We are considering putting in new radiant heat and replacing our old boiler with a Takagi tankless heater, as recommended by our radiant heat guy (who we like and trust).
We've gotten another opinion, however, that these tankless heaters are subject to liming up at the heat exchanger.
Does anyone know if this accurate? I question it. I've lived in south Germany, where the water has some much lime in it that it is almost undrinkable and clogs up coffee pots in a week, but everyone uses tankless flash heaters.
I have the Takagi tankless heater in my home. It was installed about two years ago. I have had no problems with the system what so ever. It does a good job heating the water for the radiant floor heat.
If you are using the tankless unit as a boiler for radiant heat then you are using it in a system where you are recirculating the same water over and over again. All the minerals and oxygen should react and become stable in a very short period of time (probably in a few days). After that no further reactions should occur unless you have a leak and your fill valve adds fresh water to the system. So liming should not be a problem in that application.
If you are using it for heating your domestic (potable) hot water, then you are always feeding it new water with more minerals and dissolved gasses. And in this case you might have trouble with liming (depending on your water, the heater's internal construction, etc.).
Thanks a bunch; that makes sense.