Programmable Thermostat - Boiler


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Old 01-17-07, 09:00 AM
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Programmable Thermostat - Boiler

Hi,

I've installed several programmable thermostats on furnaces without a problem but need to some advice on a boiler system which I have no experience with.

I have a relative who has an older home (~80 years old) with what I believe is a newer boiler (within the last 8 - 10 years). They purchased a Honeywell RTH230B programmable thermostat which I think is compatible with a boiler / steam system. I was at their house about a year ago so my memory isn't that great but it looked like they had a fairly old thermostat (round type) that they are currently using. There are 4 wires that look to be original to the house. I don't think they were different colors. Two of the wires aren't being used, they are bent back on themself and pressed against the back of the thermostat mounting plate. The other two wires are attached to the thermostat but there is no indication of Rh/Rc/W/Y/G.

I assume these two wires would be attached to either the Rh or W on the new Honeywell thermostat. If this is true is there any harm to the boiler to install one to the Rh and one to the W and see if the thermostat works? If there are reversed would the system not come on? I would think I would just reverse them?

Also, on Gas forced air furnaces I have always turned the power off at the furnace before installing the thermostat. Does the boiler need to be turned off (if so how do I do this) before installing? I know nothing about boilers so this is all very new to me.

Appreciate any help/advice,

Thanks,
Mike...
 
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Old 01-17-07, 09:28 AM
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My understanding is that it shouldn't matter on simple t-stats.

When the temperature is not satisfied, like a light switch, the connection between those 2 wires closes (connects the signal from those two wires) until it reaches the target temp and then the contacts open up.

The other wires may have been for A/C, 24V, venting who knows...
 
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Old 01-17-07, 09:33 AM
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Who is correct. The stat is just a switch but you may need to confirm which wire is the hot. The stat may reqhire it to be on the RH/R terminal in order to power the stat. You may also need a common wire.
 
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Old 01-17-07, 09:54 AM
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Originally Posted by mattison
Who is correct. The stat is just a switch but you may need to confirm which wire is the hot. The stat may reqhire it to be on the RH/R terminal in order to power the stat. You may also need a common wire.
Can I just connect one to RH and the other to W and see if it works? Is there any possiblity of harm to the boiler and/or wiring doing this? How can I determine which wire is hot? I'd like to help them install the thermostat but don't want to risk them being with out heat (it's actually starting to get cold here in Michigan).

Appreciate all the help!
Mike...
 
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Old 01-24-07, 04:51 AM
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Originally Posted by mwillard65
Can I just connect one to RH and the other to W and see if it works? Is there any possiblity of harm to the boiler and/or wiring doing this? How can I determine which wire is hot? I'd like to help them install the thermostat but don't want to risk them being with out heat (it's actually starting to get cold here in Michigan).

Appreciate all the help!
Mike...
Can someone advise me on the above.

Thanks,
Mike...
 
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Old 01-24-07, 05:46 PM
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Rh and Rc are included on tstats to seperate systems with different control circuits. Rh connects to W during a call for heat, while Rc connects to Y and G during a call for air conditioning. A jumper is placed between Rc and Rh in cases such as a furnace with an AC coil installed.

It sounds as if you are dealing with a basic 2 wire heat only system, whether with zone valves or single zone. Both operate the same, with Rh connecting to W during a call for heat, so connect you 2 wires to those terminals. It's always safer to turn your system off first, both as a good work habit as well as to protect you equipment.
 
 

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