After turning off the DHW tap, my Ace High boiler stays in Hot Water mode - this also heats up the radiators. Some time ago I had to replace the DHW flow assembly diaphragm because the hot water would not turn on - could this be related? The operator pin that activates the DHW flow switch seems slow when returning, therefore keeping the hot water on. If not the diaphragm, could it be the diverter assembly that needs a replacement service kit?

DCW, April 2010

Did you sort this out?? My halstead high ace is doing exactly the same thing. Started a couple of days ago with the DHW not firing the boiler so assumed the diaphragm, but today has developed into the symptoms you state above. Any help appreciated.

Dave, November 2010