Trane Furnace Thermostat Went Blank in a Cypress Home — Float Switch Was the Culprit

When a Cypress homeowner noticed their upstairs thermostat was completely blank, they knew something wasn’t right—especially during heating season. The home is equipped with a 2019 Trane 95% high-efficiency gas furnace, so our team was called out to diagnose the issue. Upon arrival, we found that 24 volts of power were present at the furnace’s R terminal, which told us the transformer was working properly. However, that voltage was not making it through the condensate float safety switch, a common protection device designed to shut the system down if water backs up in the drain line. To confirm the diagnosis, we temporarily bypassed the float switch for testing, and the Ecobee thermostat immediately powered back on. This confirmed a failed float switch. We replaced the faulty condensate float switch, restored normal wiring, and thoroughly tested the system. The upstairs Trane furnace started up and operated normally once repairs were complete. Cypress homeowner takeaway: If your thermostat suddenly goes blank, the issue isn’t always the thermostat itself. Condensate float switches are a common safety shutdown point, especially in high-efficiency systems. Regular maintenance can catch these issues before they leave part of your home without heat.