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Old 03-13-22, 11:15 PM   #21
Solar Mike
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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.

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Mike

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Old 03-14-22, 03:21 PM   #22
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Quote:
Originally Posted by JRMichler View Post
A simple check valve has a metal disk. The weight of that disk is probably enough to stop convection flow. I suggest just adding a check valve after the pump. I would not use a check valve with a spring because residential hydronic circulating pumps are low head pumps - they create very low pressure. The pressure needed to push the spring open will reduce flow, and could completely stop the flow.
I had a spring-loaded check valve in my spare parts, so I installed it today.
And you were right: The spring is too much for the circulation pump. Even on the highest of the 3 speeds it made strange sounds and hardly moved any water - it barely pulled any hot water out of the tank, after 30-40 minutes the radiators on the ground floor were still cold.

So, I took out the check valve, but did add a heat trap (looping up about 20-30cm above the hot water exit), so I'll see how that works. Its placement is not ideal (after the thermal mixing valve, should be before it), but in the summer I might clean that up and add a non-spring check valve if I decide to add the old tank in parallel.
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Old 04-27-22, 02:46 PM   #23
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Update.
I read about heat traps and concocted something like this:

The heat trap goes up ~35cm, then down ~20cm, through the pump and up to the radiators. The heat trap is above the mixing valve. Could this be the reason why it doesn't work? The heat still siphons up through the pump and to the radiators
Here is a simple diagram:


During the summer I plan to rework this so that the heat trap is before the mixing valve. Since the low ceiling limits the height if the heat trap goes up above the tank, then can it go down, like this?


If this will work, how low should it go?

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