
8
SIENA
Digital electronic water heater
4.6. Expansion relief valve
This must be installed between the pressure reducing valve and the water heating unit in accordance
with Figure 2 (page 7). No other valve should be fitted between this valve and the cylinder. The
expansion relief valve contains a non return valve.
4.7. Expansion vessel
A suitable expansion vessel (Figure 2, page 7) with a pre-charge pressure of 0.15 or 0.3 MPa is
available in an optional kit for fitting to all water heating units in the range. The expansion vessel
MUST be fitted to the safety group. The expansion vessel MUST be positioned with the entry point at
the bottom – see Figure 2 above.
IMPORTANT: Regular checks must be carried out to ensure that the expansion vessel is correctly
pressurised to 0.15 or 0.3 MPa at all times. – see Figure 2 (page 7).
4.8. Tundish
The tundish (Figure 2, page 7) must not be positioned above or in close proximity to any electrical
current carrying devices or wiring. The installation should conform with the requirements of section
4.9 below.
4.9. Discharge arrangement
The tundish (Figure 2, page 7) must be installed in a position so that it is clearly visible by the user. In
addition, the discharge pipe (Figure 2, page 7) from the tundish should terminate in a safe place where
there is no risk to persons in the vicinity of the discharge, be of metal and:
A) Be at least one pipe size larger than the normal outlet size of the safety device unless its total
equipment hydraulic resistance exceeds that of a straight pipe 9m long, i.e. discharge pipes between
9m and 18m equivalent resistance length should be at least two sizes larger then the normal outlet
size of the safety device, between 18m and 27m at least three sizes larger and so on. Bends must be
taken into account in calculating the flow resistance. Refer to Figure 3 (page 9), Table 1 (page 10) and
Calculated Example 1 (page 10).
B) Have a vertical section of pipe at least 300 mm long below the tundish before any elbows or bends
in the pipework.
C) Be installed with a continuous fall.
D) Have discharges visible at both tundish and the final point of discharge, but where this is not
possible or practically difficult, examples of acceptable discharge arrangements are:
• Ideally below a fixed grating and above the water seal in a trapped gully.
• External surfaces such as car parks, hard standings, grassed areas, etc.) are acceptable
providing that where children play or otherwise come into contact with discharges, a wire cage