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Hydrostat 3250+ adapting to new boiler?

ineffable Member Posts: 7
I moved my Hydrostat 3250+ from a Weil McLain WTGO-3 to a Buderus g115 ws3. The Buderus has half the BTU and half the mass of the old one.

The Hydrostat will run the burner to the set max temp of 180 degrees. After the burner turns off, the boiler continues to warm -- today it got to at least 221. The Hydrostat appears to be running the burner longer than is needed, and I am wondering if it is using the target temperature or 'curves' it determined for the old boiler. Question: Is this a thing? How quickly do old data points get wiped from the Hydrostat's memory so it can learn and adjust for a new boiler? Does it not learn if the only calls come from ZC/ZR and not TT (because in the summer the only call is from the indirect tank)?

The Hydrostat's thermal pre-purge function is turned on, so it should only fire the burner when the latent heat available is insufficient to meet the demand. On the WM, the Hydrostat would show "Pur" on its display; on Buderus it never does (even though it appears to be in that mode, as the circulator is running but the burner is off).

Hydrostat settings: factory reset yes, then low temp off (cold start), hi temp 180, efficiency 4, pre-purge on, circulator on TT and ZC/ZR, circulator hold off active. Hot water and heat work; the system has been checked by a Buderus installer/servicer and is running properly.



  • STEVEusaPA
    STEVEusaPA Member Posts: 6,127
    Are you sure the sensor is in the well correctly? Are you using the well specific to the hydrostat?
    HVACNUT Member Posts: 5,023
    Where is the water heater tied in? The Hydrostat (zone valves?) or a circulator zone board? If it's in the zone board, is there a wire from ZR on the Hydrostat wired in parallel to the hot for the indirect circulator? Switch on the Hydrostat on I, switch on the zone board is on priority. Like @STEVEusaPA said, check the probe and well. I know there's specific well insertion depth on some Buderus models so maybe the sensor isn't reaching.
  • ineffable
    ineffable Member Posts: 7
    The was all the way down in the well, but I reseated it. The well is an Electro-well EW-206 (Hydrostat specific but Buderus length).

    The indirect zone valve end switch is connected to the Hydrostat ZC/ZR, with the Hydrostat set to indirect mode. For all other zones, the thermostats are connected to a Tekmar zone panel, which connects to the Hydrostat T/T. The burner/damper and circulator are on the Hydrostat's B1/B2 and C1/C2 respectively. The indirect bypasses the zone panel as it is not a Tekmar TN thermostat, the panel does not support DHW priority, and there are no zones left).

    The Hydrostat reports a target temperature of 145 degrees, yet it still runs the burner to the high limit of 180 (and then presumably through thermal stacking the temperature rises even further); the disappearance of "Pur" (pre-purge) is also strange.

    HVACNUT Member Posts: 5,023
    The wiring is not correct. Page 5, diagram 6.
    Even the end switch for the indirect's zone valve will go to TT on the Hydrostat. When the aquastat for the indirect calls, it powers its zone valve AND the 24v coil to a DPDT relay (by others. But not by you apparently) that will close ZR, ZC, and EXTERNALLY power the circulator. That will bypass economy settings or thermal targeting.
    Bring a 2 wire low volt from the indirect zone valve to the Hydrostat. Mount a RIB2401D to the Hydrostat and make all your connections right there.