MHG Heating ThermSelect, Assembly, Commissioning And Maintenance Instructions

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9. Troubleshooting
ThermSelect®
74/100
Troubleshooting
Fault Cause Remedy
Defect on input
side (LP fault)
Ventilator(s) is/are not running Check fuse, check relay
Check control signal 0-10 V
Heat source pump not running Check fuse, relay and pump
Condenser dirty/iced over Clean condenser, initiate thawing;
check temperatures on condenser
Expansion valve incorrectly set / defective Request factory service
Refrigerant circulation interrupted (shut-off
valve closed, filter dryer dirty). Request factory service
Water inside the refrigerant circulation (hu-
midity indicator in the refrigerant sight glass
yellow/red) Request factory service
Temperature of the heat source too low -15°C application limit reached
Water in the condenser too cold (below
20 °C) Pre-heat heating water electric heating insert
Quick temperature change in the condenser Check volume flow
Low refrigerant level (see sight glass) Request factory service
Controller parameter set incorrectly Set parameters according to guide
Contact interrupted Check LP switch wiring
Manual unlocking necessary if the low pres-
sure monitor triggers.
Defect on input
side (HD fault)
Heating pump is not running Check fuse;
check relay/ contactor K4;
Check running wheel for dirt build-up
Water circulation interrupted or insufficient
(possibly not enough heating circuits open) Check water circulation in heating system;
open radiator valves or positioning drives
Heating water temperature too high
No heat discharge, e.g. heat exchanger in
the boiler of the service water heater is too
small Check technical specifications for service wa-
ter heater, min. heat exchanger surface
0.2m²/kW heat output
Air in water circulation Vent the water circulation
Dirt catcher clogged Clean dirt catcher
Circulation pump defective or wrong rotation
direction Check circulation pump and rotate/replace, if
necessary
Controller parameter set incorrectly. Set parameters according to guide
Manual unlocking may possibly be neces-
sary if the high pressure monitor triggers.