Descaling My Bosch C1050ES Tankless Water Heater

A few weeks ago I descaled my Bosch Greentherm C1050ES-LP Condensing Tankless Water Heater and it was far easier than I had imagined it would be. The total elapsed time to do the complete job was less than an hour. I took a few pictures as I went through the steps.

The above picture shows the JC Whitlam Flow-Aide Descaler Kit. This kit contains the (2) 5' hoses, the submersible pump, the pump intake filter and one quart of Flow-Aide descaling solution.

The above picture shows my Bosch Therm C1050ES-LP condensing tankless water heater and my Webstone 44443WPR Lead-Free Isolation Valves. I took this photo after I had closed the two yellow-handled main water valves and after I had opened the two service ports. I had to place a bucket beneath the two valves to catch the water that was in the internal piping of the tankless water heater.

The above picture shows the two 5' hoses that come with the Descaling Kit attached to the two service ports on my Webstone Isolation Valves.

The above picture shows the Flow-Aide bucket and descaling solution. I had already put one gallon of cold water in the bucket and mixed in the one quart container of Flow-Aide solution. This descaling solution is non-toxic and bio-degradable.

The above picture shows the submersible pump output attached to the cold water connection on my tankless water heater. The pump is not plugged in yet.

The above picture shows the included intake filter attached to the submersible pump input. This filter prevents any debris from being run through the tankless water heater. The pump is still not plugged in.

The above picture shows the descaling process in action. Here you can see the hose from the hot water connection to my water heater just hanging into the bucket. You can also see that I have plugged the submersible pump into a GFCI protected 110 V power outlet.

I let the descaling process run for about 30 minutes. I then emptied out the bucket and rinsed it out thoroughly. I then put about a gallon of cold water into the bucket and I ran that cold water through my tankless water heater for about 5 minutes just to clean it all out.

Lastly, I disconnected everything and then I closed the two service ports on my Isolation Valves. I then opened up the two yellow handles to let the water flow back into my water heater. When I turned on a hot water demand everything worked perfectly!

Vertically constructed vent stack along the outside of the home

It is not permissible to vent a naturally drafting gas tankless water heater such as the Bosch 520HN, 520PN, 1600H, 1600P, 330PN or the 1000P out and up the side wall of the home.  This is not safe as the exposed venting running up the side of the home will be exposed to the elements and cold.  When the temperature outside gets cold and makes the vent stack cold then the exhaust gases from the Bosch tankless water heater will not properly draft to the outside and can fill the home with carbon monoxide.

The installation manual states: "Horizontally venting to a vertically constructed vent stack along an outside wall of a building is not permissible".  This is also against the National Fuel Gas Code (NFGC).  If a Bosch tankless water heater needs to be vented Horizontally out the sidewall of the building then you would be required to use the Bosch AQ4 Powervent Kit.  The AQ4 power vent kit is designed to activate when the tankless water heater comes on and blow the exhaust gases outside.  The Bosch AQ4 power vent kit can be used with the Bosch 520HN, 520PN, 1600H and the 1600P.  The Bosch 330PN and 1000P cannot be power-vented and must be vented vertically up through the roof of the building.


This rule for venting up the outside of the building also applies to the older Bosch Aquastar 125 series heaters and the ELM VP heaters.  For older gas tankless water heaters that were installed and vented up the outside of  the building they would want to have a chase built around them and box the venting in.  Please always be aware of the minimum venting clearances for all venting material.  Please see the before and after pictures below of a vent stack running up the outside of the home.

Incorrect Vent Stack

Corrected Vent Stack

Bosch Therm 520HN, 520PN & 330PN being Phased Out

Bosch Thermotechnology has recently announced that the Bosch Therm 520HN, Bosch Therm 520PN and the Bosch Therm 330PN will be phased out as of April 2015.  Bosch Thermotechnology will not be manufacturing anymore of these units after April 2015.  Globaltowne will still be selling the Bosch Therm 520HN, 520PN and 330PN for as long as we have the stock.  These units are being phased out due to a requirement for all gas appliances from the Dept of Energy that states they have to have a minimum of an 82% thermal efficiency and the 520's & 330 PN are only 81%.

