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st6400c

  1. R

    Honeywell ST6400C Programmer reboots itself when CH+HW programs turn on

    Hi - I have inherited an old ST6400C when we moved in 7 years ago. I'd guess its 15 years old looking at the agr of the boiler etc. Generally been working OK but I recently replaced the mechanical dial wired thermostat ( see pic ) with a meross mts200b ( see pic ). Since then ( it may only be...
  2. silverfox2019

    How do I set the two programmers on my CH+HW system

    The CH+HW system in my new home has a programmable room stat (a Honeywell CM921) downstairs and a 7 day programmer (a Honeywell ST6400c) upstairs in the airing cupboard housing the HW cylinder. I'm wondering how best to set the CH on periods for the times I choose. For example, is it best to...
  3. Ash D

    Replace Honeywell ST6400C With Nest

    Hello all, Now that I’ve had an unvented cylinder fitted, I’m considering having a Google Nest (3rd Generation) thermostat fitted. I’ve read a few threads on here by others who also wanted to replace a Honeywell ST6400C controller (with room thermostat, hot water cylinder thermostat and a heat...
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