12
PRECAUTIONS
Where damage to property can occur in the event of the water heater leaking, the water heater should
be installed in a safe tray or suitably bunded. Construction, installation and draining of a safe tray or
bunding should comply with AS/NZS 3500.4 and all local codes and regulatory authority requirements.
The water heater must be maintained in accordance with the Owner’s Guide and Installation
Instructions. Refer to
“Maintenance Requirements” on page 17.
If this water heater is to be used where an uninterrupted hot water supply is necessary for your
application or business you should ensure that you have redundancy within the hot water system
design. This should ensure the continuity of hot water supply in the event that this water heater was to
become inoperable for any reason. We recommend you seek advice from your plumber or specifier
about your needs and building redundancy into your hot water supply system.
HOW YOUR WATER HEATER WORKS
BURNER IGNITION
The MVB incorporates an automatic ignition system. On a call for heat the fan performs a high speed
pre-purge operation to ensure any unburnt gas is cleared from the combustion chamber before rotating
at the speed required for start gas rate.
The water heater primary pump will be initiated and a self-proving flow switch will close when flow is
detected. Other devices in the safety chain must also be closed before an ignition attempt will
commence.
A Hot Surface Igniter (HSI) rod begins to glow and when the temperature reaches the desired set point,
the gas valve is opened. If successful ignition is achieved the burner will operate. For H models only,
the controls will modulate the burner rate depending on the incoming temperature versus the set point.
Once the set point is achieved, the burner will turn off and a post purge function will occur. For W
models, some modulation will occur toward the end of the heating cycle to limit temperature overshoot.
Should successful ignition not be achieved within 4 seconds the automatic flame control system will
shut down the gas valve and the heater will go into lockout and require manual intervention to reset the
water heater.
The MVB incorporates many safety features including:
•
Self-proving air pressure switch
•
Self-proving water flow switch
•
Blocked flue pressure switch
•
Electronic thermostatic control sensing temperature at the water heater inlet, outlet and storage
tank or system flow
•
Auto reset hi-limit thermostat
•
EN298 certified controls, including manual reset hi-limit
•
Dungs double block gas valve
•
Pressure relief valve
