Bosch AquaStar 125B Replaced by Bosch Therm 520 Series

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.

FX HOOD Terminator

GlobalTowne still has a few of the Bosch FX Termination Hood's (FXHOOD) left in stock.  These FX Hood's were used to vent the older Bosch 125FX and 240FX gas tankless water heaters.  The FX Hood is a 4" diameter termination hood for venting out the sidewall.  The FXHOOD had a flapper inside to keep the cold out when the unit is not in operation. The FX Hood is made of galvanized metal.

The current replacement for the Bosch Aquastar 125FX is the Bosch Therm 520PN with an AQ4 side wall vent kit.

Please call GlobalTowne with any questions or to order at 888-726-9752

Water Valve Part Numbers for Older Bosch Aquastar 125 Series Gas Tankless Water Heaters

All of the older Bosch Aquastar 125 series model gas tankless water heaters are no longer made.  The Aquastar 125 series were distributed by Controlled Energy Corporation (CEC) over 8 years ago and CEC has sold the company to Bosch.  Below is a list of all the water-valves and their part numbers and all these valves are sold through GlobalTowne.  Please be aware of the serial number cutoffs for some of the water valves as they have changed over the years.

Aquastar 125B Water Valve: for heaters with serial number beginning with 380 or below: 8707002499 (8-707-002-499, 87070024990)

Aquastar 125B Water Valve: for heaters with serial number beginning with 381 and above: 8707002649 (8-707-002-649, 87070026490)

Aquastar 125BL Water Valve: 8707002478 (8-707-002-478, 87070024780)

Aquastar 125BS Water Valve: 8707002393 (8-707-002-393, 87070023930)

Aquastar 125BO Water Valve: 8707002708 (8-707-002-708, 87070027080)

Aquastar 125X Water Valve: 8707002810 (8-707-002-810, 87070028100)

Aquastar 125FX Water Valve: for heaters with serial number beginning with 380 or below: 8707002810 (8-707-002-810, 87070028100) This part replaces part number 8707002534.

Aquastar 125FX Water Valve: for heaters with serial number beginning with 381 and above: 8707006361 (8-707-006-361, 87070063610)

Aquastar 125HX Water Valve: 8707002649 (8-707-002-649, 87070026490)

Please visit our website at www.globaltowne.com for all spare parts.  Some of the Bosch Aquastar replacement parts are not listed so please call us at 888-726-9752.

Replacing a Bosch Aquastar 125FX with a Bosch Therm 830ES

The older Bosch Aquastar model 125FX came in either Natural Gas (NG) or Liquid Propane (LP) and was 117,000 BTU and was a direct vent unit that was good for one major application at a time.  The 125FX had electronic ignition and was fan-assisted and took its combustion air from the room it was installed in.  The heater had a built-in fan so the heater could be vented right out the sidewall of the building.  The Aquastar 125FX had to be vented with 4" sealed stainless steel venting going a maximum of 15' out the sidewall of the building into the FXHood.  The FX Hood was a termination hood specifically designed for the 125FX and had a built-in flapper to keep cold air from penetrating the vent pipe and freezing the heater.  The Bosch Aquastar 125FX is discontinued now and has not been made for over 8 years or so.  One of the closest replacement models for the 125FX would be the new Bosch Therm 830ES.

Bosch Therm 830ES

The new Bosch 830ES comes in either Natural Gas (NG) or Liquid Propane (LP) and is 175,000 BTU which is slightly more BTUs than the older 125FX.  The Bosch 830ES needs a minimum of a 3/4" gas line and has 3/4" water connections also.  The 830ES is a sealed unit and takes its intake air from the outside using 3" PVC.  The unit is vented to the outside using 3" Stainless steel venting and this could be attached to the FX Hood that is already in place using a 3" to 4" increaser (Z-Flex Part #2SVSI0304).  The 830ES is digitally controlled and can go from 100 - 140 degrees F.  See below for more specifications and capacity.

