Bosch Aquastar 250SX - SUX!!!

I've had the Bosch Aquastar 250SX tankless water heater for a little over 4 years now. And I have to say it's been nothing but a pain in the ass.

We built this house in 04 and our goal was to build a very green energy efficient house. Tankless hot water does make sense and when its working, it works well; producing endless 122 degree hot water.

The initial problems I had were a loud groaning when the 250SX fired up, intermittent cold water surges, random errors that shut the unit down.

There are several factors that might explain the miriad of problems I encountered.

• New Model - When I purchased the 250SX, it was a very new model, and it is obvious that Bosch was still in the process of working out the bugs. At one point they sent a revised controller that was supposed to work better and later they sent an attenuator that would solve the loud groaning sound it made when it started. In the end they ended up sending me an entire new unit.
• Self Install - Based on a friend that installed his Aquastar himself, I decided I'd save the money and do it myself - big mistake. The actual installation wasn't that hard, but as it turns out there are internal adjustments that in theory don't have to be made, but in my case were essential to get the unit operational. The adjustments required a manometer to monitor the incoming pressure and a CO2 analyzer to monitor exhaust.
• Liquid Propane - I'm using LP instead of natural gas - LP doesn't burn as hot. Again without the tools, there's no way to accurately adjust the incoming LP pressure.
• Well water, not city water - I'm also on a well system, so my pressure ranges from 40 - 60 psi. In addition, when my well pump would kick in, a slight lull in the pressure caused the 250SX to shut down. So imagine you are in the shower, the pressure in the tank hits 40, the pump kicks in, Bosch shuts down, it then takes another 30 seconds for the Bosch to produce hot water. Meanwhile you are receiving cold water in the shower - not fun. This was eventually fixed when after two plumbers could not properly adjust the pressure tank, I called the drillers that drilled my well. For $100 they were able to adjust the tank in about a minute.

It took over a year to get the unit working trouble free and by that time I'd spent another $600 in technician and plumber charges. Bosch did reimburse me for $300 or so. Once I was up and running the unit has worked fine. That said there are a few things to remember when you use a tankless hot water heater.

1. From the time you turn the hot water on, it will take the Bosch at least 30-40 seconds to actually produce hot water. Add to that the time it takes for the hot water to travel through your pipes to the tap. And if you shut the water off for just a second and turn it back on, it's got to go through the entire startup cycle again, meaning another 30 seconds of cold water out the hot water tap. So you can't wash the dishes and turn the hot water on and off and expect to have constant hot water. This is more annoying than you might think. The end result is you do waste quite a bit of water, so if you live in a dry place and water is not plentiful, a tankless water heater might not be for you.
2. Minimum water flow - if you turn a tap on but just want a small amount of hot water, it may not be enough flow to fire up the 250SX and you'll just get cold water.
3. A tankless hot water heater is more complex than a standard hot water heater. Just the other day I got an EA error. I called Bosch and after 20 minutes of waiting for tech support, they had me disassemble the unit and clean the ignition contacts with steel wool. If this was my wife, that would have been another service call. For me it was a couple more hours of lost work. Most traditional tanks, you just ignore until 10 years later when they fail then you replace them.
4. The 250 SX is limited to 6.35 gallons per minute with a 45 degree rise. In other words 2 major appliances can run at one time, max. And if your incoming water is really cold, this can be optimistic.

Bosch technical support has been good (once I get them on the phone), but I'm not impressed with the overall operation and design of this unit. I'd consider Rinnai, they seem to have a better reputation.

Bottom line, tankless is cool, it takes up less space and uses less energy and you never run out of hot water, but you will use more water and they are more complex than a traditional hot water heater. My recommendation is if you buy one, make sure you buy it from someone local that will install it and be there to fix any problems that might arise.