Question about Honeywell Programmable Thermostat Heater

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Honeywell ST6400C - hot water not working

I have a Honeywell ST6400C and while the heating works perfectly normally (firing up the boiler on command etc) the hot water light refuses to come on & we are now without hot water.  I have tried resetting both the boiler & the ST6400C and am out of ideas.  Please note I am not a plumber so please explain any solutions in very simple words!!
Does anyone have any ideas?  Many thanks!

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  • bluecoppice May 10, 2009

    Thanks for the response.  The ST6400C was installed at the same time as the hot water system/boiler etc in 2007 and has been working fine until now.  All very strange!  


    The immersion heater is working fine so we have hot water but it is more expensive to run so any ideas would be greatly appreciated :-)

  • Anonymous Mar 19, 2014

    having problem with unburnt fuel in chamber of oil fired hot water boiler

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Some digital thermostats do no not work with zone valves is this a new thermostat that you had installed

Posted on May 10, 2009

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