© 2011
D 406 - 12/11
46 of 48
Symptom
Look For...
Corrective Action
LCD display is
off
Fuse holder
Control power supply has a 24 V (ac) fuse which if blown, requires replacement.
Power to control
Use electrical meter to measure 24 V (ac) voltage on input power R and C
terminals.
No DHW tank
heating
DHW Call on LCD
If a DHW call is present, the control is aware that the DHW tank requires heat.
DHW tank reading
Ensure the DHW tank temperature is accurate and replace DHW Sensor if
necessary.
Boiler symbol on
LCD
If the boiler symbol is on the LCD, there is a problem with the boiler. Ensure the
boiler aquastat manual limit is reset to the on position.
DHW pump symbol
on LCD
If the DHW pump symbol is on, check to ensure the DHW pump is in operation by
checking for pump vibration or voltage on the pump wiring terminals.
DHW pump in
operation
If DHW pump and boiler are operating, the system may require the boiler system pump
to operate to heat the DHW tank. Ensure the DHW Mode setting is set correctly.
No central
heating
Heat pump symbol
on LCD
If the heat pump symbol is on the LCD, there is a problem with the heat pump. Check
the heat pump for faults or reference the manufacturers` literature.
“MAX” symbol on
LCD
The heat pump is prevented from operating due to high return water temperature.
Adjust the HP RETURN MAX setting to the heat pump manufacturers’ recommended
maximum return water temperature for heating.
WWSD symbol on
LCD
Warm Weather Shut Down (WWSD) is an energy saving feature that prevents central
heating during the summer. Ensure the outdoor temperature reading is accurate and
replace outdoor sensor if necessary. WWSD setting can be increased if heating is
required.
Tank, Mix or Boil
Calls on LCD
If there are no Tank, Mix or Boil Calls, there are no thermostats calling for heat.
DHW Call on LCD
During DHW tank heating, the central heating may not be heated by the boiler.
System in AWAY
During AWAY, the thermostats operate at a lower temperature. Locate a ‘User Switch’
and set to Normal to resume heating.
MODE setting
The mode of the 406 can be set to Auto, Cool, Heat, Backup, or Off. For central
heating to occur, ensure the mode is set to either Auto, Heat, or Backup.
No central
cooling
“MIN” symbol on
LCD
The heat pump is prevented from operating due to low return water temperature.
Adjust the HP RETURN MIN setting to the heat pump manufacturers’ recommended
minimum return water temperature for cooling.
Cool outdoor air
temperature
The heat pump is prevented from operating due to low outdoor air temperature.
Adjust the Y COOLING CWSD setting to an appropriate outdoor temperature to
stop cooling.
Tank or Mix Calls on
LCD
If there are no Tank or Mix Calls, there are no thermostats calling for cooling.
System in AWAY
During AWAY, the thermostats operate at a higher temperature. Locate a ‘User
Switch’ and set to Normal to resume heating.
MODE setting
The mode of the 406 can be set to Auto, Cool, Heat, Backup, or Off. For central
cooling to occur, ensure the mode is set to either Auto or Cool.
Boiler short
cycling
Burner symbol
cycling on and off
Backup using the variable speed injection pump (VAR) requires the balancing valve
to be set correctly. Lack of head pressure can lead the injection pump speed to
ramp up and down.
Single zone over
heating
LCD shows zone on
Thermostats have a differential of +/- 1.5°F of the temperature setting. Due to the
display rounding numbers up, heating can appear on when the temperature is 2°F
above the setting. This is normal operation.
LCD shows zone off
Ensure zone valve terminals measure 0 V (ac). Measuring 0 V (ac) indicates
mechanical zone valve may have failed in open position. Measuring 24 V (ac)
indicates control relay may have failed.
Single zone
under heating
LCD shows zone on
Ensure zone valve terminals measure 24 V (ac). Measuring 24 V (ac) indicates
mechanical zone valve may have failed in closed position. Measuring 0 V (ac)
indicates control relay may have failed.
LCD shows zone off
Check for calls
Frequently Asked Questions
