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Last updated: 16th April, 2024


How to Fix a Faulty Diverter Valve

How to Fix a Faulty Diverter Valve

One of the most common reasons for heating and hot water to stop working properly is a faulty diverter valve. In this guide, we’re going to be taking a look at what a diverter valve is, how to spot if it is faulty and how you can fix it.

What is a Diverter Valve?

A diverter valve is a component inside a combi boiler which controls the flow of water through the radiators, taps and showers in your home.

As a combi boiler works to provide instant hot water on demand, it doesn’t have a hot water storage tank, so it must prioritise whichever appliance is being used.

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For example, when the heating is on and you turn on a hot tap, the boiler must restrict the hot water to the radiators and prioritise the tap.

When the tap is turned off the hot water then flows back to the radiators. This process works via the diverter valve.

The diverter valve opens and closes to allow or prevent the hot water from travelling to your taps or radiators, so when the combi boiler needs to send hot water to your taps, it will close the relevant radiator valve and vice versa.

Is My Diverter Valve Faulty?

Sometimes, the diverter valve can get stuck or become damaged as they are frequently switching between the open and closed settings throughout the day, making it more susceptible to faults.

This can mean you either get no hot water because the valve is stuck open on the heating or it could give you the opposite problem, where you have hot water but cold radiators.

Signs Your Diverter Valve is Faulty

A fault diverter valve is most common in older boilers over 10 years old, however, they can become stuck on any boiler so it’s good to know some of the signs so you can spot it and get it fixed sooner.

Some common signs of a faulty diverter valve are:

You have hot water, but cold radiators

If you find yourself with hot water but no heating even when the thermostat is set to a higher temperature, this is usually a clear indicator that your diverter valve has become stuck.

You have no hot water unless you turn the heating on

If you find yourself with no hot water when you first turn on your tap, turn on the heating and wait a few minutes before trying your hot tap again. If hot water starts to come out, this suggests that it is likely your diverter valve is faulty.

Your hot tap water is lukewarm

If your hot water tap is only producing lukewarm water, your diverter valve may be stuck on the ‘open’ setting for your radiators, making your taps a lesser priority.

This is because the valve will likely be allowing only some hot water through but not enough to make the entire flow hot. This is one of the most common signs of a faulty diverter valve.

How to Fix a Faulty Diverter Valve

Unfortunately, due to the position of the diverter valve within the combi boiler and the regulations on Gas Safety, a faulty valve isn’t a DIY fix. We would recommend calling out a Gas Safe engineer to take a look at it for you to ensure everything is left running safely and smoothly.

The engineer will do a few tests to check whether the diverter valve is responsible for your heating and hot water issues and not another faulty component.

However, generally, it will be down to the valve that has become stuck and the engineer will either clean and refit it or replace the whole diverter unit to prevent it from sticking in future.

If your boiler is still under its warranty, you may be able to get a diverter valve replacement at no extra cost if fitted by an engineer that is approved by the manufacturer.

Otherwise, you may have to pay between £80 to £200 on a new diverter valve with the additional cost of labour (usually around £50).

One way to ensure your boiler remains under warranty is by getting it serviced annually by a Gas Safe engineer.

Not only does this maintain your warranty, it also helps to keep your boiler running smoothly, safely and efficiently and can even prevent issues such as a stuck diverter valve in the future as the engineer can spot the early signs before it becomes a much bigger problem.

How A New Boiler Can help

If your boiler is over 10 years old and is no longer under warranty, it may be worth replacing it as you may notice more and more issues arising that can become incredibly expensive to fix over time, not to mention, new boiler models are significantly more efficient, helping you to save up to £380 each year on your boiler bills. 

Age of Boiler

Efficiency Percentage

Efficiency Rating (ErP)

0+ Years

90% +


10+ Years

85% +


15+ Years

80% +


20+ Years

70% +


25+ Years

60% +


The direct correlation between a boiler's age and its efficiency is clear to see in the newer systems’ ErP. 

Why not take a look at our brand new A-rated efficient boilers and get a free quote today?

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Frequently Asked Questions

Can I Fix a Diverter Valve Myself?

Yes, you can attempt to fix a diverter valve yourself if you have some basic plumbing skills and are comfortable working with your boiler system. The task usually involves either cleaning the valve to remove any debris or replacing it if it's faulty. However, considering the critical role the diverter valve plays in directing the flow of hot water in your heating system, it's important to be cautious. If you are unsure about the process or if the repair involves complex disassembly, it’s safer and more effective to call a qualified heating engineer.

What Happens When a Diverter Valve Goes Bad?

When a diverter valve malfunctions, it can lead to significant issues within your heating system:

  • No hot water or heating: The valve may fail to switch between hot water and heating modes, leaving you without one or the other.
  • Leaking: A faulty valve can sometimes cause leaks within the system, leading to water damage or loss of pressure.
  • Boiler shuts down: Some boilers may shut down as a safety precaution if the diverter valve is not functioning correctly.

These symptoms not only affect your comfort but can also lead to greater energy use and increase wear on other parts of the boiler.

How Much Does it Cost to Replace a Diverter Valve?

The cost to replace a diverter valve can vary based on the model of your boiler and the rates charged by the technician. Typically, you can expect to pay between $250 to $600 for a complete replacement, including parts and labor. This price can be on the higher end in areas with higher costs of living or for boilers that are less common and require more expensive parts.

Can You Reset a Diverter Valve?

While you cannot "reset" a diverter valve in the traditional sense, as they are mechanical parts, you can sometimes restart your boiler to clear any electronic faults that might be affecting the valve's operation. If the valve itself is stuck or clogged, this won't resolve the problem, and mechanical intervention will be necessary.

How Do I Know if My Diverter Valve is Broken?

Indications that your diverter valve may be broken include:

  • Inconsistent water temperature: Fluctuations in water temperature or failure to provide hot water when the central heating is off.
  • Strange noises: Knocking or banging noises from the boiler when it tries to activate the hot water.
  • Heating comes on with hot water: The central heating radiators warm up when you turn on the hot water, even if the heating is set to off.

Can You Manually Open a Diverter Valve?

It is possible to manually manipulate some diverter valves to force them into the open or closed position, which can be useful for diagnosing problems or providing a temporary fix. However, this should be done cautiously to avoid damaging the valve. Not all valves are easily accessible or designed to be manually adjusted, so refer to your boiler's manual or consult a professional.

How Do You Unclog a Diverter?

To unclog a diverter valve:

  1. Isolate the Boiler: Turn off the power to ensure safety.
  2. Access the Valve: Depending on your boiler model, this might involve removing the boiler casing or access panels.
  3. Inspect and Clean: Look for any visible debris or corrosion that could be causing the valve to stick. Clean the valve carefully, and check the surrounding pipes and connections for blockages as well.
  4. Reassemble and Test: Once cleaned, reassemble your boiler and restart it. Check if the issue with the diverter valve persists.

Unclogging a diverter valve can sometimes resolve issues, but if the valve is worn or damaged, it may need to be replaced. If you're unsure about any step or if cleaning doesn't solve the problem, it's wise to contact a professional to avoid damaging your boiler or causing further issues.

Stephen Day profile photo
Article by
Stephen Day | Co-founder
Gas Safe registered and FGAS certified engineer with over 20 years experience in the heating and cooling industry.