Therm 830 ES	Specifications
Condensing/Non-Condensing	Non-Condensing
Application	Residential or Commercial
Max Input (BTU)	175,000
Min Input (BTU)	19,900
Capacity at 35°F Rise (gpm)	8.3
Capacity at 55°F Rise (gpm)	5.3
Intelligent Cascading	Yes
Min Flow Rate	0.5 gpm
Temp Range (°F)	100 - 140
Temp Stability (°F)	+/- 2
Default Temp (°F)	122
Energy Factor	.82
Thermal Efficiency	82%
Installation Options	Indoor or Outdoor (for outdoor, kit required)
Dimensions (w x h x d)	17 7/8" x 31½" x 11¼"
Weight (lbs.)	67
Inlet Connection	¾" NPT
Outlet Connection	¾" NPT
Gas Connection	¾" NPT
Max Water Pressure	150 psi
Min Water Pressure	30 psi
Min NG Presure	3.5" WC
Condensing Heat Exchanger	n/a
Venting Options	Stainless Steel
Vent Maximun Run	61.25'
Energy Star Rated	Yes

Service Bulletins for Older Bosch Aquastar Gas Tankless Water Heaters

Bosch has a series of service bulletins for the older retail model Bosch Aquastar and also the compact models such as the 1600P & 1600H.  These service bulletins can be very helpful with installation questions and when having issues with the Bosch tankless water heater.

Service bulletins can help with fixing an issue or with servicing your Bosch tankless water heater.  Please keep in mind and be safe when working on a gas appliance.  You can also contact Bosch directly or have you service agent contact Bosch technical support at 800-642-3111.

Link to:
G3 Service Bulletins for GWH 2700 ES and GWH 2400 ES

CT Service Bulletins for GWH 1000 P, 1600 P, 1600 H

G2 Service Bulletins for GWH 2400 ES/ESO, 250SX/SXO

AquaStar 38B, 125 Series Gas Tankless

AquaStar VP Series Service Bulletins

 AquaStar 240FX Service Bulletins 

Bosch AquaStar 125X Water Valve Assembly (Conversion Kit)

The Bosch AquaStar 125X Water Valve Assembly Conversion Kit Part number 8707002810 is the 

replacement Water Valve assembly for all Bosch AquaStar 125X tankless water heaters.

This part is also is the replacement Water Valve for Bosch AquaStar 125FX tankless water heaters starting 

with a serial number of 380 or lower.

Bosch Aquastar 125 & WR400 Series Heat Exchanger

The Bosch Aquastar 125 Series Heat Exchanger Part #8705406380 (old part number 8705406235) is the replacement heat exchanger for all Bosch Aquastar 125 series and WR400 series Bosch tankless water heaters (regardless of Serial Number).  Astravan is a company in Canada that use to distribute the older Bosch WR400 series tankless water heaters.

Heat Exchanger Part #8705406380 (87054063800, 8-705-406-380-0) is the direct replacement for the following Bosch tankless water heaters:

125B, 125BO, 125BL, 125X, 125HX, 125FX and the following Bosch ProTankless water heaters: 425EF, 425HN (with serial numbers starting 685 and lower) and 425HNO, WR400-1KV1P23S3100, W400KD5  P23S3100T2, WR400-3K V1B23S3100, WR400-7K  V1G23S3195, WR430-3K  VM1E23S3190, WR430-3K  VM1E23S3195

The Bosch Heat Exchanger Part #8705406380 is NOT compatible with the following models:

125BS, 1600P, 1600H, 425PN, certain Bosch ProTankless 425HN (with serial numbers starting 686 and higher), 520PN, 520HN, WRS400K 1P23S3100T2.

Please call us at 888.726.9752 with questions or to place your order.