Impact on the Homeowner

The homeowner will have to deal with increased product and installation costs. In some cases, the water heater will have to be re-located to operate properly, or mitigate noise. While the operating cost of the new water heaters will be less because of their increased energy efficiency, it is likely that the maintenance costs will increase because of a more complex design, and the integration of electronics, blowers, fans, condensers, etc.  In some cases, the performance of the new water heater in terms of hot water deliverability will be less than the model which was replaced.

The Bosch Therm 520HN and the Bosch Therm 520PN are direct replacements for the older Aquastar model heaters such as the 170VP, 125VP, 125B, 125X, 125HX and the 1600H & 1600P.  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 replacement heater and the new AQ4 powervent kit.  The new model Therm heaters are not compatable with the older AQ1 powervent kit.

The Bosch Therm 330PN is a direct replacement for the older Bosch 80VP, 38B and 1000P units.  These units are too small and cannot be powervented.

New Ariston "S" Series Replacement Parts

UPDATE 08/17/2023

Bosch Thermotechnology has recently changed the part number for the Bosch GL6+S/GL8TiS/ES8 Thermostat.  The old part number was 87387044420 and the new part number is 8738711261.  GlobalTowne carries this thermostat in stock and can be found at the link below:

GL6+S/GL8TiS/ES8 Thermostat 8738711261

GlobalTowne.com sells user replaceable spare parts for the New Ariston "S" Series Line of mini-tank electric water heaters.  Be sure to buy the correct parts -- one set of parts works for the New Ariston GL2.5S and GL4S models while another set of parts works for the Ariston GL6+S model.

For the Ariston GL2.5S and Ariston GL4S electric mini-tank water heaters we sell the replacement for the sacrificial Anode Rod #87387044470 (Old part #574305). This part can be used for the Ariston GL2.5/GL2.5S, Ariston GL4/GL4S, Airston GL2.5Ti/GL2.5TiS, GL4Ti/GL4TiS and Ariston ES2.5/ES4  mini-tank water heaters as well as for the now obsolete Ariston models P10S and P15S.

We also sell the Ariston GLSKIT which contains the sacrificial anode rod for the Ariston GL2.5S/GL4S Series (#87387044470) as well as the heating element (#87387044390) and the GLS gasket (#87387044500). This Kit can be used for the Ariston GL2.5S, Ariston GL4S, Airston GL2.5TiS, Ariston GL4TiS, ES2.5 and ES4 mini-tank water heaters.

We sell the Ariston GL6+S KIT which includes the element, anode rod, gasket and bolts.  This kit can also be used for the pro series heater Bosch Tronic 3000T ES8.

For the Ariston GL6+S electric mini-tank water heater we sell the replacement for the sacrificial Anode Rod (#87387044480) (Old number #570241). This slightly longer part can also be used for the Bosch Pro Ariston GL8Tiand ES8 mini-tank water heaters.

The new Ariston GL2.5S/GL4S take a new Wired Thermostat #87387044410.  The old part number was #7738002302.  This new wired thermostat can also be used for the GL2.5TiS/GL4TiS and the ES2.5/ES4.

The new Ariston GL6+S takes a new Wired Thermostat #87387044420. This new wired thermostat can also be used for the ES8.

Bosch Therm 520HN & 520PN Installed at Elevation

The Bosch Therm 520HN and the Bosch Therm 520PN can be installed at elevations for people with homes or cabins in Colorado, New Mexico, etc.  The Bosch 520HN & 520PN are natural drafting units and require a 6" galvanized type B-vent and must vent vertical for a minimum of 6' to the rain cap for all elevations over 2,000'.

Gas pressure is dependent upon the gas type whether it is Natural Gas (NG) or Liquid Propane (LPG) and also the length of the gas line.  See sizing charts in the installation manual for the heaters.  The Bosch 520HN & 520PN can be installed above 4,500' elevation but the unit would have to have the gas pressure adjusted using a manometer to compensate for the air and gas mix at the high elevation.  Please see the insert below for more details.

