Hello All - I hope I can find an HVAC genius who can help!
I have in-floor heat, powered by a Weil-McClain boiler; controlled by a TACO SR506exp 6 zone panel
, running 6 TACO pumps. I also have AC connected to Air Handlers (3 of them - one each for Basement, Main Floor and Second Floor), each with supplemental heating radiators as a 2nd stage heating option, which respond to a call-for-heat in the event the 1st stage in-floor heat cannot satisfy the 'stat in the zone within 10 minutes.
At present, my home is equipped with 5 thermostats (all non-programmable) controlling 5 zones: Basement (AC/2 stage heat), Main Living Area (AC/2 stage heat), Upstairs (AC/2 stage heat), Garage (heat only), and Master Suite (heat only). 2 of the 'stats are heat-only Honeywell Rotary (old school); the other three are Aprilaire 8538s (1AC/2Heat).
Heat-only 'stats are used in the Garage (no AC), and the Main Suite (which allows fine-tuned zoned heat control for that area, while the Main Living Area 'stat controls AC for the entire floor, including the Master Suite.
Here's the problem: I wanted to replace every thermostat except the garage 'stat with a programmable model. I bought 4 of these to do the job
. I started with the heat-only analog rotary 'stat in the Master Suite. It had only two wires - red and white - and was essentially nothing more than a switch closing the circuit to TACO pump #3 via the SR506exp panel.
I attempted to wire the the red and white wires to "RH" and "W2" of the new programmable thermostat (wiring/connection diagrams found here on a nearly identical 'stat
). The red and white wire connects to the TT of zone 3 on the SR506exp
. It is my impression that each zone input on the SR506 has 24V passing through it - which is what the 'stat requires to function - and, sure enough, the 'stat immediately lit up and appeared to be functioning normally. After about 1 hour, I realized that the Master Suite was 78 degrees. The zone heating turned on - and remained on - constantly!
Something with this new 'stat will not allow the zone to remain off
when there is no call for heat, and starts to click quickly (and cause the red LED on the SR506 to flicker on and off in unison) when I increase the heat setting and cause
the 'stat to call for heat. Clearly, the stat isn't acting as a switch for the zone.
I thought that it was possible that the 'stat was robbing power from the zone, causing the malfunction, and then activated and connected a 24V (this is a 24VAC or
DC 'stat) common wire (there were two choices here, and I tried both: splicing from the commons from the other 'stats, and tapping the 24VAC common which was found on the SR506 - neither worked, though running a 24VAC Common wire from the SR506 to the 'stat did result in a brighter zone 3 LED on the SR506). The second I connected the power from the Red wire to the 'stat, and either the white or
the C wire, the 'stat lights up; the zone activates and will not shut down until I pull the wires off the 'stat.
1) What makes a 'stat incompatible with this sort of system?
2) Can I wire the 'stats to 24V SPTD relays
which then activate the zones on the SR506 (which is, itself, a relay box) - something, for instance, like this
3) Am I missing something? Why isn't this working right now?
Thanks very much for anyone who can help!