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How to Free a Stuck Diverter Valve


The diverter valve is a crucial component in a combi boiler that dictates whether the hot water from the boiler is directed to the radiators or hot water outlets. And given that it is a movable component, it can easily get stuck, thereby impacting the ability of the boiler to provide heating or domestic hot water. But what exactly is a diverter valve, how does it work, and how can you free it when it gets stuck?

What is a diverter valve, and what does it do?

A diverter valve is an opening and closing mechanism inside a combi boiler that controls the flow of on-demand hot water. When you turn on your home’s central heating, the diverter valve restricts the flow of hot water to your taps and showers. On the other hand, when you turn on a hot water tap or shower, the diverter valve will cut the supply to the radiators and direct the hot water to the open outlet.

It is worth mentioning that a diverter valve always prioritises hot water demand over central heating. As such, if a hot water tap is opened when central heating is on, the diverter valve will cut off the hot water supply to the radiators and instead channel the hot water to the open hot water outlet. And once the hot tap or shower is turned off, the diverter valve will allow the hot water to flow back to the radiators.

How to tell if your diverter valve is stuck

Unlike many boiler problems requiring you to open the boiler and tinker with the mechanism, diagnosing a stuck diverter valve is an easy task. You just have to look for the following tell-tale signs that indicate that a stuck diverter valve is a culprit behind your home’s heating problems.

  • You have hot water but no central heating: The diverter valve is likely to be stuck on domestic hot water, cutting off the supply to the radiators.
  • Lukewarm water is coming out of your hot water outlets: The diverter valve will likely be stuck on the ”open” setting for central heating, meaning domestic hot water isn’t prioritised. Only some hot water is allowed through to your hot taps, which isn’t enough to make the entire flow hot.
  • You only have hot water when you turn your central heating on: The diverter valve might be stuck so that it prevents the hot water from flowing to your taps.

How to free a stuck diverter valve

As a faulty diverter valve isn’t a DIY fix, it is recommended that you leave freeing a stuck diverter valve to a certified heating engineer. This is particularly the case if your boiler is still under warranty, given that tampering with it could void the warranty. The engineer will run tests to ascertain that the diverter valve is stuck and proceed to free it or even replace the whole diverter unit if it is already worn out.

Generally speaking, the heating engineer will easily free and fix your stuck diverter valve by following these steps.

  1. Opening the diverter valve unit and checking whether it has other issues besides being stuck.
  2. Removing and cleaning the diverter valve using commercial chemical cleaners for boilers.
  3. Refit the now clean diverter valve and run tests to ensure it works correctly.
  4. Replace the entire unit if it isn’t feasible to reinstall the current diverter valve or the whole diverter unit.
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