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Old 03-25-2010, 09:39 PM   #1
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Replacement Thermostat Problem!


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!

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Old 03-26-2010, 06:37 AM   #2
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Replacement Thermostat Problem!


Post the brand and model number of the thermostats you have.
Radiant In floor heating with a second stage aux heat. Should not have the second stage on a timer. Defeats the purpose of radiant in floor heat.

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Old 03-26-2010, 07:23 AM   #3
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Replacement Thermostat Problem!


Quote:
Originally Posted by beenthere View Post
Post the brand and model number of the thermostats you have.
Radiant In floor heating with a second stage aux heat. Should not have the second stage on a timer. Defeats the purpose of radiant in floor heat.
Hello beenthere:

The thermostats I'm using are in the first link in my post - they seem to be discontinued (Made by Totaline?).

I actually got this thermostat working - at least for the "heat only" zone in the Master Suite that I started with. It turns out that I confused the 24V tap at the side of the TACO SR506 control panel with the Common tap (there are two screwdowns right next to each other, and they read: "24VAC Com"). I thought that meant the same thing. Not so: one was hot, and one was Common; I had tapped into 24VAC hot for a common wire. Oops.

On the other comment: I'm not sure what you mean: if a zone isn't reaching set temperature within a prescribed time, a secondary stage kicks in (which is also radiant heat, but in the form of a radiator within the air handler which allows a fan to blow the air through its coils and sends heated air through the AC ducts to assist in raising the room temperature until the radiant heat catches up).

I thought I wanted that in concert with these new programmable thermostats to allow a faster heating response for cold mornings (because I'm programming this system to lower temperatures over night - but not more than 4 degrees from day temperatures, to prevent thermal mass recovery inefficiencies). This "second stage" has only kicked in during extremely cold mornings and days - and it also serves as a backup in the event I have a failure of zones (though I do have gas fireplaces as an alternate heating source if needed).
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Old 03-26-2010, 07:30 AM   #4
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Replacement Thermostat Problem!


The coil in your air handler is a convection device. Not radiant.

A radiant floor isn't suppose to be able to recover 4F in 10 minutes on a mild day.

A second stage forced hot air on a radiant floor system. Should be controlled by the thermostat. And bring the second stage on by temp drop only.

This will bring second stage on quicker in many instances. But, it also shuts it off much quicker. And allows the radiant to bring the temp up the last 1 or 2 degrees, depending on thermostat.

Bringing it in by a timer will hold it off longer. But uses the it to satisfy the heat call. Which often doesn't allow the radiant mass to get to full temp. And then on the next heat call. It still needs the second stage to heat with.

Allowing the stat to control it based off of room temp. Makes for a more comfortable house/room.
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Old 03-26-2010, 07:58 AM   #5
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Replacement Thermostat Problem!


Quote:
Originally Posted by beenthere View Post
The coil in your air handler is a convection device. Not radiant.

A radiant floor isn't suppose to be able to recover 4F in 10 minutes on a mild day.

A second stage forced hot air on a radiant floor system. Should be controlled by the thermostat. And bring the second stage on by temp drop only.

This will bring second stage on quicker in many instances. But, it also shuts it off much quicker. And allows the radiant to bring the temp up the last 1 or 2 degrees, depending on thermostat.

Bringing it in by a timer will hold it off longer. But uses the it to satisfy the heat call. Which often doesn't allow the radiant mass to get to full temp. And then on the next heat call. It still needs the second stage to heat with.

Allowing the stat to control it based off of room temp. Makes for a more comfortable house/room.
I may have misled: my thermostats do control the 2nd stage - and are set to add the convection heat if the system isn't responsive enough.
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Old 03-26-2010, 07:59 AM   #6
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Replacement Thermostat Problem!


But did you set them to do it by time, or by temp only?
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Old 03-26-2010, 08:11 AM   #7
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Replacement Thermostat Problem!


Quote:
Originally Posted by beenthere View Post
But did you set them to do it by time, or by temp only?
Temperature only. One of the reasons I got these particular thermostats is the complex programming capability: I want to be able to drop the temperature in the house 4 degrees at night, and also be able to use the 'stat's ability to kick in secondary heat only when the system has attained preset temperature but is unable to maintain it with 10 minute cycled operation.

I also wanted the vacation mode programming.
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Old 03-26-2010, 08:43 AM   #8
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Replacement Thermostat Problem!


Should have got a good Honeywell.
With Adaptive recovery. only bring in the aux if needed.

10 minute cycle operation is, 5 minutes on, 5 minutes off.

Or are you calling cycle, just the on time?
Radiant floor heat should be set to a CPH of 1 or 2.

2 tends to give a more consistent floor and room temp then 1. Plus nice long efficient boiler cycles.
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Old 03-26-2010, 09:17 AM   #9
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Replacement Thermostat Problem!


Quote:
Originally Posted by beenthere View Post
Should have got a good Honeywell.
With Adaptive recovery. only bring in the aux if needed.

10 minute cycle operation is, 5 minutes on, 5 minutes off.

Or are you calling cycle, just the on time?
Radiant floor heat should be set to a CPH of 1 or 2.

2 tends to give a more consistent floor and room temp then 1. Plus nice long efficient boiler cycles.
I can set the second stage for whatever I want - I believe this 'stat has all the features of Honeywell's VisionPro and above (Prestige?) series (though VisionPro has facilities for only one stage of AC and one of Heat).

I will set CPH to 2: right now it is set for 1. Thanks!

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