As part of the pump install I changed the wiring again. In the past I had trouble with the primary and secondary pumps working independently. I thought that was one of the things that wore out the Taco 011 pump the first time. I thought it was running when the primary pump was not and when the valves were closed.
The Taco Zone Controller sends a signal to the boiler when the zone valve opens. The zone valves open when the thermostat calls for heat. I think the valve opens and then sends the end switch signal back to the controller which then turns on the boiler.
The boiler has a control for the primary pump. It tells the pump to come on as soon as the boiler sends it a signal. It also remains on for a minute or two after the boiler goes off. The zone controller sends a signal to the secondary pump to come on when it sends the boiler signal. So the secondary pump comes on a bit before the boiler because the boiler has to go through a pre-heat setting. I thought that was keeping the two pumps from running synchronously. Although I forgot about it, reading the former post reminded me that the secondary pump coming on first was causing a low pressure error in the boiler.
But when I wired the new pump, it seemed that it would be easier to wire the primary pump back at the boiler. The electrical box on the Grundfos is not as large as the one on the Taco and I was having difficulty fitting in all the wires. So I eliminated the one to the boiler pump and wired it back at the boiler itself. Now the entire system seems to work just fine. This smaller pump is not causing low pressure in the primary loop.
Here is the Taco illustration of their recommended wiring for a system and domestic hot water pump. I am only using the system pump and not the priority zone 6 to store hot water.
The diagram is a little different from the actual board. Here is a demonstration of the system pump wiring also with a domestic hot water pump.
I have the jumper installed even though I’m not using Zone 6. But the secondary pump is wired to the first two posts, the pump end switch on the board. I’m not sure why this seems to be working when it didn’t before so I’ll have to keep an eye on it.