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Old 03-13-22, 11:15 PM   #21
Solar Mike
Helper EcoRenovator
 
Join Date: Apr 2010
Location: Wellington, New Zealand
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Had the same issue when I built my flat plate Solar Hot Water panels and mounted them on the roof, on a cold night the quick lowering of water temperature in the panels would initiate reverse thermo-syphoning out of the hot water cylinder tank.

Fixed by inserting an all brass water swing valve in the line to the panels, place it slightly angled so the weight of the internal valve flap closes fully when the pump has turned off.

Cheers
Mike

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