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What is a Diverter Valve?

Becky Mckay
By: Becky Mckay
Updated: 9th October 2023

Diverter valves are part of heating systems with a combi boiler.

They direct water heated by the boiler to either the radiators or hot water taps. Depending on which you want at the time. This means that if it gets stuck then you’ll only get one or the other.

What is a diverter valve?

Boiler diverter valves send hot water to either the radiators or the domestic hot water system (taps and showers).

If you have a bath with an overhead shower then you’ll already be familiar with this system. Every time you want a shower, rather than a bath, you’ll need to move the tap diverter.

Does my boiler have a diverter valve

If you have a combi boiler then it will have a diverter valve.

System and regular boilers don’t have a diverter valve. This is because they store domestic hot water in a cylinder rather than sending it straight to the taps.

How diverter valves work

Diverter valves give priority to the hot water for your taps over the heating. So if you've got the heating on and fancy a warm shower, you'll be given priority over the radiators.

How to spot a diverter valve fault

As a moving part, the diverter valve can get stuck. This is a problem often suffered by older boilers.

Should you be experiencing any of the following, then there might be a fault with the diverter valve in your boiler:

  • You have to turn the heating on to get hot water
  • There’s plenty of hot water but no heating
  • You only get lukewarm water from hot tap

If you're finding that you have one of the above issues with your central heating and hot water, we've listed what causes the common diverter valve problems below.

Common diverter valve problems

Diverter valves are an important part of combi boilers. So an issue could affect the heating and hot water all around your home.

As a moving part, the most common faults are caused by it getting stuck.

No hot water

Should the water from the hot tap not be warming up, try turning the heating on to see if this does the trick. If you find that the water starts turning hot then it's highly likely that there's a fault with the diverter valve.

Hot water but no heating

A likely cause is that the diverter valve has stuck. This means that hot water will be sent to the taps but your heating won't warm up.

Lukewarm water

A stuck diverter valve can also mean that you end up with lukewarm water from your taps. This happens when the diverter valve is slightly stuck open on the heating side. Some of the heat that should be going to the hot water for the taps will be lost.

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Diverter valve costs

When having a new Combi boiler installed, it will have a diverter valve fitted as standard. However, should it need replacing you'll need to buy a new one.

The diverter valve itself will likely cost around £75 – £200 but this doesn't include the cost of installation which will vary depending on the engineer carrying out the work.

The engineer will recommend the best type of diverter valve for your system but if you do want to shop around and find one that meets your budget then you'll need to know what you're looking for. There are many different models of Combi boiler meaning that there isn't a 'one size fits all' diverter valve so you'll need the right size for the Combi boiler installed in your home.

You'll come across various models, many of which will provide either heating or hot water, however, a mid-position diverter valve allows you to have heating, hot water and both. They tend to be more expensive but being able to use hot water and keep your radiators warming up is well worth the extra investment.

Popular diverter valve models

Take a look at some of the most popular models of diverter valve on the market and how much they could cost.

Diverter Valve Sizes Potential Cost
Honeywell 2 Port Zone Valve 22mm and 28mm £85 – £110
Honeywell 3 Port Mid Position Valve 22mm and 28mm £110 – £145
Drayton 2 Port Zone Valve 22mm and 28mm £55 – £100
Salus SBMV 3 Port Motorised Valve 22mm and 28mm £55 – £65

The potential costs only cover the diverter valve and not the installation, the price of which will vary depending on the installer carrying out the work. Get free quotes from multiple trusted engineers in your area by completing our online form.

What to do next

Should you find that there's an issue with your boiler's diverter valve then you shouldn't hesitate to contact a Gas Safe Registered engineer.

If your boiler was installed more than 10 years ago then you might want to consider a replacement boiler. A new boiler would run much more efficiently, run more reliably and help to reduce your energy bills.

You can get free quotes for a new boiler right here on Boiler Guide. Simply let us know you need a new boiler and we’ll take care of the rest. Then before you know, up to 3 heating engineers near you will be in touch to arrange a free quote. You can then take your time to compare them and be confident that you’re getting the very best deal.

Becky Mckay

About the author

Becky Mckay

Becky has been a writer at Boiler Guide since 2021. Her vast boiler knowledge means she’s ready to help with any home heating query, big or small!

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