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Base board heating thermostat


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17 replies to this topic

#1 harringg

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Posted 05 February 2011 - 12:39 PM

We have an add-on room that is not part of the main central air system. There are two 220V (240V?) electric baseboard heaters. At the circuit box there is a regulator box (Type R841C10293, 240V 50-60 CY, Series 80 Thermostat Heater setting, 0.2 AMP). Those wires run to the wall thermostat in the room with the baseboards.

In the room with the baseboards, there is a digital thermostat on the wall with two small wires, white and red and there is 24V across those wires. Things don't seem 'right' in terms of regulating the room temp. I bought a Honeywell CT87K. Hooked up the R/W wires, set the system type DIP switches to 1/2 (Electric warm air, 9 CPH).

Does this seem correct? What I mean is, should the two heaters be controlled directly from a line voltage regulator/thermostat?

This is how the house was wired when we moved in.

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#2 harringg

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Posted 05 February 2011 - 01:28 PM

As a quick followup. The new CT87K is set to off (turned all the way to the left), the readback on the bottom dial is 68F, the desktop thermometer in the room is reading back 68F.

I'm guessing the issue is that this is the wrong type of thermostat, or the system is wired to on only or off only. I mention that because down by the circuit box, in addition to the breaker that shuts the power off, there is a three-way light switch in a box that is Heater-ON, OFF, Power to Central Air-ON

Any ideas to get this situation wired to make the baseboard heat more regulated?

#3 RegUS_PatOff

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Posted 05 February 2011 - 01:36 PM

I haven't done any research on that controller, yet,
but there would seem to be a 24v Relay (operated by the Thermostat) in the Control Box that controls the 220v to the BaseBoard Heaters.

Did it heat OK with the "old" Thermostat ?
Does it heat OK with the "new" Thermostat ?

R841C info

R841C more info


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#4 harringg

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Posted 05 February 2011 - 03:28 PM

When the cover is off the thermostat, and just the two wires are connected as shown, Red wire to R, White wire to W, there is still heat being produced from the baseboard heaters. It's staying ~68. There is no regulator in the baseboard heater.

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#5 RegUS_PatOff

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Posted 05 February 2011 - 03:32 PM

Yes, if there's (about 24v) across the Thermostat, it's OFF
The Relay Contacts in the Controller may be stuck ON.
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#6 harringg

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Posted 05 February 2011 - 03:42 PM

Ding, ding, ding.

It is possible this is what's happening? My gas forced air furnace thermostat which is reading back ~68F and it's in another part of the main floor of the house is regulating the baseboard heater? It's 68F in this room with the baseboard heater and the part of the thermostat that controls the temperature is removed (as shown in the picture above).

As mentioned earlier, there is a three way switch by the circuit box, so in the winter, it's switched to baseboard heat and causes the heaters to follow the readback from the main thermostat for heating, in the summer the switch is flipped to feed power to the outdoor AC compressor and cut any power to the heater, so it's not running at all, regardless of the readback at the main thermostat.

I've been in this house over 8 years now and never could figure the heat in this room out. :wallbash: I don't need a thermostat, just something to complete the loop it seems.

Logical conclusion, or is there something else to consider?

#7 RegUS_PatOff

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Posted 05 February 2011 - 03:52 PM

I don't know how it's all wired (with the 3-way switch)
but I would think the BaseBoard Heaters in the add-on room would be operated separately by their own Thermostat,
so then you could keep that room warmer or cooler, if needed, (at different times of the day) than the rest of the house.
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#8 harringg

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Posted 05 February 2011 - 08:34 PM

I was typing my last reply when you posted about the relay contacts being possibly stuck ON.

Now the more I think about it, the R/W lines as shown with thermostat cover off, are not physically in contact without the thermostat cover on. Therefore, even though the two wires have ~24V across them when measured with the multimeter, they are in fact not a closed circuit as pictured above.

I checked this by taking the base unit of the thermostat where the R/W attached, removing all wires (so it was as if it came out the package) and there is no continuity across the two posts R and W connect to. The closed system can not occur until the thermostat cover is in place.

