Laars LMH Installation And Operation Instructions Manual

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Laars LMH Installation And Operation Instructions Manual Manual pdf 29 page image

Mascot II Boilers and Water HeatersPage 278.2 Ignition Control- Sequence of Events1. Call for heat2. Safety chain check3. Fan starts.4. Prepurge timer is started.5. Pre ignition time of 2 seconds to check the flamesensor operation and status.6. Trial for ignition period, 4 seconds. The directspark ignition switches to constant spark for threeseconds, during which time the gas valve is open.For the last second of the ignition period directspark is de-energized and the flame sensor checksfor established flame. If flame is sensed the controlenters "Run" to satisfy the demand. If flame isnot established the control enters a retry, startingfrom step 2. If flame has not been established inthe appropriate number of retries the control willlockout with a 109 error code.7. Call for heat complete8. Gas valve off9. Fan and pump over run times active to purge thesystemThe sequence is the same for DHW or CentralHeat modes. Upon a call for Central Heat, the 3-wayvalve will shift position, allowing boiler water to enterthe building's heating loop.8.3 Modulation ControlThe control uses a PID algorithm to adjustthe firing rate of the boiler as the control point isapproached. The goal of the control is to operateat a minimum firing rate to match the load on theappliance. The burner modulates to achieve the setpointtemperature, away from the actual off point.8.4 Pump ControlThe boiler pump is active anytime there is a callfor heat applied to the control. When there is a centralheat call supplied the system pump relay is active. Ifthere is a DHW call supplied while the central heatcall is active the system pump turns off. This happensbecause of domestic hot water priority, which forces thecontrol to satisfy the domestic water demand prior to thehydronic demand. When the last heat demand is satisfiedthe boiler pump enters an overrun time.8.5 High LimitThe control uses a dual thermistor sensor tomonitor the Mascot II's maximum temperature. Thehigh limit sensor is installed in the outlet water. A dualthermistor sensor is used, so that the two temperaturescan be monitored and compared to confirm accuracy.The control will automatically reduce the firing of theMascot II to prevent the high limit from tripping. Thehigh limit setpoint is not adjustable.8.6 Stack TemperatureThe stack temperature is a dual thermistor sensorand is limit rated. The control compares each of thetemperature readings to determine accuracy. The stacksensor is used as a limiting feature to avoid excessivetemperatures in the venting.8.7 Domestic Hot Water TemperatureThe domestic hot water temperature sensor is usedto control DHW temperature. The DHW setpoint can beadjusted through the USER menu structure.DHW setpoint is displayed during DHW mode.For LMH model, an aquastat will be used in lieu of asensor to control temperature of an indirect tank.8.8 Lead Lag / CascadingLead Lag/Cascading allows multiple boilers to beconnected together and controlled from one commonsensor input. Up to 8 boilers can be connected togetherin a single system. To setup Lead/Lag or cascadingoperation there are several settings in the "setup"menu structure that must be adjusted for the specificinstallation, each is covered in the following sections.8.8.1 Lead Lag SetpointThe lead lag setpoint is set from the "user"menu using the "LL" variable. This is the temperaturethe boiler is attempting to maintain at the systemsensor. This setting doesn't control the boiler outlettemperature, so the water temperature at the boileroutlet may be much hotter than the system temperaturesetpoint. Adjust the LL setpoint to the desired operatingtemperature of the system.8.8.2 Lead Lag Master/Slave SelectionIn the SETUP menu structure, the "LL" menuallows the lead lag system to be turned on and the boilerto be configured as a master or slave control. In eachlead lag system there can only be one master control, soproper selection is important to avoid operating issues.To set the boiler to lead lag "master" operation the LLmenu should be set to "LDR". To set the boiler to slave,"SLA" should be selected.8.8.3 Lead Lag AddressThe Lead Lag address must be set for each boilerconnected to the lead lag system. Each boiler musthave a unique address selected for the system to workproperly. Typically, the lead or master boiler should beset to address one and the remaining boilers should beset to values 2–8 depending upon how many boilers areinstalled in the system.8.8.4 Lead Lag HysteresisThe lead lag system uses a hysteresis value setin the setup menu, called, "HS". The hysteresis andsetpoint values control the on and off points of theboiler. If the lead lag setpoint is adjusted to 120°F witha hysteresis value of 5°F the boiler will turn off whenthe water temperature reaches 125°F and will turn back