help with installing honeywell th8320wf on 2 wire hot water heating system

TinCanFury

Hello! I'm hoping this is the correct forum for this question...



I'm helping a friend to try and install one of these new honeywell th8320wf wifi thermostats to her condo's heating system. it's an old converted house in the Boston area that uses a hot water boiler with cast iron radiant units in the units.



Initially they asked their handyman to look at it, which he did, was unable to figure it out, and sort of left it at that, so he's given me some information but I have not had a chance to physically look at it personally.



The initial issue is that the current thermostat is a 2-wire model, and this new honeywell also requires a 24V common "c" wire. So I need to see if that wire was run at all, and if not, determine if running a new set of wires is feasible.



That said, he said that when he initially tried to install it that "the furnace would kick on, but not the circulator pump."



So, now, beyond the necessity of the "c" wire, I'm wondering if there may be something else at issue with their system or if this scenario is a common operating condition when a thermostat that requires the "c" wire is connected with just the R/Rh and W1 wires.



Any help with this is appreciated, and I'm sure I'm missing some useful bit of information, if so let me know and I'll provide it.



Thanks!

Jamie Hall

This might get more views

on the main wall -- but since Dan put it up on off the wall... that will help!



On a hot water system, the thermostat controls the circulating pump or zone valve, depending on the system.  An aquastat controls the boiler.



For that Honeywell, you will have to find a 24v constant on terminal on the system somewhere, and hook up the thermostat with all three wires.

DanHolohan

I moved it.

Good idea. Thanks, Jamie.