Rheem MPi 551 Series Owner's Manual And Installation Instructions page 11

TEMPERATURE PRESSURE RELIEF VALVE
This valve is near the top of the water heater and is essential for its
safe operation. It is possible for the valve to release a little water
through the drain line during each heating period. This occurs as the
water is heated and expands by approximately 1/50 of its volume.
Continuous leakage of water from the valve and its drain line may
indicate a problem with the water heater (refer to
Pressure Relief Valve Running"
Warning: Never block the outlet of this valve or its drain line for
any reason.
Operate the easing lever on the temperature pressure relief valve
once every six months. It is very important you raise and lower
the lever gently.
DANGER: Failure to do this may result in the water heater
cylinder failing, or under certain circumstances, exploding.
Warning: Exercise care to avoid any splashing of water, as
water discharged from the drain line will be hot. Stand clear of the
drain line‟s point of discharge when operating the valve‟s lever.
If water does not flow freely from the drain line when the lever is
lifted, then the water heater must be checked. Phone Rheem
Service or their nearest Accredited Service Agent to arrange for an
inspection.
The temperature pressure relief valve should be replaced at
intervals not exceeding 5 years, or more frequently in areas where
there is a high incidence of water deposits (refer to
on page 12).
EXPANSION CONTROL VALVE
In many areas, including South Australia, Western Australia and scaling water areas, an expansion control
valve is fitted to the cold water line to the water heater. The expansion control valve may discharge a small
quantity of water from its drain line during the heating period instead of the temperature pressure relief valve
on the water heater.
Operate the easing lever on the expansion control valve once every six months. It is very important you
raise and lower the lever gently. The expansion control valve should be checked for performance or
replaced at intervals not exceeding 5 years, or more frequently in areas where there is a high incidence of
water deposits.
"Temperature
on page 17).
"Water Supplies"
11
REGULAR CARE
lift until water
drain
flows from the
drain line –
line
lower gently
water
heater