Cutting the gas pressure back as per the chart above is called "de-rating" the burner.  Elevations above 2,000 ft require the Bosch tankless water heater to be de-rated 4% for every 1,000 feet.  Basically you will loose 4% of your heating capacity for every 1,000 ft.

Bosch 5" B-Vent Vertical Vent Kit (H/P VVT)

The Bosch Vertical Vent Kit (H/P VVT) is a 5" Galvanized, Type B Vertical Vent Kit. This vertical vent kit includes a 5" x 12" pipe, (2) 5" flexible 90 degree elbows, a 5" fire stop support, a 5" roof flashing, a 5" storm collar, and a 5" rain cap. The HP VVT Vertical Vent Kit is manufactured by Selkirk and is used only for the Bosch Therm 520HN and 520PN naturally drafting heaters.  The H/P VVT vent kit will also work for the older retail models 1600H and 1600P.

The venting system must be designed and constructed so as to develop a positive flow adequate to remove flue gases to the outdoors.  Consult the National Fuel Gas Code if the vent will have elbows or share venting with another natural draft appliance.  The vent system must have at least a 12" rise off the top of the heater before any elbows or vent connectors.  

4" Z-Flex Stainless Steel Venting for Pool Heaters

Globaltowne carries a large supply of the 4" Z-Flex Stainless Steel (AL29-4C) venting and pool heater adapters.

The 4" stainless steel venting comes in all different lengths ranging from 6" - 5' long.  We carry all of the elbows, wall thimbles and terminators also.

Globaltowne carries all kinds of adapters for any type of pool heater and many different tankless water heaters.  The 4" Sta-Rite/Pentair Pool Heater Adaptor (4STPHA04) is the most common for the pool heaters and we always keep plenty on hand.

Mr. Heater Propane Indoor/Outdoor Heater/Cookers

Globaltowne is pleased to announce we are now carrying a full line of Mr. Heater Indoor/Outdoor Heaters and cookers.  The Mr. Heaters run on Liquid Propane (LPG) gas and can either be hooked to a 20 lb LP tank or the small propane cylinders.  The Mr. Heaters are designed for heating different size areas depending on the BTU size of the heater.  There are also heater/cookers which are great for camping and the outdoors. Please see the full line of heater/cookers listed below.

The Mr. Heater MH18B Big Buddy Heater is a portable 4,000 to 18,000 Btu space heater that can heat a space of up to 400 sqft and can be used for both indoor and outdoor applications. The heater attaches to either a 20 lb propane cylinder with an optional hose connection or to two 1 lb disposable propane cylinders with a new swivel out regulator. This portable space heater also comes with an automatic safety shut off in case of accidental tip-over or low oxygen as well as a battery operated fan (batteries not included).

The Mr. Heater MH12B Hunting Buddy Heater is a portable 6,000 to 12,000 Btu space heater that can be used for outdoor recreational applications. The heater attaches to either a 20 lb propane cylinder with an optional hose and filter or a 1 lb disposable propane cylinder with a new swivel out regulator. The heater also comes with extra storage space that can house a spare 1 lb propane cylinder, gloves, or other accessories. This portable space heater has an automatic safety shut off in case of accidental tip-over or low oxygen.

The Mr. Heater MH9BX Buddy Heater is a portable 4,000 to 9,000 Btu space heater that can heat a space of up to 200 sqft and can be used for both indoor and outdoor applications. The heater attaches to a 20 lb propane cylinder with a new swivel out regulator and optional hose connection or directly to a 1 lb disposable propane cylinder. This lightweight and easy to carry portable space heater also comes with an automatic safety shut off in case of accidental tip-over or low oxygen.

The Mr. Heater MH4B Little Buddy Heater is a portable 3,800 Btu indoor space heater that can heat a space of up to 100 sqft. The heater attaches directly to the top of a 1 lb disposable propane cylinder. This lightweight portable space heater also comes with an automatic safety shut off in case of accidental tip-over as well as a low oxygen sensor.  The MH9BX Buddy Heater is perfect for every day home use, garages, workshops, and roadside emergencies.

