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Steam/Thermosta/24V AC question
Howdy. recently converted my old steam boiler from oil to natural gas w/ a new carlin burner. the ignition unit pushes 24v AC on a two wire run to the thermostat. as part of these changes to my heating system, i've been trying to use a new nest thermostat and am having issues.
the thermostat will work for a while and then fail in a replicable manner. doesn't generate formal errors, just starts acting erratically and then fails to make heat calls to the boiler after 12-24hrs. after lengthy troubleshooting w/ nest i returned one and the replacement unit behaved in identical fashion. worked well for a period, then showed escalating and remarkably similar irregularities and eventually failed to make appropriate thermostatic boiler fire calls.
im consistently reading 29.47 on the line, rather than 24. nest claims that this is just barely outside the tolerance of their device for power variance and is the likely culprit; not enough for it to trip device burnout or linepower codes, but enough to create wonky behavior. given that i've been able to replicate the behavior in predictable fashion, and working in tech with an appreciation for how potentially complex/persnickety the internal integrations within the device are, i'm inclined to think this is at least a possibility.
that said, my questions are:
-has anyone encountered a similar situation
-my boiler tech tells me that a 29V read is actually pretty standard and that significant swings in the output from a 24V ignition control box are pretty standard. this sound accurate?
-given that it's AC, my assumption is that there's no simple rectifier or other inline solution to step-down or govern the power coming to the thermostat. any suggestions?
-anyone know how this device actually works on a two line system? as it has an internal battery, wouldn't it be converting the power and thus conditioning it for itself anyway.
-how does the power/ boiler call loop work on two wire?
assuming that my boiler guy is dead on and that AC power is typically rather dirty and with great variance, i have a hard time believing that the nest engineers wouldn't have taken that into account and designed greater tolerance for variance into their platform.
thanks much in advance for your time and experience.
Nest 2nd Generation
Carlin 60200-02FR Ignition Gas primary
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