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Help needed: Connecting Ecobee Smart Thermostat to a European oil-fired central heating boiler

iggythebrushiggythebrush SwitzerlandMember

Hello and Happy New Year!

I have been trying to work out how to connect my Ecobee to my combination central heating and domestic hot water boiler, which is an oil-fired 18kW Oertli KUSN140 with an integrated RDD-110B central heating/DHW controller from around 2002 connected to high temperature radiators.

The RDD-110B only has inputs for 3-wire analogue thermistor room stats and the boiler needs to be operational all the time for domestic hot water, so I cannot control the boiler itself from the Ecobee. Am I right in thinking that the only possible approach is to connect an external 24VAC relay to the equipment interface heat and return outputs, and to use the relay to switch mains 230VAC to the heating circulation pump, or will that cause potential problems with pump overrun requirements for the boiler?

Any help or previous experience greatly appreciated!



  • dborndborn Montreal, CanadaMember

    I have no experience with your type of equipment but if it was me, I would connect the circulation pump as the "fan" as it does essentially the same thing but with water instead of air. As you can adjust the time the pump/fan runs after the call for heat is completed, this should be ok? I also think external 24VAC relay should be okay to control the circulation pump.

    So if I understand correctly, the boiler runs from its own internal thermostat which either only keeps the hot water hot or when the circulation pump is turned on, it then heats your house? If this is the case, you're probably better off just powering the circulation pump as the "furnace" itself.

    Good luck with your project,

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