Home Improvement

How to Free a Stuck Diverter Valve

Image source: steved_np3 / Shutterstock.com

The diverter valve is an important part of a property’s heating system. And, like any other part, it’s possible for it to get damaged through general wear and tear. If you experience an issue with the diverter valve of your combi boiler, your heating system wouldn’t work as efficiently as it normally should.

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An issue with the diverter valve would require opening up the boiler and tinkering with the mechanism. The Fantastic Services team recommends leaving these tasks in the hands of capable technicians. So, this article is for all of you who wish to get an overall education on how to free a stuck diverter valve.

What is a diverter valve?

A diverter valve is a mechanism inside your boiler used to control the flow of water through your entire heating system. This includes your taps and showerheads, and radiators. Through the diverter valve, a combi boiler will control the flow of hot water depending on which fixture is being used.

How does a diverter valve work?

System and conventional boilers don’t require a diverter valve, since they store the hot water in a cylinder. You can only find it on a combi boiler because they heat the water on demand. A boiler’s diverter valve has the same function as the one on a showerhead – it controls the flow of hot water to different destinations. 

When it comes to a home heating system, the diverter valve would open in order to let the heat reach the radiators. Once there is a demand for hot water in the tap or showerhead (usually when you switch on the hot water), the valve would close. If you’re not using the taps or showerheads, the diverter valve would stay open to keep the radiators warm.

Symptoms of a faulty diverter valve

There are three most commonly occurring plumbing issues if you happen to have a faulty diverter valve. They are as follows:

  • Taps not getting hot water. The most common symptom of a faulty diverter valve is when you don’t get any hot water to your taps and showerheads. The water gets luke-warm at best, but no more. This means that the boiler isn’t prioritising the hot water to the fixture in use, because the diverter valve is stuck open and the heat is escaping.
  • Lots of hot water, but no heating. When you switch on the heating system during the colder months, your radiators should be warm and hot water should be reaching the taps. However, if you have hot water in the taps and showerheads, but no room heating, then you have the opposite of the previous issue – the diverter valve is stuck closed and isn’t letting the heat reach the radiators. If your heaters are only cold at the bottom, though, there’s a different issue.
  • You have hot water only if the heating is on. If you’re not using your heating system in summer, you should still be able to have hot water reaching the taps and showerhead. If you don’t have hot water when the heating is off, but you do when the heating is on, then once again you have a faulty diverter valve.
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How to test a boiler diverter valve

Let’s assume that you are experiencing the most common symptom of a faulty diverter valve – not getting hot water. In order to test and know for sure that’s where the problem is, here’s what you should do:

  1. Open the boiler and locate the diverter valve. If this already seems like a challenging task, it’s better not to do it yourself. After you remove the lid of the boiler, you have to locate the diverter valve mechanism.
  2. Run tap water on hot and observe the diverter valve. If you run hot water, the valve is supposed to close in order to divert it to the tap, meaning it should move. If you see no movement, then it’s stuck.

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How to free a stuck diverter valve

We don’t recommend fixing the diverter valve yourself. If you think there’s a problem, you should call a qualified engineer to have a look at it.

  1. Check for other problems.

    Before doing anything to the diverter valve unit, it’s important to look over the entire mechanism of the boiler. Even if you’re 100% certain the valve is faulty, there could be another issue as well. Tinkering with parts of your boiler could result in additional damage.

  2. Clean the valve.

    If the valve is the only issue, it probably got stuck due to corrosion. There are commercial chemical cleaners for boilers on the market. However, it’s important to know which one to use and when to use it. If you’re not careful you might cause additional damage to your boiler mechanism.

  3. Replace the valve.

    A reliable boiler technician will perform the right checks and in the end will determine whether they should clean the stuck diverter valve, or replace it with a new one altogether. Replacement of the whole diverter unit is a delicate procedure and should be performed only by a certified engineer.

If your boiler is still in warranty and you need to have the diverter unit replaced, the process will be done with no cost to you. If your boiler is out of warranty, you would have to pay for the replacement of the valve and for the technician’s labour. If they find more faults in the boiler mechanism and especially if it was installed more than 10 years ago, you might be advised to buy a new one altogether.

Hire a professional

The professional technicians from Fantastic Services DO NOT recommend for any homeowner to do boiler repairs on their own (if they’re not certified technicians themselves). If you attempt to do anything to the mechanism, you could lose your warranty. If your boiler is out of warranty, you would have to pay for the repair and replacement of parts from your pocket. The reliable technicians from Fantastic Services are always ready to help with any boiler issues you may have.

And, if you join our Fantastic Club, you’ll get reduced rates and preferential booking slots for more than 25 services, including boiler repair. Find out what Fantastic Club is.

Visit the main website for price rates on our professional boiler repair technicians!


  • The diverter valve helps keep your home heating system in working order;
  • If a diverter valve is stuck open, it won’t let hot water reach your taps and showerheads;
  • If a diverter valve is stuck closed, it won’t let your radiators warm up the room;
  • The most common repair method is either cleaning or replacing the diverter valve;
  • Always call a certified technician if you have a problem with your combi boiler, especially if it’s still in warranty.

If you find that you have hot water but no heating (or the opposite), a faulty diverter valve is the likely culprit. But that’s not always the case. If you have found yourself with no heating or hot water, take a look at our blog post on the topic next to find out what you can do.


Have you ever had to deal with a stuck diverter valve at home? How did you handle this issue? Share your experience in the comments!

Image source: James C Davis/shutterstock.com

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