Another Hive Wiring Issue...Gravity Fed Dandoss 103 to Dual channel Hive

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If you want any more information there's loads on the web if you search 'Y-Plan' or 'S-Plan'.

Either would work for you, but Y-Plan system that uses a single 3-Port valve (Mid Position Valve) is probably the most common solution.

FULLY PUMPED SYSTEM

You can replace the Danfoss with a more modern single channel timeswitch / programmer, but it won't change how the system operates. The restriction is down to the plumbing.