Nest thermostat losing power

[terhude]

Have had Nest Thermo for 4 years and worked fine.   Off most of summer, and when tried to use AC noticed it was dead.  Charged battery manually and reattached and heating and cooling systems both worked fine, but Nest lost charge over 4 hours and dead.

Charged manually again and works for 3 - 4 hours before battery dead.

Wired.  Y1 (cool).  G (fan).  Rc (power).    W1 (heat)  Rh. (power).       All dark except Rh grayed out.

    error message   e72 when all breakers turned off

    error message   n72 when all breakers turned on with Rh still grayed out?

Di I have a wiring issue even though all systems; cooling, fan, and hot water boiler work fine or is there an issue with the nest thermostat?         

[CoolingWizard]

@terhude The error code you are receiving is that you’re not receiving power from the system properly. What it is detecting is that there’s no power on the Rh wire.

if as you say you manually charge the Nest display and attach it and then the system works for about four hours then we know that there is indeed power on the Rh wire because that’s the power that is used to control your system using the thermostat. So this will indicate that there is a problem with your backplate. Try moving the wire in Rh to Rc. 
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AC Cooling Wizard

[terhude]

I have an Rc wire connected to the AC and the Rh is connected to the Heating boiler.

Do you recommend I switch the Rh and Rc wires around, or disconnect the cooling and put the Rh into the Rc only?  

[CoolingWizard]

@terhude No do not switch the Rc and Rh. When cooling is required it uses power from Rc to initiate Y and G. 

The next time you get an Rh N72 error, use a VOM and check for power.  The tricky part here is the thermostat can only choose a single Power Common and it uses Rc and C when Rh is present. 

AC Cooling Wizard