Faulty diverter valves are a common problem, particularly with boilers that are 10 years old or above. A diverter valve determines when you can get hot water to your taps and when the water should be directed to your radiators. It’s an essential part of a combi boiler system, so what is it, how does it work and what happens when it gets stuck?
A diverter valve is a mechanism that can be found in a combi boiler system. It’s used to control the flow of water through your home’s radiators, taps and showerheads.
A combi boiler will prioritise the flow of water in your home’s system depending on what’s being used. For example, if the heating is on and you turn on a tap, the boiler will restrict the water to the radiators and will prioritise the tap. When you turn the tap off, the hot water will flow back to the radiators. This is because the combi boiler heats water on demand instead of storing it in a tank, like a conventional heating system. The diverter valve will open and close to control the flow of water.
A diverter valve works by opening and closing to allow or restrict the hot water that travels to your radiators or taps. When your combi boiler needs to send hot water to a tap instead of the radiators, the relevant diverter valve will close.
An example of a diverter valve that you may have used yourself is a shower diverter valve. If you have a showerhead over your bath, the diverter allows you to choose whether you want the water to come out of your bath taps or out of the shower head. It’s usually a lever that’s situated behind the bath taps that you can pull up or push down.
System and conventional boilers don’t require a diverter valve. This is because the hot water they produce is stored in a hot water cylinder. The heated water from the cylinder can be moved around your radiators and supply your taps at the same time. A combi boiler is different because it heats the water when there’s a demand for it.
Diverter valves can become damaged or stuck. This is because they’re a moving part and can be oscillating between being open or closed many times a day. However, they are fixable.
If you have no hot water, try turning the heating on. Wait a few minutes and try the hot water tap again. If hot water starts coming through, there may be an issue with the diverter valve.
You may have the opposite problem, whereby your hot water is coming through but your radiators are cold when your thermostat is set to a warmer temperature. This could also indicate that the diverter valve is stuck because your boiler is allowing water through to your taps but blocking off the water to the rest of your heating system.
If your hot water tap is only releasing lukewarm water, you may have a stuck valve. The valve is allowing some hot water through but not enough to make the water hot instead of warm. This is one of the most common signs that your diverter valve is faulty. It’s likely stuck on the ‘open’ setting to allow the radiators to stay warm instead of prioritising your taps.
We wouldn’t recommend fixing the diverter valve yourself. If you think there’s a problem, you should call a suitably qualified engineer to have a look at it for you.
The engineer will run a check to test whether it’s the diverter valve that’s the issue and not another underlying problem. However, in most cases, the valve may have become stuck and simply needs to be cleaned and re-fitted. The engineer might choose to replace the whole diverter unit to prevent the new valve from sticking.
You could also ask the engineer to look at other parts of your boiler while the casing is off. They could check over any other parts for wear and tear.
If your boiler is still under warranty, the valve may be replaced at no cost to you, provided you use a manufacturer-approved service technician. If the valve does have to be replaced and your boiler is out of warranty, you’ll need to pay for a new valve and cover the labour cost for fitting. A diverter valve can cost between £80 and £200. If you add around £50 for labour on top of this, you could be looking at spending from £130 to £250. If you have a boiler cover policy, this may offset the cost.
It might not be worth getting the valve replaced if your boiler is older than 10 years. Instead, you should look at a full boiler replacement to make sure you aren’t left without heating or hot water in the winter.