We are having trouble at a customers install need 1 or 2 wifi thermostats on the system. Ecobee has been in place for 2 years and causing problems with call for aux heat etc. Residence is in NE US. Installation - Premier IntelliZone 4 Zone Control - model ZCK4 (also VENMAR CONSTRUCTO , and waterfurnace NSH036 Single Speed 34,000 BTU horizontal unit with hot water desuperheater 1 – EAMH10 10kw auxiliary heater) Ecobee EB-STAT-01 on Zone 1 and a Water furnace tstat TP32U03 on Zone 2. Any advice on modern design wifi thermostats that work with intellizone (esp nest or ecobee) From Ecobee Thank you for your note. There are issues with the ecobee working with the Intellizone depending on the model of ecobee you are using with the intellizone and when it was manufactured. Smart SI manufactured after June 2013 should work with the intellizone. Smart thermostats and Smart SI thermostats manufactured before June 2013 may or may not work depending on the voltage of your system. If you have a smart SI, the best thing to do is to contact ecobee support with the serial number to find out the date of manufacture. If you have a Smart and it does not work with your Intellizone, you can return it to us. If you have a Smart SI that is manufactured before June 2013 we can replace it with a newer one. We believe this is caused by a design flaw in the Intellizone – I am sure they believe it is a flaw in our design – we know you just want a solution. Here is a more detailed description of the situation in case that is helpful. The Smart SI/EMS SI and Smart and EMS designs are based on Relay technologies. This means when the relay is not actuated we essentially have infinite impedance across the relay contacts. When the relay is actuated, the contacts are closed and we have zero impedance. And thus there is no other impedance state for just a relay. But in ecobee designs as well as other thermostat designs we have a Varistor across the relay contacts. This is used to reduce contact voltage arcing which causes relay contact burn. Thus the Varistor increases the life/reliability of the relay. Varistors can be thought of as a variable impedance depending on the voltage applied across it. The Varistor in a HVAC installation may leak a little current depending on the HVAC voltage of the system. As you approach 30VAC and above this leakage gets bigger. This is what intellizone controllers may be seeing and causing false activation. A while ago we noticed that HVAC systems had supply voltages of 27-29VAC instead of the 24VAC standard. So we changed the Varistor from a 30VAC part to a 40VAC part. This was only done on the Smart SI and EMS SI products. Therefore, we believe newer Smart SI and EMS SI should not exhibit this issue with intellizone panels.