To install new unvented hot water heater  -not Including the electrical supply, Installation of any safety devices required 

New or replacement 

15L< less don’t always require additional safety devices when in compliance with certain on site conditions I.e.  

minimum requirements  

2.8meters ( 10 l) or 4.2 meters 15 l) of pipework before nearest cold draw off is required for expansion in pipework. Otherwise expansion vessel needed ( sometimes this is recommended ) 

Figure 4 – For inlet pressure up to 0.41 MPa (4.1 bar) recommended pressure reducing valve on high mains water pressure