Home automation Technology Zero Carbon

Smart Thermostat Upgrade

The killer feature of a thermostat is that it automatically controls heating and cooling. A smart thermostat uses modern control techniques. An even smarter one integrates with the utility’s demand response system.

For many years, a Nest Learning Thermostat has controlled heating and cooling at Dismal Manor. About a year ago, I replaced the Nest Beta program edition with a current production Nest Learning Thermostat. In mid-April, we had a surprise run of hot days so I decided to change from heat mode to cool/heat mode. I made the change, found the thermostat calling for cooling, and hot air coming from the registers. What’s up, Nest!


  1. 2022-04-21 Original


  1. Google O/B Wire description
  2. Google HVAC behavior monitoring
  3. Ecobee Thermostat Product Page
  4. Open ADR automated demand response
  5. Virginia Corporation Commission
  6. Ecobee 3 User Guide
  7. Ecobee 3 OpenADR 2.0b Certified

Before Calling for Service

When installing the dual fuel beta unit, I miss-configured the O/B wire. Remembering that goof, I inverted O/B wire configuration and the unit continued to heat. I restored the normal O/B configuration. So, busted SSR or busted firmware. The first is easy, replace the device. The active base plate and removable unit must be matching components.

The Service Call

Dismal Manor contracts with Simmons Heating and Cooling to maintain the HVAC equipment. Each year, Simmons replaces filters, cleans heat exchangers, and tests the equipment. This service occurred in October, start of our fall shoulder season. At that time both heating and cooling were working satisfactorily.

I scheduled a Simmons technician to come out to troubleshoot the issue. The thermostat sets the O/B line to call for heat pump cooling and resets O/B to call for heat pump heating. A separate contact controls furnace firing. Either the heat pump or the furnace but never both is run when there is a heating demand.

The Simmons tech verified the symptoms. Then we did the following things.

  • Check reversing valve function at the compressor unit. The reversing valve was alive and well.
  • Check the wiring between the indoor and outdoor units. It was good. Recent work by other trades under the house had not damaged the HVAC control wiring.
  • Check the wiring between the indoor unit and the thermostat. It was good and each wire was connected to the proper thermostat terminal.
  • At this point, we confirmed that simulating the proper contact states at the thermostat wiring would cause the machine to cool.
  • Hypothesis: Either the Nest Learning Thermostat experienced a solid state relay (SSR) failure or a firmware failure was causing the O/B line to remain in the reset state.
  • The Nest Learning Thermostat could detect the presence or absence of the O/B line so I believe O/B SSR is working correctly and that the November firmware update is at fault.

Nest Thermostat Trade Reputation

Simmons technicians have never looked kindly on the Nest Learning Thermostat. The primary reason is that Nest engineers seem unable to use industry standard terminology to describe the thermostat terminals, connection schemes, and tuning parameters.

In the suspect November update, Nest had overwritten my heat pump lockout setting (something they had done with the Beta device that I reported). This was the second strike on this particular offense.

Nest had also changed the UI and configuration terminology including the description of the O/B contact. We suspect that a general practitioner lacking HVAC domain knowledge ran amok.

What to do

As an early beta-test dual fuel Nest Learning Thermostat site, I was able to use the beta-test ticketing system at Centercode and Nest was providing telephone support for installation issues as the instructions needed debugging. I won’t say that I was spoiled. I probably was. But Sergi and Larry are no longer active and management “optimizations” are happening.

Over the last 3 years, there has been a conspicuous reduction of engineering attention to the Nest Thermostat products and the Nest Protect products in the beta program. Alphabet has discontinued use of Centercode. My beta agreement requires that I return decommissioned equipment to Nest. They no longer (2021) want to be bothered. When I requested an RMA for the original beta thermostat through the ticketing system that replaced Centercode, there was no response. I turned the device in for E-waste recycling.

Alphabet has reorganized the division a couple of times. It is now extremely difficult to get through the maze of help pages and chat bots to talk to an actual human. The help pages actually help and are pretty easy to locate with a search. And they are well written.

But some issues, particularly novel ones not already documented, require support engineering attention. As of 21 April, I can find no mention of stuck O/B output in either the support or community pages.

