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I recently bought a home with an oil fired Biasi furnace that has a Hydrostat 3250-Plus attached. It uses an old analog round dial thermostat, and I'd like to replace it with a new digital (wifi) thermostat. The old thermostat only has two wires running to it (T and T), but the new one I bought requires a C wire. I went down to the furnace to see if there was an available terminal only to discover the Hydrostat. The directions for the hydrostat show the two 'T' connections, but not a 'C'. It has a C1 and C2, but the manual says these are for a circulator. I'm not great when it comes to wiring diagrams, and I'm at wits end trying to figure out where to go from here. I've included links to the manuals I've been able to find. If I can't connect the Honeywell wifi thermostat, any ideas for other options?

I believe its page 23 on the first one, as we have the Riello option.

B10 SERIES BOILER manual

Hydrostat 3250 manual

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2 Answers 2

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It looks like you're out of luck. It appears that the transformer is inside the hydrostat, and it doesn't expose a C terminal. You could contact the manufacturer, and ask them if there's a workaround. Based on the documentation, there's no obvious way to connect a WiFi thermostat to the system.

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  • It ought to be possible to hook up a small power supply at the thermostat, though making that installation "elegant" could be a challenge... I would hope that the manufacturers of these thermostats have a standard kit (or at least standard advice) for that purpose, or that someone has come out with a second-source kit by now.
    – keshlam
    Commented Nov 16, 2014 at 16:14
  • @keshlam The thermostat manufacturer will tell you to upgrade your system. Now that C wires are required by more and more thermostats, systems are including the terminal more often.
    – Tester101
    Commented Nov 16, 2014 at 19:56
  • If you say so. I'd think they'd want to sell to anyone they could, whether a modern system or no, but if they'd prefer to reject customers it's their call...
    – keshlam
    Commented Nov 16, 2014 at 23:12
  • @keshlam They make battery powered thermostats as well, so they shouldn't lose a customer over it.
    – Tester101
    Commented Nov 16, 2014 at 23:31
  • Looking at the last line of your answer, I presumed that they do not make battery powered WiFi thermostats. If they do, you should clarify. If they don't (for power consumption reasons, perhaps), I stand my my statement that offering a locally-powered option would be an obvious way to sell WiFi thermostats to more customers.
    – keshlam
    Commented Nov 16, 2014 at 23:37
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You can have a look at this forum below, which talks about using an external transformer plus a PAM-1 relay from a HydroStat 3150, which must be similar to your 3250. http://www.thermostatforums.com/showthread.php?791-newbie-with-nest-gen-2

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    Commented Sep 29, 2018 at 22:43
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