How to Fix a Faulty Diverter Valve

Last updated: May 11, 2024

A faulty diverter valve is common among combi boilers, especially if you have an older boiler. Read on to discover how to fix a faulty diverter valve and return your heating and hot water.

A diverter valve is a vital part of a combi boiler heating system since it determines where hot water is sent throughout your home.

Combi boilers don’t have hot water storage tanks and work by providing instant hot water on demand. Therefore, they must prioritise where to send hot water, and that’s where diverter valves come in.

Diverter valves direct the flow of hot water to taps, radiators, or showers. For example, if the heating is on and you turn on a hot tap, the boiler must prioritise the tap and restrict the hot water to the radiators.

The process works through the diverter valve, which opens and closes to direct hot water. A faulty diverter valve can fail to perform this crucial function, resulting in chaos in your home’s heating system.

This guide explores what a diverter valve is, the warning signs that a diverter valve could be developing a fault, how to fix a faulty diverter valve, and the average costs you can expect for repairing a diverter valve.

How to fix a faulty diverter valve in a combi boiler

Key Takeaways:

  • Symptoms of a faulty diverter valve include lukewarm water, only getting hot water when you leave your heating on, and having hot water but no central heating.
  • Only a qualified Gas Safe Engineer should fix a faulty diverter valve.
  • You can expect to pay anywhere between £250 to £350 to replace a diverter valve.
  • Getting a new boiler instead of repairing or replacing the valve of an old boiler is more cost-effective in the long term.

What is a Boiler’s Diverter Valve?

A diverter valve is an internal boiler component that opens and closes to direct the hot water flow from the boiler.

Diverter valves can direct water to the radiators or the shower and taps and are unique to combi boilers.

They allow you to control where hot water is sent on demand. They’re usually not found on conventional or system boilers, which store hot water on storage cylinders.

The diverter valve directs the hot water to the tap instead of the radiators when you turn the hot water tap on. When you turn the heating on, the diverter will do the same for the radiators.

However, it will prioritise sending hot water to the shower or tap when the heating is on, and you turn on the hot tap or shower. The hot water will only go to the radiators when you turn off the tap or shower.

Wondering which boiler manufacturers performed best? Check out our best boiler brands guide for the full rundown and if you are trying to determine who the best boiler installation company is, check out our Warmzilla and Boxt reviews.

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How Do You Know You Have A Faulty Diverter Valve?

Diverter valves perform a mechanical function and open and close continuously. After several years, they can get worn out, start sticking, or generally misbehave.

You may experience one or more of the following issues indicating a potentially faulty diverter valve. These include:

Luke-warm Hot Water in Taps and Showers

Luke-warm water from taps and showers, despite the boiler system running, is the most common symptom of a faulty diverter valve.

Diverter valves are designed to prioritise hot water outlets when in use instead of heating.

However, when there is a fault or a blockage, the diverter valve may be stuck in directing the hot water to the radiators, making your outlets a lesser priority.

As such, the water flow rate may not be enough to provide the necessary heating output, and the temperature is never satisfactory.

You Only Get Hot Water When You Leave The Heating On

Homeowners usually notice faulty diverters in warmer months, like summer, when you don’t need central heating.

You may find that you only get hot water when you turn on central heating.

This is a common sign that your boiler’s diverter valve has developed a fault, and may be sticking and preventing water from flowing to the taps.

Did you know the efficiency of your boiler can impact the amount of energy it uses and ultimately impact your heating bill costs? Check out our guide to the best condensing boilers to learn more. 

You may also find our review of the best eco-friendly boilers of interest.

You Have Hot water But No Central Heating

Another frequent symptom of a faulty diverter valve is when the valve may become stuck only on the hot water side, resulting in no heating.

The taps and showers may have running hot water, but the radiators remain cold, even when you set a higher temperature on the thermostat.

In such cases, the diverter valve cannot open to allow hot water to flow to the radiators.

How To Fix A Faulty Diverter Valve

Experiencing any of the above issues can be frustrating, so it’s worth knowing how to fix a faulty diverter valve.

Fixing a faulty diverter valve isn’t something you should try to DIY.

Heating Expert Patrick Garner recommends calling a qualified Gas Safe Engineer for suspected internal issues like a faulty diverter valve.

