Originally posted by bruce_miranda
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'Vaillant HW Priority on EcoTec Pluses
The vaillant ecotec 6xx boiler can be used as a dual stat boiler.
Use swithched live on terminal 4 for CH demand.
Use a volt free contact to short the C1C2 plug on the harness (24V side) to take priority HW demand. Fit a Vaillant VR10 sensor to the orange and black wires of boiler harness to sense cylinder temperature.
On the first gen ecotecs the temps are set with the dials. On the later models with DIA interface then HW temp is set in the diagnostic parameters.
Never tried this with a VR33'
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