expected.

Based on our repairs on older boilers, the cost on average will be between £400-£800. Multiple visits could be incurred if further faults are found. More components would need to be replacing, costing you even more money.

As well as the diverter valve, your problem may also be related to the boiler’s diaphragm. When you open your hot water supply, the diaphragm moves in response to the pressure difference to help divert the water. If your boiler is quite old with worn-down components, a part like the diaphragm can be punctured. When this occurs, the boiler won’t be able to switch easily between the water supply for the taps and the central heating.

If you’re put off paying so much for just one component to your boiler, be wary that there’s always a chance something else could be failing as well if it’s too old. If your boiler is approaching ten years old or above, a replacement boiler might be the best option for you.

What’s to consider if you’re thinking of having a repair

Besides the cost, there are other factors that you’ll need to take into account as well.

  • Callout charges will apply – normally between £50-£150 based on location and company size
  • A typical component repair or replacement like this can usually take between 2-4 hours to complete
  • Labour costs vary depending on where you are in the country and company size. For example, local installers in London are able to charge a lot more compared to somewhere further out and remote

Each manufacturer makes their boiler differently, and so the ease of replacement can change depending on which ones you’re dealing with.

With all this considered, you may want to seriously reconsider spending hundreds of pounds on a boiler with no warranty. Components could fail over time and without the right protection, you can find yourself stuck.

From our own experience, Boilerhut has seen clients go through such problems, ultimately deciding that buying a new boiler that doesn’t constantly fail is the best option. If you’re after more information on this, you can do the same yourself and get a free, no-obligation quote by entering your postcode below.

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Save up to £590 PER YEAR on your heating bills.
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Get the right advice

At times like this, it’s always important to get the best advice possible. Speak to friends and family, but be sure to get professional support to thoroughly check the boiler and its parts as well.

Be mindful of your current warranty as well. If it’s reaching the end of it’s lifespan, getting a new boiler may very well be your best option. Read one of the following blog posts to find out more about the costs that come with a new boiler:

Do you need a new boiler? Is yours beyond economical repair?

If you need a new or replacement boiler, get an online quote (it takes less than 1 minute), and you’ll get an instant price. But why choose Boilerhut:

  • Next day boiler installation.
  • Instant, no-obligation quote in less than 1 minute.
  • Finance options available for new boilers and central heating installation.
  • 10 to 12-year warranty on boilers.
  • ‘Excellent’ 5* customer satisfaction on Trustpilot.
  • Fixed prices. No hidden extras.
  • Get up to three quotes for different-tier boilers.

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