RV Hydronic Heater Repair

431 serial number 94180 to 98570

This model may also be known as:


920/431, 920431/12, 920/432, 431


Most of these heaters were 12-volt,

however there were a few 24-volt heaters built.

This model of Aqua-Hot uses 'standard' ethylene glycol coolant (Prestone or equal).  Keep it simple and use the same coolant that is in your engine and generator.



Changes From Previous Model

Part Notes


Thermostats are snap disc thermostats.  When built, there was not electric high limit thermostat installed. 

Upgrade kit for electric wiring and thermostats is here:   ELE-560-024


Diesel Control (Blue Dot) ELE-L08-190

Diesel High Limit (Black Dot) ELE-L08-230

Electric Control (Red Dot) ELE-010-198

Electric High Limit (White Dot) ELE-254-010 (This thermostat was later added to most of these heaters)


3 zones + engine circulation pump PLX-809-200.  Used pump, here:  PLX-809-200-U


1650 watt electric element ELX-2E7-540  Note: that electric element rarely fails! 
Most failures in electric system is electric high limit thermostat.


Mixing valve (complete) PLX-4A8-180 - Rebuild kit PLX-4A8-18R


Radiator Cap - PLX-102-229 or with lever PLX-102-229-L

Routine Maintenance


Replace filter and nozzle when exhaust gets smoky / smelly.  Aqua-Hot recommends yearly routine service.


Pumps develop leaks, which require replacement of "O" rings.  March Pump "O" Ring  You have to remove pump to disassemble it to replace "O" ring.


Radiator cap should be replaced at least every other year (or as often as needed).  PLE-102-229  or Cap with Lever PLE-108-229-L

Recommended Service Parts to Keep On Hand


Filter:  VERIFY FILTER:  Normally one of filters below. 

Webasto - WPX-603-359


Racor R12T  FLE-R12-TRA


Nozzle:  WPX-886-41A


Optional Service Parts to Keep On Hand



Service Manual


AHE-100-02S - On Aqua-Hot website