Just like you have your gas boiler serviced.
That just shows you what could happen if some form of failure occurred.
Unvented hot water cylinders store water supplied directly from the incoming mains water supply.
They are heated using either electrical heating elements (immersion heaters) or from a boiler.
This provides high-pressure hot water supplies capable of feeding all the hot outlets with a high flow rates of hot water.
Typically the pressure is in the region of 2 to 3 bar in the United Kingdom.
As such, they supply water to outlets at a high level, such as in a loft space, and at similar pressures to the mains cold water supply.
With both hot and cold water services fed from the mains.
There is no more need for a cold water storage tank.
This keeps loft spaces clear, and pipework to a minimum.
In order for them to work properly, they require both adequate mains pressure and flow rate.
The incoming supply pressure should typically be in the region of 2 bar.
Preferably more, and capable of supplying the required flow rates.
This wil limit the pressure of the incoming mains water to a safe level at which the cylinder is approved to operate.
The difference between pressure and flow is important to understand.
The incoming mains supply pipe sizes and flow rates, as well as pressures, should always be checked.
First is over-pressurisation, caused by a failed pressure reducing valve, or by backpressure, from a faulty mixer valve for example.
If an unvented cylinder should ever overheat and reach 100°C.
Then instead of boiling away as it would with a vented system.
At this time, the sudden reduction in pressure resulting from the split may cause water to turn rapidly to steam.
As well as the mains Pressure Reducing Valve to limit the incoming water pressure, additional protection must be taken.
This allows water to be discharged during heat up.
This is if the expansion has failed to operate correctly.
A Temperature and Pressure Relief Valve, fitted near the top of the cylinder, is required.
This allows water to be discharged when store temperatures or pressures start approaching unsafe levels.
Any water discharged in this way will typically be replaced by incoming cold mains water that will prevent store temperatures from rising further.
The Tundish allow water to be released from the store under fault conditions.
Discharge pipes are typically 15mm up to the Tundish, and then increase to 22mm to a safe discharge point outside.
Certain systems layouts and longer pipe runs will require larger pipe sizes as laid down in the G3 Building Regulations .
All indirect unvented cylinders require that the flow from the boiler to the cylinder is fitted with a Motorised Isolating Valve.
This will close when an Overheat Thermostat thats fitted to the cylinder detects an overheat.
Likewise, immersion heaters must have a built-in overheat thermostat.
Only those specific to the model and size of unit.
In addition to the use of approved safety controls.
G3 Building Regulations provide a clear indication that installers must carry certification from either the CITB, IOP, or other approved body.
A recent trend in the market for hot water systems is the growing demand for pre-fabricated systems that are factory fitted with the controls and wiring.
Pre-fabricated systems also ensure that controls have been fitted as per requirements and to a ‘standard’ pipework layout.
Such an approach can cut down installer error, reduces the risk of transit damage to safety controls, and makes for a tidier installation.
So do you need to have your unvented hot water serviced?
Like to know more about how Duval Heating can help you with your boiler and heating problems, even book an appointment for one of our engineers to call on you. Use our Contact page
01473 806 100
Duval Heating 1985 - 2019