As a side note, now the thermostat in the opposite end of the house is 70 and the desk thermometer in the room with the baseboard heat is reading back 70, and the baseboard is warm. Either it's coincidence, or the two systems are tied together. I'll need to keep digging.

Edit: I just set the breaker to OFF and measured the voltage across the bare R/W wires. 0V I then checked continuity across them and there is continuity while the wires are separated in space.

Edited by harringg, 05 February 2011 - 08:55 PM.


#9 jb8103

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Posted 05 February 2011 - 10:48 PM

I was typing my last reply when you posted about the relay contacts being possibly stuck ON.

Now the more I think about it, the R/W lines as shown with thermostat cover off, are not physically in contact without the thermostat cover on. Therefore, even though the two wires have ~24V across them when measured with the multimeter, they are in fact not a closed circuit as pictured above.

I checked this by taking the base unit of the thermostat where the R/W attached, removing all wires (so it was as if it came out the package) and there is no continuity across the two posts R and W connect to. The closed system can not occur until the thermostat cover is in place.

As a side note, now the thermostat in the opposite end of the house is 70 and the desk thermometer in the room with the baseboard heat is reading back 70, and the baseboard is warm. Either it's coincidence, or the two systems are tied together. I'll need to keep digging.

Edit: I just set the breaker to OFF and measured the voltage across the bare R/W wires. 0V I then checked continuity across them and there is continuity while the wires are separated in space.


There would be continuity. The thermostat is just a switch, effectively connecting R to W, closing the circuit. 24VAC can then flow from the transformer in the R841, through the thermostat, back to the resistance heater in the R841, heating up a snap disk which forces a microswitch to close, which closes yet another circuit, specifically the L2 in the 220VAC circuit. 220VAC then flows to the element in the baseboard unit producing heat. The R841 functions to connect or disconnect the L2 wire, opening or closing the 220VAC, turning off the heat when open and turning on the heat when closed.

When the cover of the thermostat is removed, the thermostat switch is removed with it, so the circuit is open. You could force a call for heat by simply twisting the R and W leads together, accomplishing the same thing the thermostat switch does, and the baseboard heater would continue to heat forever (actually until a high limit switch elsewhere in the circuit trips open).

You observed that the baseboard produces heat when the thermostat cover is removed and the 24VAC circuit is therefore open, i.e., disconnected.

But there are two loads here - two baseboard heaters. Are both baseboards producing heat when the CT87 is disconnected as above? Is the CT87 controlling both loads? If so there should be two R841 devices, one for each baseboard, both wired in series to the single CT87, at least according to Honeywell recommendations.

If the CT87 is disconnected and one baseboard is producing heat, there is likely a fault in the R841 controlling that baseboard. It should get pretty warm in that room.

RegUS_PatOff has much more experience than I do, and we should wait for his reply, or the other experienced techs here, but that's the way I see the situation so far, while there are several more variables to consider.

Edited by jb8103, 06 February 2011 - 01:53 AM.

First, do no harm.

#10 harringg

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Posted 05 February 2011 - 11:39 PM

Here's the latest. There are two baseboard heaters in the room. I turned the power switch on the silver box marked Elec Heat to the middle position (OFF) and let it sit for ~45 minutes. The forced air thermostat (main) was reading back 70, the room with the baseboard heat (which is now OFF) cooled down to 68. My thought was the desktop thermometer was just reading the 'rest of the house'. I know that doesn't seem logical, but trying to rule out variables. So with no power, it's not keeping the room at the same temp as the rest of the house. Simply turning the power on and keeping the two wires exposed and separate from one another (BEING CAREFUL TO NOT GO NEAR THEM) and the room warmed to the same as the other thermostat.

