trouble/shoot

4 JULY 2011
[editor's update 8/27/11: several weeks back, I discovered through some well-targeted trouble shooting with Dan Leonard, that the SOM7 control had a variable speed setting for the pump in question. It was not busted, but was set to run at only 30% power. The solution was a matter of increasing the equilibrium pump power to 100%.] 

 So I may have detected the reason that we've been hearing the boiler cycle in the last (hot, and sunny) month of June. One of the pumps in the solar system has probably failed. There are two pumps: one brings hot antifreeze (see post from 2/13/11 for more on this) from the rooftop down to the heat-exchange coil in the solar tank, and the other is used to move heat into the primary tank, when the solar tank gets hot, but there's no load to draw hot water out of it. The second pump allows heating all of the combined volume of the two tanks to equilibrium, more or less.

So if the “equilibrating” pump were not working, what happens? On a sunny day (like the 2nd of July) we'd see the solar tank heating right up (137F +), but the primary tank, not heating (hovering at 113F). Several things point to a pump failure:

1) there's no whirring sound coming from the pump, when the relay says it's running
2) the boiler has been kicking on every once and a while, meaning a gas bill in June (arrgh!)
3) the temperatures observed above
4) the controller's record shows that the solar pump has been running much less than the equilibrium pump.

Here's a chicken scratch schematic of how it works, and where the pumps are.



Thanks to Dan Comeau for remembering the isolation valves on either side of that pump, making the switch out fairly easy, if need be.

Then again, I just went down to replace the pump, and found the pump whirring away! Why I don't yet know. Will have to give this one another look see. As of 7-4-2011, the pump once again appeared defunkt.