Replacing an older 125FX LP with a Bosch 660EF LP

The older Bosch Aquastar model 125FX LP (Liquid Propane) was 117,000 BTU and was a direct vent unit that was good for one major application at a time.  The 125FX LP had electronic ignition and was fan assisted and took it's combustion air from the room it was installed in.  The heater had a built in fan so the heater could be vented right out the sidewall of the building.  The 125FX LP had to be vented with a 4" sealed stainless steel venting going a maximum of 15' out the sidewall of the building into the FXHood.  The FX Hood was a termination hood specifically designed for the 125FX LP and had a built in flapper to keep cold air from penetrating the vent pipe and freezing the heater.  The Bosch Aquastar 125FX LP is discontinued now and has not been made for over 8 years or so.  The replacement model for the older 125FX LP would be the Bosch 660EF LP.

Bosch 660EF LP



The Bosch 660EF LP can be used for a direct replacement for the older Bosch Aquastar 125FX LP.  The 660EF Lp is also a direct vent unit, it is 140,000 BTU and has electronic ignition and is fan assisted to vent right out the sidewall of the building.  The 660EF LP has 3/4" water and gas connections on the bottom of the heater.  The 660EF LP also takes it's combustion air from the area where it is installed.  The 660EF LP is designed for 3" stainless steel venting and has a special 660EF adapter required for the top of the unit to attach the venting to.  You would then need to use a 3" to 4" increaser so you could go to 4" stainless steel venting and can then be adapted to hook up right to the existing FXHood.

If the older Bosch Aquastar 125FX LP was originally installed with 4" galvanized venting and there was no FX hood in place then the installer could use the AQ5EF sidewall vent for the new Bosch 660EF LP.  The AQ5EF sidewall vent kit comes with the 660EF adapter, 3"x90 degree elbow, 3oz tube of high temp sealant, wall thimble, termination box, a 3"x12" piece of stainless pipe and a 3"x18" piece of stainless pipe.



FXHOOD for Bosch 125FX Tankless Water Heater

 The FXHOOOD is required by Bosch whenever a customer installs the Bosch AquaStar 125FX Tankless Water Heater. It is also required for the older 240FX model.

The FX Hood is a horizontal vent terminator with built-in freeze protection for the Bosch AquaStar 125FX and 240FX models as well as the Takagi T-K1 Tankless Water Heater. The FX Hood will prevent cold air from freezing the heat exchanger on the Bosch AquaStar Tankless Water Heaters. The back draft preventer (FX Hood) should be used with all electronic ignition gas tankless water heaters where the outside temperature can fall below 32 degrees Fahrenheit.

The Bosch FXHOOD is doubled-piped so it can be installed next to combustible materials. The face plate is 12 inches by 12 inches and the pipe is 8 inches in diameter with the inner pipe being 4 inches in diameter.

Steve

Bosch 1600H with AQ4 vs. Bosch 125FX with FXHood

If you have just one shower and are looking to vent out of the sidewall, Bosch currently offers two tankless water heater solutions.

The Bosch AquaStar 125FX Propane tankless water heater is a 125,000 BTU input tankless water heater (130,000 BTU for Natural Gas model) that has an electronic ignition system. The 125FX comes with a side-wall vent kit called the FX Hood. This heater is designed to be vented out of the side wall and it cannot be vented up through the roof. The 125FX requires electricity to power the electronic ignition and FXHood.

The Bosch AquaStar 1600H is a 117,000 BTU input tankless water heater that is designed to be vented up through the roof. It uses Bosch's patented Hydro ignition system that automatically starts the ignition process when it senses the flow of water. The Bosch 1600H does not require electricity nor does it have a battery. It also has NO PILOT LIGHT. It does require a 5" diameter Type B double-walled vent of at least 6 feet in height when vented vertically.

The Bosch 1600H can be vented through the side wall using the AQ4 Vent Kit. However, please note that the AQ4 Horizontal Vent Kit DOES require electricity. (The AQ4 Vent Kit can also be used for the Bosch 1600P tankless water heater.)

In summary, Bosch offers two solid tankless water heater options for single shower homes requiring side wall venting.

Steve