Forget the kettle, top tips for installing instant hot water taps

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Date posted: 21st Oct 2022

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Reading time: 4 minute read

Close Up Of Man Making Hot Drink From Boiling Water Tap

Instant hot water taps are an on trend plumbing feature in today’s plumbing and heating landscape - who doesn’t want to instantly make a cup of tea or coffee after all? However, instant hot water taps require a surprisingly large amount of infrastructure in order to operate effectively.

So, what are instant hot water taps?

Instant hot water taps are essentially a result of cold water being fed through an unvented hot water cylinder, but a much smaller one that is kept underneath a kitchen sink. If that sounds like it could potentially cause scalding, then you’d be right. However, the cold-water supply that feeds into the cylinder is heated up in a much different manner to traditional hot water taps. In fact, it is not the water itself that is being pushed out of the tap, but steam that then forms into condensation and fills your mug or glass with hot water. This means that there is a lower risk of scalding than traditional hot water taps. Having said that, it is still recommended that the right safety features be put in place, which is why we are on hand with our top tips for plumbing in instant hot water taps.

boiling water tap in kitchen

Baseline safety precautions

Speaking of safety features, our first top tip for installing instant hot water taps relates to the key valves that should be put in place for the hot water cylinder to work effectively. These are different from the typical valves you would find on a tap. Simply put, because the water is heated differently, the recommended safety valves are different, too. One major difference is the option of fitting a tempering valve such as the Heatguard Tempering Valve from RWC’s Reliance Valves. This valve limits the water temperature to 70°C, which is a much safer temperature.

Therefore, you need to have a pressure relief valve, such as the 102 series potable water pressure relief valve from the Reliance Valves range. These act as a secondary form of hot water protection. The cylinder itself has a cut off feature that prevents temperatures from exceeding 110°C, however, pressure relief is required as a failsafe. The valves are designed to be installed directly to the upper portions of a hot water cylinder, as this is where the hottest temperature is found. If the valve is opened, it will lift off its seat and release the water to a waste deposit, which reduces the pressure within the cylinder.

Keep an eye on the cold-water supply

One thing that often receives less consideration is the cold-water supply that feeds into the cylinder. Depending on where in the country you are installing an instant hot water tap the pressure of this cold supply can be extremely high.

In domestic properties especially, it is extremely important to have the right pressure reducing valves in place to ensure that there is a constant, regular pressure going to the cylinder. Valves such as the Predator Pressure Reducing Valve from Reliance Valves can effectively reduce the pressure running through a system to 1.0 bar from as high as 6.0 bar, which gives you control of not only the pressure but the flow rate through the valve. Additionally, if you do have times when the pressure is fluctuating up and down, as is often the case in commercial buildings, the hot water cylinder itself is protected.

Predator Pressure Reducing Valve

Fit an expansion vessel

As stated in Part G of the Building Regulations, fitting an expansion vessel on hot water cylinders is a legal requirement, and we thought it would be useful to explain why this is the case.

During the warmer months, the ambient room temperature can begin to heat up the cold-water pipes, which often have no lagging on them at all. This means that water that is supposed to be between 5°C and 10°C can be heated to between 20°C and 30°C, which is problematic, as it’s not working as intended, and poses a massive legionella risk too. So, it is important to make sure that the pipes are adequately lagged in the first place, however, this temperature increase can still occur.

Due to the heat, the cold-water supply that is feeding into the hot water cylinder, is expanding, and sometimes doesn’t have physically enough room inside the pipe to go anywhere. This is why the expansion vessel is required as a safeguarding tool to prevent the cold-water supply pipes from bursting. The vessel does need to be sized correctly, and manufacturers like RWC have technical support available to help you find the right expansion vessel, but at the very least it needs to have a two-litre capacity. You will sometimes see an expansion vessel attached to the hot water cylinder too, but that is less common as most of these safety features are already built into the cylinder itself.

By keeping these things in mind, you should have no issues plumbing in instant hot water taps in domestic or commercial buildings while keeping your customers both safe and happy with their instant cups of tea.