I finally got my sidearm hooked back up in it's new location the evening before last. Much better, took my hot water tank from 115 up to 140 before I went to bed. Awesome. Last night before I went to bed, I put the last load in the boiler and happened to glance at my boiler temp before turning my back on it. 200°. Hmm - hadn't seen it that hot before. So I watched for a while and it was still creeping up. My storage was only 175 at top and not moving. Minor panic. I upped the speed to 2 on the loading unit. No change. Then I remembered what I did the night before and started putting 2 & 2 together - the flow was prioritizing through the 1" sidearm piping and going right back to the boiler with not much heat taken out of it. I throttled down a ball valve on that circuit some & things started easing up and storage started taking heat. I have a zone valve in that circuit that gets power from an aquastat feed that used to power my old damper door. So I turned that down a little bit from the 200 it was at before & the zone valve closed - so I should be good now (not sure why it didn't already cut out at 200, but anyway). I have the zone valve also wired through an electric heater thermostat tied on the outlet of the water heater that is supposed to close the zone valve when it sees temps above 120. But it's a flat surface on a round 3/4 valve body, so it's not feeling the heat like it should to work right. So, more tinkering to do yet - but I'm some glad I took a last second glance at my temp guage before I went to bed, although I'm pretty sure my dump circuit would have handled it OK. Actually, it might already have the first night & I didn't even know it.