[Hai-users] resetting tstat

[Brett Griffin]

I usually notice this during initial testing of a installed thermostat with
Gas Heat.  

Do you have a common running between the thermostat and the Furnace?  This
usually fixes this issue.  

The problem I see this with is as follows.  The Rc-80 calls for heat.  The
furnace fan turns on to evacuate any possible gas in the burn area.  This
last for about 30 seconds.  At the end of this 30 second evacuation period
is when the problem happens.  Gas furnaces start an ignition cycle to create
heat.  The furnace uses too much of the available power to the thermostat
for this process, and the RC-80 sees this as a power failure, and "resets".
This usually makes the thermostats turn off and then back on, but then
disable the thermostat from operating the furnace for safety reasons.

By adding the common wire, this usually allows enough current for the RC-80
to operate.  If not, a second option would be to add a 24vac power supply in
parallel to the red and common terminal of the thermostat.  However if you
use the second power supply option disconnect the common from the thermostat
to the furnace.  A even better route for this is the Thermostat isolation
board made by HAI.  It powers and isolates the thermostat electrically from
the furnace.

 Brett Griffin, Home Technology Consultant 
Architechtronics, Inc.
www.architechtronics.com
www.hometechdiy.com

-----Original Message-----
From: hai-users-bounces at tssi.com [mailto:hai-users-bounces at tssi.com] On
Behalf Of Joseph K. Vossen
Sent: Friday, November 18, 2005 4:57 AM
To: hai-users at tssi.com
Subject: [Hai-users] resetting tstat

Sometimes (maybe once or twice a year) some of my RC-80 tstats refuse to 
'call' for heat or cool despite the fact that the temp in the room is 
above/below the setpoint.  The only way to get it to 'call' is to remove and

then reapply power to the tstat.

While this is normally not a real problem, I am worried that this may happen

when we are out of town for a length of time and the heat does not come on.

Any collective words of wisdom?

thanks

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