Steam Boiler and Power Stealing?

Mel_3

I had been running an old Weil Mclain steam boiler using a Honeywell Chronotherm IV power stealing thermostat, and happy not to worry about batteries though it did go blank when either the pressuretrol cut off or the water level cutoff interrupted the heating.  When the pressure went down or the water level went up the thermostat would come back on.  No big deal.  The programming stayed intact.



I just had a new Weil Mclain EG40 PIDN-S 125,000 BTU steam boiler with an electronic ignition installed and I am told it will not support the power stealing thermostat.  Can this be?  Do I have to use a battery powered thermostat?



Any advice appreciated.



Mel

Jamie Hall

Yes and no

Your old thermostat requires 24 vac to operate, hence "power stealing".  It got its power from the boiler control circuitry..  Many new boiler controls will not tolerate that; if your new boiler controls say they won't, they probably mean it.



However -- you can either provide an independent 24 vac source for your existing thermostat, or replace it with a new, battery powered one which does the same things your existing one did.