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Bosch Greenstar Boiler with FW200 control and indirect hot water tank

Hi I have a Bosch Greenstar Floor Boiler with the FW200 control and I have a indirect hot water tank on the side where I get my DHW. I’m have the hot water set at 128 F and the tank sensor says it’s either that or 130. Im having an issue when you take a shower, it lets the tank temperature drop from 128 to 83 before the boiler finally kicks on and heats the water so it gets cold in the shower. Then when it finally kicks on it takes a while but it only heats the water to 111 F. I checked in the installer settings and regular settings to see if there was any tank range controls and I couldn’t find any. I was wondering what I should do?


  • Ironman
    Ironman Member Posts: 7,221
    What make and model of indirect tank?
    It sounds like the sensor is defective or improperly installed.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • bufordtputts
    bufordtputts Member Posts: 4
    It’s a Buderus S32/5W
  • fenkel
    fenkel Member Posts: 162
    the floor standing boiler should have an temp sensor with it? didn't it?
    I used it on my system, but when I installed it ,I used thermopaste ( Honeywell ) on temp probe and also put more in the tank sensor/ aquastat hole. I fabricated a rubber stopper to hold the sensor in place.. (see pictures)

    No problems..
    also check to make sure that your indirect tank is considered a zone.. This will run the water heater like a heat zone, but all zones will use the same temp to heat the water tank..
    ( you didn't say what temp you running for heat zones??
    180. or different?)
    question... are you using a zone controller for zones?
    like a TACO, if so make sure that IDW is set to priority..

    I'm running a greenstar floor 131 boiler and also have the SST 80, gives me a huge amount for hot water...
    use system in a duplex...

  • fenkel
    fenkel Member Posts: 162
    more pictures