Hi- I have an older home with two separate one-zone, gas-fired boilers (the house used to be a two family, so there's one boiler for each floor). At the start of the heating season, I turned on both boilers, and they were working fine. A few days later, I replaced the old honeywell manual thermostats with programmable ones, and still, both systems were working fine. Then, two days ago, the upstairs stopped getting heat at all. The thermostat will call for heat (you can hear the click, and the "heat" icon shows up on it), but none comes up. The burner comes on, and the pipe emerging from the boiler gets hot, but once it gets past the expansion tank, is stone cold. Any ideas? Thanks!

 

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