The Mr. Heater MH15C Propane Heater is a tank top heater that attaches to the top of a 1 lb disposable propane cylinder and comes with a foundation base that allows you to alternate use between a space heater and cooking stove. The propane cylinder is not included. This outdoor only space heater is similar to the MH15 but can also be used as a cooking stove. The MH15C heater/cooker has an adjustable high to low heat control with a 10,000 to 15,000 btu range and an automatic safety shut off is also included.  This small, easy to pack, space heater is perfect for all outdoor recreational activties including camping, fishing, hiking, and tailgating.

The Mr. Heater MH15 Propane Heater is a tank top heater that attaches to the top of a 1 lb disposable propane cylinder and comes with a foundation base to insert the propane cylinder into. The propane cylinder is not included. This outdoor only space heater has an adjustable high to low heat control with a 10,000 to 15,000 btu range. An automatic safety shut off is also included.  This small, easy to pack, space heater is perfect for all outdoor recreational activties including camping, fishing, and hiking.  The Mr. Heater MH15 Outdoor Propane Heater is the direct replacement for the Paulin 5500 Heater.

Globaltowne Clearance Heaters

Globaltowne is always bringing in new and upgraded Bosch gas and electric tankless water heaters. Globaltowne currently has a few Bosch gas tankless water heaters on clearance.  These units are priced to sell to make room for new stock.  All of the Bosch tankless water heaters that Globaltowne sells are brand new and come with a full warranty.  There are many different BTU size units for all types of homes for both indoor and outdoor installations.  Please see the links below for the heaters on clearance.

Clearance Heaters
Bosch Integra 500 LP (Liquid Propane)
Bosch Evolution 500 NG (Natural Gas)
Bosch Evolution 500 LP (Liquid Propane)
Bosch Therm 660EFO NG (Natural Gas) Outdoor unit

Please visit our Globaltowne website at www.globaltowne.com for more information on the tankless water heaters and accessories.

Humphrey Preformed Mantle L13-2 for Model 9 Gas Lights

Humphrey Preformed Mantle L13-2 for Humphrey Gas Light Model 9 (1 mantle).  Cross reference part:  #8 Mantle.  The L13-2 is intended for use with Humphrey Burner Nose L12-2A.

The Humphrey Pre-formed Mantle L13-2 is intended for use with all model 9 Humphrey Indoor Gas Lights. Use in only stationary conditions such as buildings (not recommended for recreational vehicles).

The Humphrey Preformed Mantles also come as a 6 pack and the part number is L12-2-6pk (6 Mantles).

Determining Gallons Per Minute (GPM) of Water Flow from Household Fixtures

The flow rate of a faucet or shower head is measured in gallons per minute (GPM) and is a critical factor in sizing a Bosch tankless water heater, or for evaluating if an older fixture is wasting water.

The Federal Energy Policy Act of 1992 required all faucet and shower fixtures made the USA to have a flow rate of no more than 2.2 GPM at 60 PSI. Often you can get below 2.2 GPM with low flow aerators. However before 1992, older fixtures used much more water than 2.2 GPM, sometimes upward of 10 GPM. So before any calculations for water heater sizing can properly be done an accurate measurement of a fixture's flow rate should be done. If any fixture is much more than 2.2 GPM, it is a good candidate for replacement with a new code compliant water efficient fixture.

Here's how to quickly determine flow rate for a specific faucet or shower head:

Turn the fixture on to its normal position

Place a container under the fixture and collect the water for 10 seconds

Measure the quantity of water in the container and convert the measurement to gallons (e.g., 0.25 gallons)

Multiply the measured quantity of water by 6 to calculate the flow rate in gallons per minute (0.25 gal x 6 = 1.5 GPM).

For sizing of a tankless water heater you would want to determine the most applications (uses) at one time you would be using in the worst cases scenario.  As an example, You normally run 2 showers at the same time and the laundry going too.  Each shower flows 2.0 GPM and the Laundry flows 1.5 GPM so that would be a total of 5.5 gpm.  Using this calculation you can then find a unit that would give you at least 5.5 gpm with an output temperature of 116 degrees or better.  

