Original message
| pdt1842
 |  "White-Rodgers 1F35-910 Replacement"
, posted Wed 6 Feb 09:54  
Trying to replace a White-Rodgers 1F35-910 thermostat and update with an electronic model. System is hydronic with zones; current wiring is a three-wire system, with R, Y and 4, connected to zone valves. One wire is the common, the other the call for heat (opens the valve) while the other calls for the valve to shut (call for cool?). Adding to this mess is the addition of a relay on two of the zones, which energizes separate wall-mounted fan units once the respective valve is open and de-energizes when the valve shuts.
WR only has two options - buy another 1F35-910, or upgrade to their $$$ electronic model. I don't want another bi-metal mercury model, and their electronic model seems to be overkill. Honeywell support recomments the RTH5100B, connecting the '4' wire from the WR thermostat to the W terminal. Supposing that works for the RTH5100B, is there any reason that it wouldn't work on any other thermostat with a 'W' terminal?
I'll add that these thermostats are used for heating only. AC was added to the house at a later date, and that system has it's own thermostat.
Any suggestions/recommendations would be appreciated! Thanks.
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| | pdt1842
| "Re(2):White-Rodgers 1F35-910 Replacement" , posted Mon 11 Feb 15:52
Thanks for your help. Was able to replace the WR thermostat with a Honeywell 87K, and they are calling for heat and opening/closing zone valves perfectly.
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