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waste oil heater / Honeywell TF834.3

Discussion in 'Electrics UK' started by SparkyTris, 16 Nov 2020.

  1. SparkyTris


    24 Nov 2004
    Thanks Received:
    United Kingdom
    anybody got any experience with waste oil heater control boxes?
    namely in this case, Honeywell TF834.3 (rebranded as satronic among others)
    My question is regarding the oil preheater, and how it is supposed to be controlled.
    The datasheet of this module shows timing diagrams on p.3
    Terminal 6 of the controller appears to provide line power ("Phase" in the data sheet) to the preheater element; all the time. the application circuit shows no thermostatic control to the heater.... ???
    there *is* a thermostatic switch (labelled FT in the schematics) which is a NO switch. it closes when the oil in the preheat tank gets hot, which in turn puts Phase onto pin 4 in order to power the blower and signal the igniter to start. Effectively this thermostatic switch ensures that the burner will not fire if the oil is too cool.
    However this thermostatic switch will not stop the heater if the oil gets too hot.
    Clearly it is possible to set up independent thermostatic control of the heater simply by placing a NC thermoswitch in series with the heater circuit but this is not shown on the application diagram.

    The NO thermoswitch I reference above which is the hot-oil-ready sensor, is part of a 3-pole thermostat built in to the preheat tank, so the facility to provide control of the upper temp of the fuel is readily available, it's just not detailed in the data sheet which seems strange (?)

    This question came about over a waste oil heater which the owner had started rebuilding part of, and then realised he hadnt taken sufficient notes of what he had un-wired. but most of the wiring was intact and he assures me that it was "like that from new", and as far as I can see, there was no upper limit control implemented, so the oil would surely have boiled. I must be getting something wrong.
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