Arrived on site to perform diagnostic on 4 year old Lennox system. System was not installed by us, was installed by Action Air. Homeowner states that thermostat was coming and going on a full white screen and would not allow her to control thermostat. Now the thermostat is completely blank and cannot be controlled. Tried resetting thermostat and still did not work. Thermostat needs to be replaced. Unfortunately white I comfort thermostat is no longer available, need to upgrade thermostat to an s30 thermostat. Thermostat is still under warranty, labor and warranty processing is not. Spoke to Dave to approve price given. Need to return with S30 thermostat and PCO Maintenance filtration kit and install new thermostat and replace filtration kit. Unfortunately Homeowners husband is going through medical situations and cannot go without heat. Wired in a temporary thermostat for homeowner to have heat until we return and complete thermostat replacement. System is operational in heat mode up