How to free a stuck diverter valve

Is your combi boiler running your heating 24/7 but not firing up any hot water? Chances are your diverter valve is sticking. Find out how to free a stuck diverter valve.

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This guide runs through how to free a stuck diverter valve with the help of a Gas Safe registered heating engineer.

But first up, what is a diverter valve, and how do you know if it's stuck?

What is a diverter valve?

Diverter valves are crucial in directing hot water from combi boiler heating systems to our home’s radiators, taps, showers and underfloor heating. They work automatically, busily opening and closing throughout the day to divert hot water where needed.

However, problems arise when your central heating diverter valve becomes stuck—a common issue with older boilers. While this can wreak havoc on your heating and hot water supply, it can be easily fixed with the help of a Gas Safe registered heating engineer.

Signs a diverter valve is stuck

If your diverter valve is sticking, you’ll soon know about it. Whether that’s standing under a cold shower because you’ve got no hot water or facing a chilly evening because your radiators won’t switch on.

Other things to look out for include:

No hot water from the taps
Lukewarm water – a common issue when a diverter valve is stuck in mid-position
Radiators not heating fully
Boiler overheating
Whirring or banging noises from the boiler or pipework
Hot water and heating on at the same time (when they shouldn’t be!)
Boiler not responding to thermostat
Hot water supply coming and going unpredictably
Low water pressure

How to free a stuck diverter valve?

A stuck diverter valve on a combi boiler isn’t a DIY fix. That’s because you’re dealing with electrics and gas components.

Only a Gas Safe registered heating engineer can repair a stuck or faulty diverter valve. How they do that depends on the model and make of your combi boiler.

Common combi boiler manufacturers include Honeywell, Glow Worm, Baxi Duo Tec, and Worchester Bosch, and the size and type of the diverter valves are different for each. The exact location of the diverter will vary, too, depending on the make and model.

In the best-case scenario, your boiler diverter valve is sticking simply because of wear and tear. A heating engineer will clean the valve using a commercial chemical cleaner and then refit it.

However, if the diverter valve is beyond repair, you’ll need the diverter valve to be replaced.

How much do diverter valve repairs cost?

Because each combi boiler manufacturer uses different types of diverter valves, it’s tricky to give an exact cost for a replacement.

However, to give you a general steer, a gas central heating engineer typically charges an average hourly rate of £65 + repairs & parts.

Top tip – If your combi boiler is still under warranty, you might be able to have a diverter valve replaced for free. Just make sure that the replacement is fitted by a Gas Safe heating engineer approved by the manufacturer.

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How to find a Gas Safe registered heating engineer

Unless you’re a qualified engineer yourself, trying to repair the diverter valve in your combi boiler yourself is never a good idea.

You’re dealing with a vast network of wiring and gas components, and you could do more harm than good.

You’ll need a Gas Safe registered heating engineer to fix the problem. They can also help with an annual service of your combi boiler to stop your diverter valves from sticking in the future and keep your boiler in working order for longer.

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FAQs

How do you unblock a diverter valve?

If it’s repairable, a Gas Safe registered heating engineer will remove the valve, clean it using a commercial chemical cleaner, and refit it.

How do you unstick a stuck water valve?

A professional will use pliers to slowly move the stuck valve back and forth to loosen it. Due to the presence of gas and awkward valve positioning, this isn’t a job you want to do yourself.

Can you manually open a diverter valve?

While it is possible to open some diverter valves manually, we don’t recommend it, as you could damage the valve.

What happens when a diverter valve fails?

If your combi boiler’s diverter valve fails, you’ll either have no hot water or heating. But if you’re really unlucky and the valve is completely broken or blocked, you might be faced with a combination of both.

Is a faulty diverter valve dangerous for a combi boiler?

While a faulty diverter valve isn’t considered dangerous, it could damage other components in your boiler and cause a leak or overheating. If left unrepaired for too long, it could also cause irreparable damage, and you might need to replace your entire boiler – not ideal!

The good news is that a professional can easily and relatively inexpensively repair stuck or faulty diverter valves.

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