You can call us at 888-726-9752 for help with sizing a Bosch tankless water heater.

Negative Air & Freeze Prevention for Bosch Tankless Water Heaters

Negative Air in the older Bosch naturally drafting units and the new Bosch tankless water heaters such as the Bosch Therm 520PN, 520HN and 330PN is something that needs to be considered when installing the tankless.

Negative air pressure in a structure occurs when air consumed by fuel burning appliances or exhaust systems in that structure exceeds the amount of air available.  Here is a list of items that consume air within a typical household:

• Stove exhaust fans
• Furnaces
• Water heaters
• Fireplaces/ Woodstoves are the worst as they consume a lot of combustion air
• Bath fans
• Dryers

All of these items must be taken into account when making provisions for a proper amount of fresh air from the outside.  If the building is new construction, air infiltration from the outside will be limited and provisions for extra air supply should be made. If the building is older construction, air may infiltrate into the house through unplanned sources such as window frames, door jams, sill plates or idle chimney flues. These sources still may not be providing the adequate amount of air and additional sources of fresh air should be considered.

Why Negative Air Is Bad

Cold air from the outside is drawn through the water heater’s flue pipe because other fuel burning appliances or exhaust systems in the structure require more air than the dwelling can supply. When the required amount of air for the fuel burning appliances or exhaust systems in the structure is not being supplied to them, they find the flue pipe on the water heater an acceptable means of supplying themselves. Thus, freezing cold air is pulled down the water heater’s flue, drawn over the copper heat exchanger, potentially freezing it and the water valve below. Because, when idle, the water heater holds only cold water, freezing can happen quickly possibly causing leaks or ruptures in the heat exchanger and/ or the water valve. The water heater does not pull air through its flue pipe – if you were to remove the heater, the air would continue to come down your flue pipe. You must have the air balanced in the structure to correct this problem. Consultation with a heating, ventilating and air conditioning (HVAC) specialist is recommended.]

There is also another alternative to combat negative air for the Bosch 1600P, 1600H, 520PN and 520HN naturally drafting heaters and that is to use the AQ4 powervent kit.  The AQ4 powervent kit is for venting the appliance out the sidewall of the building and comes with a termination hood with built in flapper to keep the cold air from coming in when the heater is not being used.  The AQ4 powervent kit requires power to operate the blower motor which blows the exhaust gases to the outside.  The AQ4 powervent kit is not approved for the older Bosch 1000P and the new Bosch Therm 330PN as the unit is not large enough to use the powervent motor.

All larger Bosch tankless water heaters that are direct vent units meaning they have a built in fan, are sealed combustion and have the ability to take the intake air from the outside should always use this method and take the combustion air from the outside in all cold climate areas.

Bosch Thermotechnology Production Milestone of 20 Million Water Heaters

Bosch Thermotechnology Production Milestone of 20 Million Water Heaters.

Bosch Termotecnologia S.A’s Aveiro plant, 70 kilometers south of Porto in the northwest region of the country, passed the 20 million mark in production of gas-fired water heaters this past fall. Vulcano brand gas water heaters are the market leader for tankless water heater technology and are sold throughout Europe and exported to North America where they are sold under the Bosch Greentherm brand name. In the U.S. Greentherm water heaters are ENERGY STAR rated products. 

GreenTherm tankless water heaters are wall-mounted gas condensing water heaters and ENERGY STAR rated with an energy factor of 0.95 with venting options to fit any installation requirement.

Bosch has been manufacturing in Portugal since 1911 and at the Aveiro facility since 1977. At Aveiro it currently employs about 1,000 associates in R&D and manufacture of water heater products for both residential and commercial applications. The company celebrated the milestone production achievement on October 29th with Bosch Thermotechnology Portuguese and German representatives on hand to mark the occasion. The international Bosch Group operates five facilities in Portugal for automotive, industrial, construction and household and business use technologies and employs over 3,000 people, making it one of the largest industrial employers in the country.

