Well, it seems I have enough pump capacity and not enough hx capacity
Just checked the end of my 4 hour burn. Tank is at 188. That's up 16 degrees, 3 more than yesterday.
And to be fair, the hotter the tank gets, the slower it wants to heat up. And, at those tank temps I noticed the boiler went into idle mode. Not sure when, but it was idling at about 3 hours and 45 minutes. That really limits the rate of heating the tank, too.
To be fair, I'd have to repeat this test next week, trying to start with the tank temp down around 160.
Two points of concern -
First - the pump off the boiler did manage to push through the pex, pump in the basement, and the two flat plate hx in the basement. I closed a valve in the basement to get a fair test with no losses to the ground.
Second - with the path the way it is in the boiler shed, the basement pump can either pull through the coils in the tank or pull through the boiler. They are essentially in parallel. Check valves won't help, because the water is always flowing the same direction.
The first problem I can solve with a valve that opens only when the pump runs. (Any recommendations on a good 1 inch valve to work off of 110 VAC?)
The second problem is a whole lot more difficult. I didn't plan on adding an automated valve there, and I have about 4 inches to work with.
Here's a thought - Does anyone make actuators to fit on the stems of 1 inch ball valves? I know for larger industrial valves it's easy to get actuators that just fit on the stem. No need to replace a valve when you want to automate one. That would make my life soooo easy!