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Posted by HeatPro on April 08, 2005 at 09:02:53:
In Reply to: Vaillant Boiler - Fault F.20 Over heat cut off activitated posted by hannah on April 08, 2005 at 04:29:23:
Water flow through the boiler has dropped to the point where the high temperature limit has stopped the burner before damage. Check that there is sufficient flow, no clogs, check for a good circulator and that there is a 30F degree rise or less in temperature from the point water enters the boiler and leaves the boiler at all times.