2 wire wiring a Honeywell RTH6590WF; not so simple it seems :)


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Old 02-14-16, 04:55 AM
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2 wire wiring a Honeywell RTH6590WF; not so simple it seems :)

Hi folks
I have 10yo Hunter programmable thermostats (that also runs on two AA batteries) Im trying to replace with Honeywell RTH6580WF Wi FI versions.

Ive got Oil fired furnace, two wire set up. One issue I have is out of the voltage transformer, valves bodies and furnace controls...... the wires have been hacked, spliced so at the thermostat I have telephone wire with two pairs twisted together to form the two required wires. (bought it that way!

Anyway
On the Hunters one wire goes to "W/B" and one wire goes to "RH" which is spliced to "RC" The Hunter manual says "RH" is 24v and "heat relay or valve" goes to "W/B". This has been working fine for years

SO
After reading the Hwell manual, setting the parameters for my system, I wire what was on RH to C on and what was on WB to RH on the new thermostat. Power on, Wifi connected, Here it click when I set the temp but its not triggering the furnace. Reversing the wires produces the exact same result.

I am reading 27v+ with a meter out of the voltage transformer. I read somewhere here that that may be an issue.



any advice is surely appreciated. I think Hwell support is open today; i can try that later too.

thx in advance
andrew
 

Last edited by andrewbny; 02-14-16 at 05:20 AM.
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Old 02-14-16, 05:26 AM
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What voltage do you read between RH @ C at the tstat? There should be a factory installed jumper between RC-RH
 
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Old 02-14-16, 06:59 AM
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Hi

At the transformer its actually 28vac

I have the Hunter connected the moment.
At the thermostat across "W/B" and "RH" is 29vac and yep the jumper is in place on the old one and the new hwell model

I measured at the back-plate without the thermostat snapped in place if that matters.

Wow its -1f out there today
thx
 
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Old 02-14-16, 08:36 AM
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Welcome to the forums.

It was -2 here in north Jersey this morning.

You need three wires from your stat to your boiler. Old phone wire is not an acceptable type of cable for that application.
 
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Old 02-15-16, 05:01 AM
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Thanks
Despite having Saturday and Sunday hours listed, I could never get HWell support on the phone. I've returned both units. What a shame

Thx for help folks
Andrew
 
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Old 02-15-16, 10:21 AM
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Honeywell support is not terribly helpful for slightly out-of-the-ordinary installations.

You should look to changing the wiring to multi conductor thermostat cable for future expansion.
Six conductor would be a minimum size that I'd run.
 
 

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