Heating, Air Conditioning, Fridge, HVAC/White Rodgers thermostat

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Question
QUESTION: I have 2 White Rodgers  model lE78-140 stats on a 3 zone radiant floor boiler system they do not seem to shut the boiler off when they reach the set temp.

ANSWER: Larry,

Briefly looked at the stat shows either milivolt or 24volt , possible you have the wrong stat. If it's 24 volt remove the  two wires from the stat  and see if your boiler shuts down if so then jumper together to see if it starts. Also typically boilers have there own aqua stat  to maintain the water temperature and the t-stat simply open and close the heat valve only and or turn on the circulator pump. Yo may have issues with your zone valve . Was the system working ok before you changed the stat, are these stat existing.

---------- FOLLOW-UP ----------

QUESTION: these two stats have been working since they were installed new in Nov. 2009. just this week they started acting up.  the stat tells the Taco S R 503 zone switching relay to turn the boiler on and the circulating pumps to run. Today the stat was set at 66  the room temp said 72 but this zone the boiler was still running and would not shut off. I turn the switch on the stat from heat to off to get the boiler to shut down.

Answer
Larry,

You would have to see if the switching relay is dropping out when the t-stat is satisfied , possible you have wiring issues that's keeping the relay energised, or possible the relay contact points are welded shut keeping the boiler running. Also what happened when you physically took the wires off the t- stat and jumper together to start the boiler can you hear the relay energizing / clicking ?  Let it run for a few minutes then remove jumper to see if the boiler and pump shuts off. If it does you have a bad t- stat. The t-stat says it's a two wire heat only. Does your circulator pump shut off when you remove the jumper also along with the boiler ? If you have a plug in relay(s) pull them off the panel and look closely to make sure the points are not welded closed. Typically those type of relays have clear plastic case to look at the inner workings of the relays , you also can try ( if you have more than one relay ) is to pull all the relays out and see if boiler runs, if not reinstall one at a time ( make sure t-stats are not calling ) I also looked at the configuration and it looks like your suppose to have three  t-stats For Three zones , you state you have Two thermostat for three zones .

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40+ years diversified experience.An HVAC/Refrigeration Self Employed Contractor since 1986. NATE Certifield. Answer questions pertaining to Residential and Commercial Air Conditioning , Warm Air Heating, Heat Pump systems.Mechanical and Electrical troubleshooting of these systems.Be as detailed as possible when describing problem.Packaged unit or split systems.No appliance questions.

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Installation and Troubleshooting, Mechanical and Electrical, in following areas, Refrigeration ( Walk In and Reach In Coolers and Freezers ) Commercial Roof Top and Packaged Heating/Cooling ( Natural Gas,Propane, Electric, and Heat Pumps ) Computer Room Air Conditoning Systems,Commercial Residential Packaged and Split Systems Air Conditoning and Heat Pumps.Warm Air Oil , Natural and Propane Gas Heating systems.

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Graduated from Private Technical School in 1975. An HVAC/Refrigeration Contractor . Have Unlimited Heating/Piping and Cooling Contractor License.Limited Sheetmetal Contractors License.NATE Certifield. York Certifield Master Heat Pump Technician 1986. Served 33 years combination Active Duty Air Force , Air Force Reserves and Air National Guard in the HVAC/Refrigeration Shop/Mechanical Shop. Troubleshooting/Installing HVAC/Refrigeration Equiptment Worldwide. Retiring in 2003 as a Senior NCO ,and a Mechanical Superintendent.

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