Bosch 125BO NG AquaStar Outdoor Natural Gas Tankless Water Heater

I bought and installed this unit for a 600sf garage-apartment conversion. The tankless concept appealed to me, because it makes no sense to waste energy keeping a tank of water hot 24/7. It also mounts on the wall outside- saving some precious indoor space.The heater was professionally installed, inspected, etc. and actually does heat water (thus the 2 stars). Unfortunately, that's the last positive thing I have to say about this $1,000 adventure.The heater is designed to switch on at a certain flow rate. Only 2 of my 4 hot water outlets are big enough to trip the switch- my bathroom faucet (brand new & in perfect working order) doesn't 'trip' the heater even when it's open all the way, and my washing machine (also brand new) never demands enough water to turn the heater on. This is NOT adjustable- there is no way to get the heater to turn on at a lower flow rate.It is also impossible to make 'warm' water anywhere in the apartment. The heater ONLY heats when the kitchen or shower faucet is open all the way- start mixing hot & cold, and the heater kicks off. This results in unexpected, instant cold shower!My solution? I open another tap wide open so i can wash my clothes in hot water or take a warm shower instead of a scalding/freezing one. When i do this, everything works as expected. I get whatever temperature water I want, and as much as I want, and of course the hot water never runs out. But this "solution" means I WASTE more hot water (and energy) than I actually USE! After paying $1000 to buy and install an energy-SAVING water heater, this is an infuriating end result. I could have used a traditional storage heater for about a third as much, and it would have worked exactly as expected.After asking around, I found out this is a common problem with tankless heaters. I wish I had done more homework before I made the purchase.

Pilot light was frequently going out. It would re-lite but not stay lit after releasing the button. Determined that the connections were not making good contact. Added a small bit of dielectric grease to each of the contacts in the thermocouple wiring harness, including the sensors on the pipes. This insures that corrosion is not a factor in keeping the tiny current flowing from thermocouple to pilot switch. After application, the pilot has not stopped in 4 years.

We've been using this water heater for 6 years, and overall it performs very well. Putting this outside made room inside in the old water heater closet, where we then installed a stackable washer/dryer. It was a huge improvement to our house.It provides plenty of hot water for our small 2 bedroom house, acting as the only water heater we have. The only complaint I have is that the pilot light does occasionally go out. We live on the coast near San Francisco, and I think the fog takes its toll on the thermocouple. Every 6 months or so I have to relight the pilot, and sometimes it just won't stay lit unless I take out the thermocouple and clean it with some emery paper. I'm finally replacing the thermocouple this week. It's a $10 part and if you are someone mechanically inclined a simple job to do.Overall I've been pretty pleased with it and would buy another one.

I'm a professional plumber/ licensed plumbing contractor in CA with decades of experience both installing and servicing tankless water heaters. I like the idea that Bosch brought their small work horse out in an exterior model but sealing the bottom and drawing in combustion air from the top has left several of these, one of which I just finished servicing after one month in operation with streaks on the glass view window and exterior. These have developed black streaks most likely from drawing in vented combustion gases into the combustion chamber resulting in excess condensate. In two cases both piezio igniters had failed and had to be replaced. In both cases, the home owners could not get through to Bosch and opted to purchase what should have been warranted parts through a third party. Like many accelerated generations of Bosch models, this rush to market without the brutal test of real time application leaves a lot to be desired. A nice touch with the new anti freeze ceramic heaters but if the power goes out during a freeze, good by Bosch. This is only for a home in a mild climate, not snow country. Bosch was originally a French company and if you love working on French cars, you'll love the same design philosophy that has remained, quirky at best. In their defense, I have seen Bosch 125 B models lasting over 2 decades without a single service call and absolutely no other tankless on the market can state that. If your are going to spend $1K on a tankless, a little due diligence is in order.

All tankless heaters conform to 1960's western European technology and back then we all used a small tankless at the point of demand. One in the kitchen for the sink and the laundry machine (not many people have a separate laundry room. another in the family bathroom. As houses and demand grew the 1970's oil shock hit and effected gas prices too. European Govt.s brought out strict energy regs and people began to switch to highly efficient central instant boilers assisted by highly insulated small tanks. These systems also heat the house in winter. An average installation costs $7,000 US dollars per 1000 sqft of house.These Bosch heaters are 50 year old technology built bigger for the USA to replace your usual central tank boiler.If you're going to use them I recommend using two smaller heaters (but that requires a plumber moving pipes around) one for kitchen laundry one for showers.BUT you're still using old tech. I now live in Mexico and here Bosch has local competition and the boilers cost half of these Amazon prices and have a 9 volt battery rather than gas pilot or 110v connection. Actually in Europe tankless heaters were used because most houses just had a cold water supply round the house and these heaters ran off a branch from the cold loop. You could try that .. just a couple of feet of copper pipe,,,, er bet it's not up to code though. When I look at the building services tech used in the USA I can't help notice the similarity to your car industry. Sorry.