Heat Sink Paste Application for Bosch Electric Tankless PCB Board Replacement

This will cover a little more in depth application of the heat sink paste that needs to be applied to the back of the triacs on the pcb board for the Bosch High KW electric tankless water heaters.  When you are replacing the PCB control board on a Bosch electric tankless water heater for the high KW units such as the AE-115/WH17 or the AE-125/WH27 you want to make sure to apply the heat sink paste that comes with the new PCB board.

The heat sink paste will come in a small syringe type applicator and a small amount will need to be applied to the back of each triac.  The triac's are the small black squares to the left of the PCB board labeled by the letter G in the picture below.  The Bosch AE-115/WH17 will have 4 small black triac's to the left of the PCB board and the AE-125/WH27 will have 6 small black triacs to the left of the PCB board.  There are service bulletins that show the PCB board replacement and heat sink application.  Bosch Service bulletin EP-22 will show the PCB board replacement for all the newer high KW units with polymer modules.    Bosch Service bulletin TWH-E2-22 will show the PCB board replacement for all the older high KW units with copper canisters.

For further questions or to purchase a new PCB control board visit this link:

http://www.globaltowne.com/shop-by-category/bosch-tankless-water-heaters-spare-parts.html?spare_part_type=162

or please call GlobalTowne at 888-726-9752 or visit our website.

PCB Boards for Powerstar AE-115 & AE-125 Electric Tankless

Bosch has made many upgrades and improvements to the Bosch Powerstar AE-115 and Powerstar AE-125 electric tankless water heaters.  One of the main improvements is in the Printed Circuit Board (PCB) that basically controls the heater.  Below is a list of the older and newer Powerstar AE115 & AE125 PCB board part numbers and the cutoff dates.

Older Powerstar AE-115 & AE-125 with Copper Canisters and serial number BEFORE #59:
AE-115 PCB Board - #93-793777
AE-125 PCB Board - #93-793778

Powerstar AE-115 & AE-125 with Polymer Modules and serial number 60 through 107:
AE-115 PCB Board - #93-793843
AE-125 PCB Board - #93-793844

New Powerstar AE-115 & AE-125 with Polymer Modules and serial number 108 and above:
AE-115 PCB Board - #8738701732 (87387017320)
AE-125 PCB Board - #8738701738 (87387017380)

New Bosch Powerstar AE-115 & AE-125 Electric Tankless

Bosch Powerstar AE-115 & AE-125 Electric Tankless Water Heaters

Ideal for replacing your electric storage tank water heater. The Bosch Powerstar AE-115 & AE-125 electric whole house tankless water heaters are compact and powerful and can be installed virtually anywhere inside the home. Advantages include endless hot water, reduced electricity costs and substantial space savings.

Designed to replace a 20 - 40 gallon electric tank. The Bosch Powerstar AE-115 & Bosch Powerstar AE-125 electric tankless water heaters are built to last. Each heater module is protected by an electro-mechanical thermal cut-out. If the temperature of any of the heater modules gets too high (over 195 degrees), then the cut-out will trip and cut the power to that heater module. If the cut-out trips, it must be reset while the circuit breakers are off. If you are not comfortable or qualified to perform this task, consult the original installer or a licensed electrician. This cut-out will only trip in exceptional circumstances. They have Plastic Polymer Modules and brass fittings. These small electric tankless water heaters can be installed virtually anywhere in the home and, of course, produce an endless supply of hot water.

There are many changes in the new Powerstar AE-115 and the AE-125 compared to the older models Powerstar AE-115 & AE-125.

The improvements for the New Bosch Powerstar AE-115 & AE-125 are:

• The units overall height is shortened by 3 inches due to reconstruction and placement of the main PCB board in the bottom of the unit.  (AE115 PCB Board #8-738-701-732 (87387017320), AE125 PCB Board #8-738-701-738 (87387017380).  These PCB boards are required for all new Powerstar units with serial number beginning with 108 and higher.
• The Heating element assembly modules inside the unit have been redesigned to change the flow of the water in the modules to a different angle so as to not allow the mineral deposits to build up on the elements.
• There has been new single triac and dual triac PCB boards attached to the top of the heating modules as to give the heater more sensibility and maintain a more consistant heat.  (Single Triac PCB #8-738-701-733, Dual Triac PCB #8-738-701-723).
• The Thermal Cutouts on the top of the heating modules have been redesigned to trip at a little lower temperature of 195 degrees F to keep the elements from being damaged and overheating and hurting the piping and modules.

