Morco FEB-24E - Troubleshooting DHW Not Working

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3. DHW DOES NOT WORK BUT CH DOES.
When you open any
hot tap is there a flow
of at least 2 l/min
through the boiler.
Check for blockages in
the cold water inlet
and that supply is not
restricted.
OUT
IN
With the hot tap running does
the hydraulic 3 way valve port
into DHW mode, releasing the
DHW micro switch tip to start
the DHW ignition sequence?
Check for 13v dc at J4 on
PCB, brown/blue.
Check that the boiler is not cross
connected on the hot/cold inlet. Non
activation of 3 way valve can be caused by
blockage within the unit (venturi) or
diaphragm failure, rectify fault or replace
hydraulic unit, (see notes on thermostatic
shower mixing valves before repairing or
replacing 3 way valve).
13v dc at J4 on PCB
brown/blue.
Replace DHW micro switch.
Temporarily connect a
DHW thermistor (screw in
type), does the boiler work?
Replace the DHW thermistor.
Are the wiring connections
and values of the DHW
variable resistor on the
front panel control PCB to
the main PCB ok?
Remake the connections
from the front panel
control PCB to the main
PCB.
Replace the main PCB.
No
Yes
Yes
No
No
Yes
Yes
No
Yes
No