At this point, it is unclear if the hardware is busted or the firmware is busted but cooling is out of commission. Fortunately, I found this in the spring while humidity is low. In August and September, loss of cooling can be life-threatening for seniors.

I’m unwilling to throw good money after bad to confirm that Nest has botched the November firmware update. I’m also unwilling to pick my way through the Nest maze in hopes that they’ll fix this issue before it gets hot in June. So I fired my 11 month old Nest Learning Thermostat.

Ecobee 3 Lite

Ecobee has 2 active thermostat products, the Apple HomeKit capable Ecobee 3 Lite and the Alexa-Embedded Ecobee Smart Thermostat. The first product is just a thermostat. The second has Alexa and Siri support built in. Both Ecobee Thermostats can also be the central communicating component of a home security system that includes door/window sensors and cameras from Ecobee.

Installation of the Ecobee 3 Lite is very similar to the installation of the Nest Thermostat. Mount the base, connect the field wiring to the base following industry conventions and standards, and fit the thermostat to the base.

To start configuration, you add the Ecobee App to your Android or Apple phone. The iPhone app handles WiFi network setup mechanics.

Once on the base, the thermostat wakes, configures WiFi, updates firmware if needed, and guides you through HVAC system configuration. The thermostat I/O detected the connected pins and asked about the configuration of the O/B contact in plan language. Specifically, it asked if the pin should be energized to cool. Simple and direct and understandable by field service folks. The setup dialog also asked if the heat pump and aux heat should be run together (common for electric supplemental heat but never for furnace supplemental heat.) The setup program also directed me to move the solo W2 wire to W/W1.

Dominion Automatic Demand Response

Dominion is in the process of implementing the OpenADR 2 automated demand response specification. This interface specification describes the interface between customer equipment and the utility’s demand response management system, commonly provided by a contractor that manages customer registration and operational communications.

Ecobee has completed its implementation [7] of OpenADR 2 calling the feature ECO+. OpenADR allows the utility to adjust the HVAC set point of each participating system to reduce demand during periods of high usage.

The more sophisticated demand response systems preheat or pre-cool the building before the setback period. If done well, summer humidity remains in limits while the building drifts up during the afternoon rush hour. Dominion uses a 3 hour rush hour period, 3 PM to 6 PM in the summer (May to September) and 5 PM to 8 PM in the winter (October to April). Both “seasons” have a base load rate from midnight to 5 AM and a day rate outside the afternoon rush hour.

Dominion currently does not offer automatic demand management in combination with the off-peak (time of use metering) plan. This is silly but is a matter of what it has asked the Virginia Corporation Commission to approve.

Setback Strategies

In the past, I have tried the Energy Star night time setback strategy with Honeywell thermostats. The end result is lots of blankets and lots of big dogs in bed with you. And cold feet. Although the thermostat was supposed to reach the day temperature by the set time, it never did so because it didn’t know the temperature difference between inside and outside.

Setting air conditioning back at night caused the machine not to run at all letting the building humidity rise to 70% or more RH. I’d awaken to a clammy building. And we were saving base load nuclear generation, not afternoon peaking unit generation. So now we focus our setback strategy on the afternoon peak.

Move to A Production Nest Learning Thermostat

In May 2021, I installed a production version of the Nest Learning Thermostat. My intent here was to participate in Dominion’s automated demand response program which they keep badgering me to do in their advertising. The Beta thermostat was not visible to Dominion’s contractor so not eligible to participate.

The Nest Thermostat is OpenADR 2 certified according to Energy Star. It was somewhat difficult to run down this information as there appears to be no definitive listing of OpenADR 2 certified products.

The irony is that Dominion introduced time of day rates in 2021. Customers moving from the Residential 1 rate to the Residential time of use rate are not eligible to participate in the ADR rate. I’d guess that a combination of rate approvals and COBOL hacking is needed to allow the two rates in combination.

Why Ecobee 3 Lite?

Church has a mess of them to coordinate multiple HVAC systems in a large converted office building. They just work. In larger spaces we use the remote sensors for occupancy sensing and to get a better sense of the space temperature. They just work. The building humidity is maintained, particularly in our hall and religious education spaces which are unused most of the week.

By davehamby

A modern Merlin, hell bent for glory, he shot the works and nothing worked.