RV Hydronic Heater Repair



The models ending in "E" were built with engine preheat pump

The models ending in "M" were built with NO engine preheat pump

   Many units have been retrofitted with engine preheat pump



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



This model may also be known as:



Note that the 200 and 500 series use the same components

Changes From Previous Model


Combustion chamber redesigned.


Exhaust pipe goes straight down from bottom of combustion chamber.


Has same footprint as 07x, 08x, 09x and model AHE-450 models.


Set fuel pressure on Webasto to 145#

Part Notes


  • Control Thermostat -   ELE-014-010
  • Electric high limit thermostat - ELE-HLT-322   -or- with terminals crimped on  ELE-ASY-200-HYD
  • Diesel high limit thermostat -  ELE-HLT-322 
  • Control Board -  ELE-PC4-010  This control board will directly replace the 008 and 009 models.  You may have to crimp different (larger) terminals on 12-VDC supply wires.
  • Tank level sensor (float switch) - ELX-01G-ML7  Note that ELX-800-002 - Brass float will not work (there is not enough room in boiler tank for float to operate properly)
  • Zone, stir and engine preheat pumps (are no longer available).  Pump upgrade kit, here: PLE-100-905-FRU
  • (Giant) Radiator cap - PLX-403-000
  • Open zone pumps (no plastic cover)
  • Check valves are outside of the case.
  • NO drain valve
  • Uses ‘clip on’ Low Temperature Cutoff Thermostat - ELE-LTC-505
  • Electric system uses ELX-228-1A1 - Relay, SPST, 12 VDC/30 Amp. Neutral wire is switched through relay and high limit. Upgrade kit available, here: ELE-630-002-HYD
  • Exhaust pipe connects in different location than later models starting with 06x model.
  • Set fuel pressure on Webasto to 135# instead of the 'standard' 145# (exhaust different)
  • Reconditioned Webasto burner - WPE-905-83H-R



Routine service parts and kits - Routine Service Parts      Scroll down page for filter and nozzle packages.



Common Problems


Service Manual


On Aqua-Hot website   HHE-200-07E  Scroll down page in "Discontinued Hydro-Hot Products" section