1.866.289.4652

Bosch Therm 330PN Replacing the Bosch Aquastar 38B

The Bosch Therm 330PN gas tankless water heater is a point-of-use water heater designed to provide instant hot water for two sinks. It can, in some locals be used to provide hot water for a single low flow shower.  

The Bosch 330PN is 75,000 BTU's and can deliver 2.6 GPM of hot water at a 45 degree F temperature rise. A regular shower head delivers about 2.0 - 2.5 GPM, so the Bosch 330PN is right on the edge for delivering water for a hot shower.

However, if you live in a warm climate, such as Texas, Southern California, Florida, Arizona, etc, then you probably do not need to raise the water temperature by 45 degrees, so the 330PN can work for a single shower.

Also, if you use a low-flow shower head that reduces your flow to say 1.5 GMP, then again you can have a hot shower with the Bosch 330PN.

We would not recommend the Bosch Therm 330PN for a regular flow shower head in New York -- it just will not be able to keep up and provide you with a hot shower due to the cold incoming water.  The Bosch Therm 330PN is not designed or approved for preheated inlet water..
The Bosch 330PN is a good replacement for the older Bosch Aquastar 38B. The 38B was 40,000 BTU's and only delivered about 1.3 GPM at the same 45 degree F temperature rise. So, the 330PN really is a much stronger water heater than the 38B ever was!

The Bosch Therm 330PN takes the same 4" venting as the 38B did and must be vented vertical up through the roof.  The 330PN CANNOT be powervented out the sidewall of the building.

The Bosch 330PN comes in both Natural Gas (NG) and Liquid Propane (LPG) models.

The Bosch 330PN is designed for heating potable water only and is not approved for space heating applications.

Humphrey Tie-On Burner Nose L12-11A Back in Stock!

For over a year the manufacturer has had the Humphrey Tie-On Burner Nose (L12-11A) on backorder.

As of today we again have this Humphrey / Paulin replacement part in stock!

Order online at www.globaltowne.com.

Procedure for Programming The Wireless Remote TSTAT2

The Bosch Wireless Remote Control (TSTAT2) is used to remotely control the temperature of the Bosch Therm tankless water heater. The TSTAT2 does NOT have the ability to remotely reset the Bosch Therm hot water heater. Below is a more in depth procedure for installing the remote control.

The Bosch Wireless Remote Control (TSTAT2) is designed to work with the following Bosch Therm Tankless Water Heaters: C 1210 ESC, C 1210 ES, C 920 ESC, C 920 ES, C 1050 ES, C 800 ES, Integra 500, C 950 ES, 940ES, 940ESO, 715 ES, Evolution 500 and 830ES as well as the Bosch AquaStar 2700ES and 2400ES heaters.

TSTAT2 Remote Control Installation:

On the "heater" control panel, press and hold Program key while
pressing the ON/OFF button to ON.  Release program key when LCD
displays “188”.  LCD shows “P2”. If not, repeat previous step.

1. Press the + button on the heater to select "P3".  Press and hold Program 
key again for 1 sec.  LCD shows one number and one rotating digit. If not, 
repeat previous step.

The number represents the remote control which is to be registered, the
first remote control will be registered with number “0”, the second with
number “1” and so on.  The rotating digit shows that the electronics is 
expecting a registration and waiting for response from wireless remote.  
If the LCD fails to show a number and rotating digit after repeated attempts, 
double check the wire connections made in section 5.1.

2.  Hold wireless remote control in front of the control panel on the heater and
simultaneously press remote control buttons until the temperature indication 
is shown on the remote control LCD.

3.   Press ON / OFF button on the front of the heater to OFF position and then
back ON.

4.  Press buttons + or - on the remote to reach desired temperature.

New remote control is programmed.

To program a 2nd or 3rd remote to the same heater, follow the steps above and 
then after the remote is programmed you will be able to use the first or 2nd or 
3rd remote to raise or lower the temperature on the heater.  Please remember
the remotes cannot be used to reset the heater if an error code should appear.