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union. The pipe work from the relief valve to the drain should be as short as possible and fall all the way
from the water heater with no restrictions. It should have no more than three right angle bends in it. The
drain line must be the same size, or larger, than the relief valve outlet to which it is connected.
The outlet of the drain line must be in such a position that flow out of the pipe can be easily seen (refer
to AS/NZS 3500.4) - but arranged so hot water discharge will not cause injury, damage or nuisance.
The drain line must discharge at an outlet or air break not more than 9 metres from the relief valve.
In locations where water pipes are prone to freezing, the drain line must be insulated and not exceed
300 mm in length. In this instance, the drain line is to discharge into a tundish through an air gap of
between 75 mm and 150 mm.
The drain lines from each relief valve can discharge into a common tundish. This also applies to the
drain lines from each water heater in multiple installations.
Warning:
As the function of the pressure relief valve on this water heater is to discharge high
temperature water under certain conditions, it is strongly recommended the pipe work downstream of
the relief valve be capable of carrying water exceeding 93°C. Failure to observe this precaution may
result in damage to pipe work and property.
TEMPERATURE AND PRESSURE GAUGE
The temperature and pressure gauge is shipped loose (within the top cabinet) for field installation and
should be installed within 300 mm of the water heater outlet in an easily readable location.
IMPORTANT:
When installing a new water heater to an old or existing system, it is a requirement that
the system and its equipment be thoroughly inspected and if necessary, drained and flushed with clean
fresh water, before the new water heater is connected. Failure to do this may cause blockages and/or
damage to the water heater which is not covered by warranty.
IF THERE IS ANY DOUBT ABOUT THE SYSTEM, DRAIN AND FLUSH AS A PRECAUTION.
Water Connection Sizes
MVB Model
910500 910750
911000
911250
911500
911750
912000
Water
Inlet/Outlet*
RC2
RC2
RC2½
RC2½
RC2½
RC2½
RC2½
Relief Valve
RC¾
RC¾
RC¾
RC¾
RC¾
RC¾
RC¾
*Water and gas connections on the MVB are NPT threaded and will not seal against ISO 7 (BSP)
threads. The adaptors supplied must be fitted in order to make further connections to the system.
Table 8: Water Connection Sizes
WATER INLET AND OUTLET
All pipe work must be cleared of foreign matter before connection and purged before attempting to
operate the water heater. Use thread sealing tape or approved thread sealant on all fittings.
A disconnection union and isolation valve must always be provided at the inlet and outlet on the water
heater to allow for disconnection of the water heater.
Do not reduce the pipe work size and water heater water connections without allowing for friction loss
which will occur. Low water flow will cause damage to the water heater and system components.