The minimum activation rate required for the unit to activate. (Activation rates: AE-115 = 0.6 GPM, AE-125 = 0.8 GPM).

The AE115 & AE125 are designed for cold potable water only. These water heaters are not designed for preheated water or recirculation applications. Increase flow rate where ever possible if water is coming out too hot.

Verify incoming water supply is at least 30psi. For people on well systems, the recommended pressure range is 30-50psi.

Maximum flow rates for each unit are as follows. AE-115 = 2.3gpm, AE-125 = 3.5gpm.

Descaling Powerstar AE-115 & AE-125

The electric tankless water heaters, Powerstar models AE115 and AE125 are high kilowatt electric tankless heaters that heat water on demand as the water passes through them. The modules inside consist of coiled elements that heat the water. The heating elements produce extreme heat inside the modules to heat the water on demand.

The heat that is produced by the heating elements in the modules sometimes counteracts with the mineral deposits in the water. If there is a high mineral content due to a hard water area then these mineral deposits known as "scale deposits" will over time attach themselves to the heating coils inside the modules.

All Bosch Powerstar electric tankless water heaters should never be descaled with any type of solution such as vinegar, muriatic acid, etc. The use of descalants flushed through the heater does not have much effect on the mineral deposits attached to the elements. Another point of trying to flush descalant through an electric tankless heater is that it will loosen some of the mineral deposits in the heater and will have a damaging effect on the flow transducer and other parts inside the tankless heater that detects the flow of water and will interrupt the signal to the circuit board itself.

The best protection against mineral deposits (scale) forming on the coils in the electric tankless heater is to check the quality of the water in your area before installing and if the water has a high mineral content then it is recommended to install a water softener or scale stopper system. The water softener or scale stopper will filter out almost all of the minerals and treat the water so the electric tankless water heater will have a longer life with less minerals building up inside.

PCB Control Boards for Powerstar AE-115 & AE-125

The PCB control board (Printed Circuit Board) is a thermostatically controlled circuit board that allows the electric tankless water heater, model AE115 & AE125 to be manually controlled by a temperature dial that would range in temperature from 86-131 degrees. The PCB in conjunction with a flow transducer enables the PCB to turn on additional elements in the heater as necessary depending on the amount of gallons per minute (gpm) flowing through the heater.

The PCB would recognize many factors in the function of the heater to maintain a steady temperature and all of this is determined on where the temperature knob is set too, the gpm flowing through the heater and the temperature of the incoming ground water.

To obtain the maximum heating potential of the Powerstar electric tankless water heater, it must be wired correctly and have the full required voltage to the unit. The Powerstar AE115 would require 2 independent double pole 40 amp breakers wired with 8 gauge wire and could draw a maximum of 80 amps at full flow through the heater. The Powerstar AE115 would require the home to be supplied with a minimum of a 150 amp service. The Powerstar AE125 would require 3 independent double pole 40 amp breakers wired with 8 gauge wire and could draw a maximum of 120 amps at full flow through the heater. The Powerstar AE125 would require the home to be supplied with a minimum of a 200 amp service.

The maximum inlet water temperature allowed into the heater is 86 degrees Fahrenheit.

The Powerstar AE-115 & AE-125 have had many upgrades and engineering improvements over the years. In January 2007 the AE-115 & AE-125 went from having copper canisters that contain the heating elements to an upgraded Polymer module. The PCB control board was also upgraded to maintain a more steady temperature that works with the heating elements in the polymer modules.

Below are the designated PCB control board part numbers for the units before and after 2007.

