Vaillant ecoTEC Plus 637 with ST9400C programmer

23 Oct 2011
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United Kingdom
:confused: Hi, I have this boiler for 3 years and is working great since 2 weeks ago when we had a power outage and I noticed that I was not getting hot water, so I switched it off and tuned on, all was ok but when I turn the heating on nothing happens; So I did my own investigation and found that I can only turn on the system selected first for eg. CH first followed by HW on the programmer and vice versa but I cannot get BOTh CH & HW to come on together, can anyone help as to what is the cause of this !! Normally I hear a click when I slelct both modes but I hear only the first click but not the second, could it be a programmer fault ??
( I checked the Cylinder stat & room stat they work ok).
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