The following service bulletins are arranged chronologically with the most current at the top of the list.
Models 900 and 900 2005 Gas Fired Switch Heater Troubleshooting Aid Flowchart.
Switch Heater Solenoid Valves Inspection and Maintenance Inspection and Maintenance Procedures Hovey Mark 6, Mark 7, and Hellfire 900 solenoid gas valves require periodic inspection and maintenance, as per procedure
Proper disabling of snowdetection.
HELLFIRE 2005 series switch heaters equipped with the EMS option and configured for continuous operation will time out, after the duration of the RTC Timer setting, when requested by RTC only.
Set up and safe operation of heaters installed with fiberglass switch covers.
All heaters manufactured between 2000 and 2002. Leaking thermostat cover, Hovey part number 17320, causes nuisance shut downs due to false high limit thermostat alarm.
Flame rods. All heaters manufactured between 1997 and 2001. Occassional nuisance shut downs due to loss of flame signal.Water can accumulate in the seam of the two piece flame rod ceramic creating a short circuit between the rod and ¼ NPT mounting bushing (ground).
Hellfire 400. Incorrect wiring of motor thermal overload.
Yardmaster. The air pressure switch measures the difference in pressure between the fan and electrical enclosures. Air leakage, caused by an undersized gasket on the top of the electrical panel, into the electrical enclosure and insufficient venting of the enclosure with the access panel in place, reduces the differential pressure below the setpoint and keeps the burner from igniting.
Precipitation detector. The original grid surface temperature setpoint was set at 10 degrees centigrade. At this temperature the grid melts snow, but the moisture remains too long before evaporating, therefore turning the heater on with only a light dusting of snow and running the heater for an excessively long time once the snow has stopped.
All Switch heaters. Plans issued by UP and CN headquarters to the field show incorrect wiring between the signal bungalow and the heaters. A separate source of 120Vac is supplied from the signal bungalow to terminal A1 of the heater. Such wiring creates a personnel safety hazard. With the heater requested by dispatch the electrical panel is energized, with 120Vac, the heater will operate, with the local panel circuit breaker opened.
MARK 6 Small enclosure. Over the course of the 97/98 winter a problem with the MARK 6 Small enclosure railway switch heater's solenoid operated gas valve has been identified, causing the heater to fail on start-up.
Frog Tieduct. A quantity of 22, #20 and 1, #30 MPF tieduct systems, Hovey part numbers 15273 and 15296 respectively, delivered to the UP railroad since November 97 have a design error which leaves a 1/4" gap between the center of the tieduct and the MPF baseplate.
Precipitation detector. We have identified a detector cone and grid heater wiring error. Detectors with this error will not melt and detect snow.
MICRO Mark 5. As a result of investigating repeated heater failures experienced on some MICRO Mark 5 switch heaters this winter, we have found that excessive moisture accumulation on the flame rod, grounds the flame signal and simulates a flame failure. Using a silicone spark plug wire connector insulates and prevents grounding of the signal to the cold side of the burner.
Mark 6 small enclosure. As a result of investigating repeated flame failures ("Lockout 28 pilot flame failure" and "Lockout 19 main flame failure") experienced on some Mark 6 small enclosure switch heaters this winter, we have found that excessive moisture accumulation on the flame rod, grounds the flame signal and simulates a flame failure. Using a silicone spark plug wire connector insulates and prevents grounding of the signal to the cold side of the burner. We have received reports, that heaters have been found shutdown and locked out on "air switch failure" with ice blocking the air switch tube.
MK6 Bungalow enclosed. Switch Heaters built for Union Pacific Railroad and shipped Aug 24/94 and Sept 7/94, are experiencing failures of the pin which locks the extendable foundation legs. This poses a potential Safety Hazard. Click here for PDF
Heater duct work. It has been brought to our attention that cross duct gaskets supplied with switch heater units prior to Sept 17/92, are not providing the required electrical insulation. There are two key locations where electrical isolation is required. One occurs where the end and cross ducts are joined. The purpose of this joint is to electrically isolate the two rails in the event of the ducting coming in contact with them. The other isolation has to occur between the bungalow and the first rail.