What is a Diverter Valve and how do they work?

What does a diverter 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.

There are also third party diverter valve manufacturers such as Giannoni that 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

Baxi Diverter Valve

Worcester Bosch Diverter Valve

Vaillant Diverter Valve

What does a diverter valve do?

Diverter valves work by opening or closing 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 closes 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 being supplied to the heating system, it’ll be reaching the boiler’s primary heat exchanger. If it’s for your hot water supply, then it will be directed to the plate heat exchanger to warm the water for your taps and showers.

Viessmann’s primary Inox-Radial Stainless steel 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.

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 is 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 of the components.

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

Lukewarm Water

If the water that’s coming out 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 does get stuck, it might be left slightly open on the heating side, which means hot water that should normally go 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

None of us should have feel this cold!

The cause for this is similar to the ‘lukewarm water’ scenario. The diverter valve itself will probably be stuck on the side that supplies 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’re 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 affects on your boiler’s components. For your domestic hot water supply, it can cause a build up of limescale. For the water going through your central heating system this causes a build up of magnetic sludge. This makes your radiator cold at the bottom, which requires a chemical flush or similar process to clear out.

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 difficult to predict how much longer it would last. For any basic repair, you could spend anything from £150 to £500 pounds. When you’re talking about prices of that size for a boiler repair, you have to ask yourself: Is it really worth it?

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

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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.

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