At this point the CT87 isn't even part of the equation. See the bottom picture for the "Don't try this at home" :stupid: picture. Power is on at the switch in the basement, two wires which were connected to the CT87 are reading back ~21V, clearly not a closed circuit, AND the two baseboard units are heating up. :kopkrab:

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#11 jb8103

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Posted 06 February 2011 - 01:14 AM

The CT87 is wired to a transformer somewhere, or we wouldn't be seeing any voltage across R and W, and it is a faulty transformer to boot, because we should be seeing more like 26 or 28 VAC, not 21.

There is only one R841? Both baseboards are heating up but not keeping the room warm?
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#12 jb8103

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Posted 06 February 2011 - 01:18 AM

Remember there are two circuits, the control circuit through the CT87 at 24VAC (nominal), and the power circuit to the heating elements at 220VAC (nominal). The exposed thermostat leads aren't likely to bother you, they are only 24VAC. Exposed 220VAC leads, like you'd find inside the R841, can kill.
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#13 harringg

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Posted 06 February 2011 - 01:26 AM

The CT87 is wired to a transformer somewhere, or we wouldn't be seeing any voltage across R and W, and it is a faulty transformer to boot, because we should be seeing more like 26 or 28 VAC, not 21.

There is only one R841? Both baseboards are heating up but not keeping the room warm?


There is only one R841 next to the circuit box. If there's a second one, I haven't found it.

No, both baseboards do heat up (when the switch is set to Elec Heat in the basement) and keep the room the same actual temperature as the read-back value on the main thermostat that is connected to the forced air furnace. That's what confuses me. When powered off at the Elec Heat switch, both heaters are off.

#14 harringg

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Posted 06 February 2011 - 01:34 AM

Remember there are two circuits, the control circuit through the CT87 at 24VAC (nominal), and the power circuit to the heating elements at 220VAC (nominal). The exposed thermostat leads aren't likely to bother you, they are only 24VAC. Exposed 220VAC leads, like you'd find inside the R841, can kill.


That's my point. The CT87 is back in the packaging from the store, at this point there is no thermostat in the room with the baseboard heat. The R/W bare wires are exposed and not touching each other (for testing purposes) and the Elec Heat switch is ON and the room heats up and the room temp is the same as that of the thermostat connected to the forced air system. I've put wire-nuts on each individual wire and turned the power on and the room is heating up. No thermostat is connected in the room now, no wires are connected together, and the room is heating with the two baseboard units.

Is there a way to test the R841 with a multimeter? What would I look for in terms of ACV?

Edited by harringg, 06 February 2011 - 01:35 AM.


#15 jb8103

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Posted 06 February 2011 - 01:37 AM

RegUS suggested a fault in the R841 and I think he's right. Don't go in there, my friend, it is serious killer voltage. I think you should turn the power to the baseboards off, replace any covers you may have removed, and call a tech.
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#16 Sparky1

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Posted 06 February 2011 - 10:58 AM

Have to agree with Jb, 240 volts is nothing to be playing with unless you know what your doing. Trust me on this, I work with it everyday & have seen too many people pay heavily for their lack of knowledge, 1 simple mistake can put your lights out permanently.

Edited by Sparky1, 06 February 2011 - 11:00 AM.

Let us Fix it Properly.

#17 harringg

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Posted 06 February 2011 - 07:54 PM

Report this morning.

Forced air furnace thermostat set to 62 overnight, it's temp readback on display: 67
Room with baseboard heat: desktop thermometer is 61.5, baseboard heaters are cool to touch.

Set forced air thermostat to 68, furnace kicked in until it 68, shut off and now baseboard heaters are warming up.

#18 harringg

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Posted 06 February 2011 - 07:59 PM

Have to agree with Jb, 240 volts is nothing to be playing with unless you know what your doing. Trust me on this, I work with it everyday & have seen too many people pay heavily for their lack of knowledge, 1 simple mistake can put your lights out permanently.


As mentioned earlier, I know enough to be 'safely' dangerous. Appreciate the emphasis on leaving it alone if it gets to working with that voltage.

I'm not going to do it, but shutting it off at the Main (which will cut power to the entire house) will allow it to be worked on safely, correct?




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