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John, restaurant equipment technician
Category: Appliance
Satisfied Customers: 2121
Experience:  25+ years experience. I'm now employed by a commercial cooking equipment service company
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i have a bosch aquastar aq125-b tankless water heater using

Resolved Question:

i have a bosch aquastar aq125-b tankless water heater using propane. I'd like to convert it to nat gas. Is there a kit avail for this conversion?
Submitted: 5 years ago.
Category: Appliance
Expert:  John replied 5 years ago.

Try going to, and enter your model number. If a kit is available, they should be able to help you purchase one. If a kit is'nt available, you can drill the present burner orifice to twice the size of the hole you have now. You'll need to install a gas pressure regulator that's rated for natural gas use. It does'nt need to be a Bosch brand, just one the threads onto the gas supply pipe you use for the natural gas

supply pipe.

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Customer: replied 5 years ago.
when you say drill out orifice to double the size what do you mean??? double the diameter? double the open area? what size (number drill do I use). I had already tried bosch's website--no help. HouseNeeds has a number of parts that I might need: pilot injector, gas valve, regulator, etc. It seems too simplistic to just change out the regulator.
Expert:  John replied 5 years ago.
The orifice hole size needs to be twice that of the present hole size. The drill number needed depends on the drill size used originally. Once the orifice is drilled to the correct size and installed, you need to install the proper gas pressure regulator, and adjust the burner air shutter for a bright blue flame with minimum yellow tipping.
Customer: replied 5 years ago.
twice the size in area? or twice the hole diameter, there is a difference. ie: if the current hole is 1/16 inch do I drill it out to 2/16??
Expert:  John replied 5 years ago.
Yes, you drill it to 1/8 inch. To make this a bit clearer, go to for a sizing chart.
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