The Bosch Therm 520HN and the Bosch Therm 520PN Tankless Water Heaters are the direct replacements for the older Aquastar model heaters such as the 170VP, 125VP, 125B, 125X, 125HX and the 1600H & 1600P as well as the Bosch Protankless 425HN and 425PN.
Just like these older Bosch AquaStar tankless water heaters, the Bosch Therm 520 series are 117,000 BTU heaters that do not require any electricity. The Bosch Therm 520 PN has a standing pilot light and the Bosch Therm 520 HN uses Bosch's patented Hydrogenerator technology to start the water heater without electricity whenever the unit senses a demand for hot water.
Please be aware that if replacing an older model 125 series heater and the heater was vented out the sidewall of the home using the AQ1 powervent then you would need to order the new 520 series replacement heater and the new AQ4 powervent kit. The new model Bosch Therm 520 heaters are not compatable with the older AQ1 power vent kit and the AQ4 does require electricity.
The Bosch AquaStar 125B was designed to be vented up through the roof with 5" B-Vent. The Bosch 125B was replaced by the Bosch 1600P and the Bosch 425PN. All of these heaters were replaced by the 117,000 BTU Bosch Therm 520 PN.
The Bosch AquaStar 125HX was designed to be vented up through the roof with 5" B-Vent. The Bosch 125HX was replaced by the Bosch 1600H and the Bosch 425HN. All of these heaters were replaced by the 117,000 BTU Bosch Therm 520 HN.
GlobalTowne is an Authorized Bosch Distributor.