Before 2007 with serial #60A 00000 or lower:
Powerstar AE-115 PCB with copper can units, part #93-793777
Powerstar AE-125 PCB with copper can units, part #93-793778

After 2007 with serial #60A 80000 or higher:
Powerstar AE-115 PCB with polymer units, part #93-793843
Powerstar AE-125 PCB with polymer units, part #93-793844

POWERSTAR AE-115 AND AE-125

The Powerstar Electric Tankless Water heaters model Powerstar AE-115 and Powerstar AE-125 are designed for whole house use and would replace a traditional 40 gallon electric tank heater that will provide endless hot water throughout the home. With two powerful and compact models to choose from, AE-115 or AE-125 it will fit just about anywhere and is built to last.

These 2 Powerstar units have specific power requirements as the AE-115 would require the home to have a minimum of a 150 amp service to the home and would require 2 double pole 40 amp breakers wired with #8 gauge wire as the unit can draw up to 80 amps when at full usage. The AE-125 would require the home to have a minimum of a 200 amp service to the home and would require 3 double pole 40 amp breakers wired with #8 gauge wire as the unit can draw up to 120 amps when at full usage. Please view this link for the AE115 and AE125 power requirements:

The Powerstar AE-115 & AE-125 models have had many new upgrades over the years. The biggest upgrade was that the canisters inside the tankless heater used to have copper canisters and then in 2007 they were upgraded to poly tanks that are more durable and would handle expansion and contraction of the heat better and would be less susceptible to mineral buildup.

The Powerstar AE-115 is designed for 1 major application at a time and is recommended for installation in homes that are in the southern regions of the United States as the incoming ground water is warmer giving the heater a higher temperature degree rise.

The Powerstar AE-125 is designed for 1 major application and 1 sink at a time and is recommended for installation in homes that are in the northern region of the United States where the incoming ground water is cooler and this heater will be able to give a higher degree temperature rise.

The Manufacturer of the Powerstar AE-115 & AE-125 require that there must be at least 3-4 feet of copper water piping coming from the units on the hot and cold water side before attaching to any pex piping as this is due to thermal expansion.

The Powerstar AE-115 & AE-125 are both UL & CSA approved.

AE 115 and AE 125 Heaters and control

Many times we have been asked if the Bosch AE115 and Bosch AE125 can accept pre heated water. The answer is no.

The reason lies in how the unit controls the temperature. These large KW whole house tankless water heaters are designed to take cool water and heat the water to shower temperature as the water passes through the heater. The heater turns on as flow is detected and turns off when the water flow ceases.

There is a temperature sensor on the inlet water pipe (cold) and a sensor on the outlet pipe (hot). The switch that turns the heater on is a solid state style switch or SCR switch. This type of switch has no moving parts and is very reliable. However, SCR or solid state switches generate heat as they switch electrical current. To cool these switches, they have been located on the inlet (cold) water inlet. So the copper pipes act as a heat sink for the SCR switches. If hot water is passed through the pipes and the heater turns on the SCR switches could over heat and FAIL.

Call us for any applications involving the need to have pre-heated water through a tankless heater. We can provided gas and electric heaters for floor heating or other applications needing to circulate warm or hot water.

Visit Globaltowne.com

Whole House Electric Tankless Water Heaters

Bosch offers two Whole House Electric Tankless Water Heaters: the PowerStar AE125 and the PowerStar AE115.

A perfect alternative to the electric tank water heater, the PowerStar electric tankless water heaters are designed to replace a 40-gallon tank and provide endless hot water throughout the home.

These compact water heaters (15.5" x 15.25" x 4.5") will fit just about anywhere and are built to last!

The AE125 provides 4 GPM at a 45 degree F temperature rise. It is a single phase 27kW heater running on 240 volts. It requires 3 x 40 AMP breakers and Bosch recommends a minimum 200 AMP service to your house.

The AE115 provides 2.6 GPM at the same 45 degree F temperature rise. It is a single phase 17kW heater running on 240 volts. It requires 2 x 40 AMP breakers and Bosch recommends a minimum 150 AMP service to your house.

Bosch has provided the following map as a guideline to where the AE115 should be installed:


When the AE125 is installed in Canada the AE Canada Kit is needed. The AE Canada Kit for the PowerStar AE125 is a 6 way terminal block for use when installing the AE125 in Canada. In Canada, the AE125 requires a 120A 240V AC single phase supply protected by a 120A double pole circuit breaker.

Steve