Laars MASCOT LX, Service Manual

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Mascot LX Service Manual
Three-Way Valve - Combi Units (MLXC)
On a “Combi” unit (central heat plus domestic hot water),
the three-way valve shifts the output flow between the
CH and DHW functions.
Normally the system is set up to give priority to DHW.
That is, when the DHW flow sensor detects a demand
for hot water, the three-way valve is closed and the
output of the Mascot LX is sent to the DHW piping. To
send hot water to the CH system, the three-way valve is
energized.
The priority and the timing can be changed using the
Installer mode - parameters P49, P50, and P28.
P28 Domestic hot water demand blocks system pump
enable/ disable
P49 Priority time for central heat over domestic hot
water.
P50 Priority time for domestic hot water over central
heat.
Normally, priority is given to the DHW function. When
the unit receives a call for DHW, the priority time set by
P50 begins (DHW over CH). If the call for DHW con-
tinues until that timer times out, the unit begins to send
heat to the CH system and the timer set by P49 begins
(CH over DHW).
Normally the valve is operated by a solenoid controlled
by the SIT board. However, the valve also includes a
manual actuating arm which can be helpful during trou-
bleshooting. The table below outlines the valve function.
Valve position Sends water to Arm position
Not energized DHW Down
Energized CH Up
To test the valve, move the actuator arm to check for
free motion. Insert a jumper between terminals 8 and
9 on the high-voltage terminal strip. The valve should
actuate, and you should see the arm move.
Fig. B23-1 - Three-way Valve
Three-way
valve
Manual actuator
arm
B23
Tools and equipment required:
• Adjustable wrench
Replacement procedure:
1. Turn off the power switch on the front of the unit.
2. Shut off the gas supply to the unit.
3. Isolate the boiler and drain it.
4. Disconnect the two wires running to the back of the
unit.
5. Using the wrench, undo the unions on each side of
the valve.
6. Undo the union at the center of the assembly. At this
point you will be able to remove the valve.
7. To reassemble, reverse the instructions listed above.
Check for leaks after assembly.