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Posted by HeatPro on November 24, 2006 at 10:41:22:
In Reply to: valliant 242e DHW not firing up posted by Roger on November 24, 2006 at 08:25:58:
My Valliant 242e does not fire up when DHW is called for.
: It works fine on CH and when CH is on there is DHW no problem, but it does not go thro the routine of shutting down and refiring up for DHW ... also the light for DHW is out.
: I have been told that the diverter vlave is at fualt but I an not sure this is true..
: What is the device that recogises the DHW demand and fires the sysytem up?
: Surely this is a pressure drop device ?
: Pressure differential valve and Servo Valve are both listed as parts .. is either of these the gadget that turns on the system when DHW is demanded ??
+++ You are on the right track. No guarantee that the diverter valve is at fault; but just about the only way that the heater will know that there is a demand for hot water is to have the domestic water pressure overcome the system pressure through a diverter valve and sensor. Diverter valves fail to operate because of the major weakness of tankless heaters - that of hard water liming up the motion of closely made parts that move. That's why the manufacturers recommend yearly refurbishment.