Circulation pump woes Taco - 007‑F4

burnEmBoss

I have a hydronic / baseboard heating system that consists of a Burnham model P‑205A‑WNIH boiler with a side‑arm that has 4 zones. The system was installed in 1988, I believe, and I have only replaced the side‑arm tank, so she’s getting up there in age. (you can see in the photos it's been quite a project over the years!)

I woke up one morning and noticed that the downstairs zone was cold and had not reached its 68 °F setpoint on the Nest. I suspected the circulation pump because the temperature on each side of it was a lot lower than the water temperature going to the side‑arm. After swapping out the capacitor on the circulation pump (Taco 007‑F4), (think the F5 is newer version) there was no change in temperature. I measured the current going to it and saw zero amps, so it appears to be dead.

That seems like an easy fix, and as you can see it’s rusted badly, but I’m curious how the system is still working somewhat, as the radiators still seem to be heating the house. My research (the LLMs’) mentioned gravity circulation (a.k.a. thermosiphoning), but the water coming out of the boiler seems to be a lot cooler than the water going to the side‑arm.
Comments: am I on the right track here? Also, how should I bleed air out of my system after the pump replacement? (of course love to get a new boiler but 15k seems like a waste!)

hot_rod

Some creative wiring there, inside and outside the boiler😯

Are the zone valves on the return or supply piping?

If they are on the return, when the sidearm circ is running, it could push some flow to the zones. Of a very mild thermosiphon can be established. ZV are best on the supply to prevent either potential.

burnEmBoss

Yeah, I think the zone valves we figured out are on the return side. So I reconnected with my buddy who went to plumbing school and he helped me sort it out. Upgraded the flow to get a more modern circulation pump that they recommended and had lying around an Alpha 15-58. BT and an app!! Hopefully in the future, I can bribe him to help me install a nice wall mounted high-efficiency boiler! The quotes I’ve had have been like 7K for the install.

hot_rod

yep if the heaters are warm without the pump running for a period of time, somewhere you have a ghost flow condition.

The boiler should be a cold start on a low mass copper fin tube. If the boiler idles at temperature you have more potential to have heat migration.

How is the boiler sized to the radiation connected to it?