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Section 2.0: Operating Sequence and Failure Modes
The V1 mixing valve blends the cold inlet water with the hot inlet water to produce the set-point
outlet water temperature. If the water temperature out of V1 is high, V4 opens which short
circuits the WWM Diaphragm Actuator reducing the hot water flow to the mixing valve outlet.
If the outlet water temperature is above 95°F prior to activating the system the V4 will short
circuit the WWM Diaphragm Actuator holding the hot water port closed until the outlet water
temperature falls below 85°F. The water supply lines should have pressure regulators installed
as per the factory’s installation instructions. The hot water flow pressure should be slightly
higher than the cold water flow pressure but not more than 10 PSIG higher. Refer to Appendix
#1 for the Station Schematic and Appendix #2 for the Station Flow Chart.
If Vl failed with cold port closed (hot port open)
: only hot water flows to mixing valve outlet.
V4 will open and short circuit the WWM Diaphragm Actuator when the Station outlet exceeds
approximately 95°F, thus closing the hot inlet port on the mixing valve. With the hot port
closed, no hot water can flow to the mixing valve, so the Station outlet is cold water only.
Station will start to cycle hot - cold as the V4 sees cold water.
If V1 failed with hot port closed (cold port open)
: no hot water can flow to V1 mixing valve;
system supplied with cold water only. V1 is probably jammed open with debris.
If Diaphragm Actuator failed retracted (normal mixing mode)
: will not be noticed unless there is
an over-temperature situation or loss of hot water supply to the Station.
If Diaphragm Actuator failed extended (override mode)
: no hot water can flow to V1 mixing
valve; system supplied with cold water only.
If V4 failed closed
: no significance unless V1 also fails or outlet temperature is over 95°F for
more than 15 seconds.
If V 4 failed open
: mixing valve hot port will be closed, so only cold water flows from the
Station. Debris may be stuck to the seat area inside the V 4 not allowing a good seal.
Section 2.1: Normal Operating Sequence For Therm-O-Mix Station
Section 2.2: Failure Modes
Section 2.2.1: V1 Failure Mode
Section 2.2.2: WWM Diaphragm Actuator Failure Mode
Section 2.2.3: V4 Failure Mode
