Boiler Diverter Valve Problems and How to Fix Them

In most UK households, modern Combi boilers are installed as part of the central heating system. Being highly energy-efficient, it is considered the best option today for heating rooms and supplying hot water to taps and showers.

At times, you may face an annoying situation with these combi boilers, such as no hot water in taps and showers, and inconsistent or even no heating in rooms. Among many other possible reasons, a faulty diverter valve is often the actual cause of this unwanted event, especially during extreme cold conditions. The detection and repair of any fault in a diverter valve requires a thorough inspection by a Gas Safe Registered engineer, as it may involve working on gas as well as the internal components of the boiler. However, homeowners need to be aware of the basics of common signs indicating a possible diverter valve failure.

This blog will guide you through the complete process of safely checking whether the problem is with the diverter valve before you call a Gas Safe Registered engineer.

Understanding the Working of a Diverter Valve

The main feature of a Combi boiler is its ability to produce hot water only when required, either for heating via radiators or for direct supply to taps and showers. A diverter valve is the device that controls the flow of hot water where required. This feature makes a Combi boiler more energy efficient by preventing wastage of hot water.

When set correctly, the diverter valve automatically controls the flow of hot water from the boiler. In simple terms, when you turn on a tap or shower, the diverter valve automatically diverts the flow of hot water to it. Likewise, when the heating is turned on, the hot water starts flowing towards the radiators.

Accordingly, there might be three different scenarios in a household, where the diverter valve plays its role as follows:

1. Only For Heating purposes – When only heating is turned on, it would send all the hot water to the radiators, whereas taps and showers will not receive hot water until they are opened.
2. Only For Use in Taps and Showers – When any tap or shower is turned on, all hot water flow is diverted to them, whereas hot water flow to radiators is completely discontinued. 
3. For Both Purposes Simultaneously – When heating is on and taps and showers are turned on, the diverter valve sends hot water to taps and showers as a priority, with radiators as the second priority.

Advantages of a Diverter Valve

• It facilitates the flow of hot water when and where required. 
• It ensures a hot-water supply to taps and showers as a priority, without compromising the central heating system.
• Being energy efficient saves energy by minimizing waste, efficiently managing the flow of hot water.

How To Know If My Diverter Valve Is Faulty – Common Signs

The purpose of a boiler is to produce hot water for use in a central heating system and for supply in washrooms and kitchens. While any disruption in this prime function of a boiler might result from multiple malfunctions within the boiler itself or its other components, a significant reason might be a faulty diverter valve if it is a combi boiler.

Here are some of the most common, yet apparent, signs indicating that the diverter valve has developed a fault or may have failed:

• The first and most prominent sign of a failed diverter valve is that there is no hot water at taps and showers when the heating is off. When heating is turned on, taps and showers also get hot water. It happens when the diverter valve gets stuck in the "heat only" position.
• The boiler is producing hot water, but there is no heating; the radiators are completely cold. It means the diverter valve is not sending hot water to the radiators. 
• Lukewarm or cold water in taps and showers is an indication that the diverter valve is stuck in a mid-position, which results in less hot water flow towards hot taps. This may also cause hot water flow to radiators, even when heating is not on. 
• Sometimes, reduced water pressure in taps and showers can occur when the diverter valve is not working correctly.
• An inconsistency in heating is caused by a faulty diverter valve, which results in fluctuating hot-water temperature in the radiators. This situation may also occur in hot taps, where you may experience intermittent hot and cold water.
• Sometimes, the boiler may start making unusual sounds, such as gurgling, banging, or knocking, especially when switching between heating and hot water supply. This is also a clear sign of a faulty diverter valve.

Although the presence of one or more of these signs and symptoms is apparently not dangerous, it points to a significant fault in the boiler's internal components, most likely the diverter valve.

How and Why a Diverter Valve Gets Faulty - Common Reasons 

There might be multiple reasons behind a faulty or failed diverter valve. Some of them are summarized here:

• Wear and Tear – A diverter valve is a mechanical device. Like any other mechanical part of a boiler, it tends to wear out with consistent usage. Even if everything goes fine, a diverter valve may still develop a fault over the years.
• Jamming Problems – Sometimes a blockage or jamming may occur in a diverter valve due to sludge accumulation, which often circulates in the heating system and is caused by corrosion particles. It is a widespread occurrence, which is why it is usually recommended to power-flush the entire system to remove accumulated debris.
• Failed Actuator – It often happens that, despite the valve body being perfectly functional, the actuator/motor or head fails for some reason, rendering the diverter valve ineffective.
• Electrical Parts Failure – Sometimes the electrical control mechanism fails, resulting in the diverter valve failing. It may include faults in wiring or PCB, or even thermostat issues. 
• Manufacturing Fault – Though rare, a diverter valve may stop working over time. In some cases, it may keep working normally, but over time, it may become blocked by accumulated scale. 

How to Fix a Faulty or Failed Diverter Valve?

Since a diverter valve is an internal component of a boiler, it is not recommended to fix it yourself. As per the Gas Safety (Installation and Use) Regulations 1998, only a Gas Safe Registered engineer is authorized to work, repair, service, and replace a boiler or its internal parts. So, never try to fix the faulty diverter valve yourself.

However, if one or more signs of a faulty diverter valve appear, you can perform the following basic checks before calling a gas-safe registered engineer:

• Try to resolve the issue by restarting the boiler. Please turn it off and wait for at least one minute. Turn it on again and monitor its performance for a while. If the problem is minor, it may vanish when the boiler is restarted.
• Check the thermostat settings and other control devices, such as the programmer and room temperature settings. If hot water does not flow normally only when a timer is activated, the real problem might be with the controls rather than the diverter valve. 
• You can also check the actuator's operation by hearing a specific sound. Turn on the hot water, then turn on the heating. At this stage, you can notice a distinct sound from the valve's movement. If there is no such sound, it indicates that the actuator is faulty. On the other hand, if a clicking sound occurs but the problem persists, it might suggest that the valve is stuck.

Important

If, after performing the above checks, it transpires that the fault lies with the diverter valve, or if you are unsure about the outcome of your checks, it is time to call a Gas Safe-registered engineer.

Conclusion

A diverter valve is a mechanical component of a boiler. Hence, it is just an everyday happening if it develops a fault or completely fails. While it is not an immediate danger, it might be a serious cause of annoyance. Ignoring it for a long time may also result in severe damage to the boiler, leading to higher costs. So, timely detection of the fault is important. If the symptoms point to a faulty diverter valve, call a gas-safe-registered engineer; don't try to fix it yourself, as it is a violation of gas safety regulations. Get it repaired or replaced, as advised by the engineer, to ensure consistent heating and hot water in showers and taps.