Unvented Hot Water Systems

The Power Behind Hot Water

Unvented Hot Water Cylinders Explained

Unvented hot water cylinders were only made legal in the UK in 1986, but have since grown rapidly in popularity.

In an unvented system there is no cold water tank, instead the sealed hot water cylinder is fed directly by the cold water mains.

Since they are operating at mains pressure, they offer much better flow rates, meaning your shower and bath performance should be higher.

The other major benefit is that you don’t need to maintain a cold water tank in the loft (which vented systems require). This is good news since not only does it free up space, it also removes the potential freezing issue during our long cold winter periods.

In addition, since you aren’t relying on gravity to move the hot water around the home, the unvented cylinder can be located pretty much anywhere in your property.

Other advantages of installing an unvented system include reduced noise in the system (since there is no cold water filling of the water storage cistern), and since there is no water storage cistern and the system is essentially sealed, the cold water is not at risk from contamination.


A typical Unvented Hot Water Cylinder install can start at around £1200+vat (£1440.00) (this is not under/over sink installations)


We charge £60+vat (£72.00) p/hr for unvented hot water cylinder fault diagnosis repairs.

The most common faults with unvented hot water cylinders that need repair can


  • Hot Water pressure drops / Luke Warm Water / Boiler on but no hot water.

  • Hot water only lasts a few minutes / Water escaping through tundish /

  • Water escaping when not in use / Water not heating up when electric element is on.


Manufacturers of Unvented cylinders recommend an annual service to be carried out.

This is a requirement on many home insurance policies.

It is important for both the safety and correct operation of your Unvented Cylinder, failure to maintain and service your Unvented Cylinder could result in insurance companies failing to cover any damage if a fault was to occur.

This is also a recommendation for under & above sink unvented water heaters.

Unvented Cylinder Service £70.00+vat (£84.00)

What’s involved in an Unvented Cylinder Service?

  • Remove and clean filters/strainers.

  • Check the integrity of the cylinder for leaks or damage.

  • Check/recharge air pressure in expansion vessel.

  • Internal expansion, reset expansion gap whilst testing of the temperature/pressure relief valve.

  • Test the temperature/pressure relief valve & pressure reducing valve.

  • Visual inspect & test discharge pipes, checking termination position.

  • Checking storage and delivery temperature settings and the operation of controls or motorised valves.

  • Check the mains water pressure 

  • Check water pressure and flow rates at outlets.

  • Check and clean flow diffusers on taps if fitted.

  • Explain works carried out to customer

  • Complete the service record.


Claremont Highbridge Road Brambridge Winchester SO506HS

+44(0)7887684104 / 01962717457

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