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Old 03-14-22, 03:21 PM   #22
Piwoslaw
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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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