Regulations require anyone carrying out gas work or working on gas fittings or storage vessels like boilers to be registered with the Gas Safe Register.

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The engineer can safely open up the boiler unit to diagnose your boiler problem and determine whether a faulty diverter valve or something else is causing your issues.

If the engineer spots a faulty diverter valve, they can fix it by removing it and cleaning it with chemical cleaning agents, before refitting it. In most cases, this is usually enough to get the valve moving as it should.

However, if the fault is more severe, the engineer may need to replace the diverter valve completely to get the heating and hot water working properly.

What are the Average Costs of Replacing a Diverter Valve?

You can expect to pay anywhere between £250 to £350 to replace a diverter valve.

The costs can vary depending on factors like:

Labour Costs

Labour rates usually vary depending on where you’re located in the UK. Places like London are significantly more expensive than other areas.

You also need to consider the ease and urgency of the installation. A challenging boiler will take longer and cost you more since engineers charge on a per-hour basis.

If you’re making an emergency call, you can expect to pay a premium.

Diverter Valve Cost

The cost of boiler parts like diverter valves is constantly changing, and prices can vary tremendously depending on the model of your boiler.

You can expect to pay around £200 for a diverter valve, but some manufacturers charge more without including labour costs.

If the boiler is fairly new, the parts may be covered under the original manufacturer’s warranty obtained when purchasing the boiler. In such cases, you can replace the diverter valve free of charge.

Is It Better To Get A New Boiler?

In some cases, it may be more economical in the long term to replace the entire boiler system, especially if your combi boiler is close to the end of its life or is over 10 years old.

You’re likely to experience more and more faults and issues with an old boiler. They’ll be more expensive to fix over time, especially if other parts also suffer from wear and tear.

Additionally, modern boilers are more efficient than older boilers. According to the Energy Savings Trust, replacing an old boiler with a new A-rated boiler can save you from £120 to £640 annually, depending on your home type, and where you live in the UK.

The table below shows how efficiency drops as your boiler ages:

Boiler AgeEfficiency PercentageEfficiency Rating (ErP)
0+ Years90% +A
10+ Years85% +B/C
15+ Years80% +C/D
20+ Years70% +E/F
25+ Years60% +G

Purchasing a new boiler may be more cost-effective than repairing or replacing a faulty valve on an old boiler.

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You’ll also benefit from increased efficiency and save on fuel costs. A new boiler will also come with modern technology and a new product warranty, which provides peace of mind from future breakdowns.

Do you have a common boiler problem? Check out our quick-fix guide on boiler lockout, boiler ignition faults, boiler PCB faults, faulty diverter valves, and boiler timer issues.

Summary of How To Fix A Faulty Diverter Valve

The diverter valve is a vital combi boiler component that works by opening and closing to direct hot water to your radiator for central heating or to your taps and showers.

You can experience various issues if you have a faulty diverter valve. These include lukewarm water, only getting hot water when you leave your heating on, and having hot water but no central heating.

You must call a qualified Gas Safe Engineer to fix a faulty diverter valve. They can repair it by cleaning and refitting it or replacing it completely to get the heating and hot water working properly.

Depending on the age of your boiler, it may be more economical to get a new A-rated condensing boiler to save on fuel bills.

What size boiler is right for your home? If you are considering a combi boiler, it is largely determined by the number of radiators in your home.

Check out our complete guide to new boiler installation here if you are wondering about the best type of boiler for your home. 

How much may a new boiler cost? Are you considering converting from a conventional to a combi boiler? Use our boiler installation cost calculator to get an estimation.

If you require any assistance with a faulty boiler or are researching purchasing a new one, contact our friendly team. They can assist with answering your questions and provide a free, no-obligation quote.

Frequently Asked Questions

Can I Fix A Diverter Valve Myself?

No. Safety regulations emphasize that anyone working on a boiler must be a Gas Safe engineer. Carrying out any work on the appliance when you’re unqualified can be dangerous and can result in further damage to the boiler.

If you suspect an issue with your diverter valve, ensure you call a qualified Gas Safe registered engineer to diagnose the problem.

What Causes A Diverter Valve To Leak?

Dirty contaminated water in your heating system can cause the diverter valve to leak over time through the O-ring seal of the valve. The fault is common among older boilers that are over 10 years old.

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