I have a dedicated 20 amp circuit powering my boiler's control unit. The control unit is basically a relay operated by the thermostat that 1) fires the boiler and 2) turns a circulating pump on and off. While the boiler and pump are on separate feeds coming out of the control unit, they are switched simultaneously so the pump operates only when the boiler is fired.
Twice this winter, a branch of the water circulation route froze. Each incident resulted in a $480 service call to thaw the line. This is unprecedented in my home. After the second time it happened, I disconnected the circulating pump from the relay and wired it directly so it would run continuously. That prevented further freezing incidents despite even colder temperatures. Now that warmer weather has returned, I put the pump back under relay control.
This is current state:
I want to find a permanently-installed way to switch the pump between relay control and continuous power. My thoughts are that this could be accomplished like so:
Note the DPDT switch wired "backwards" to control which line powers the pump.
My questions are:
- Is this feasible and safe?
- Can I do this with a SPDT switch just on the hot side (and wire all the common together)?
- Is there a better way?
- Are there products available which would let me accomplish this goal with WiFi control?
In response to questions in the comments, I have the following updates:
The control unit is a Honeywell. It says "Aquastat Relay Type L8148J". Below, I've included a photo of the actual uncovered unit and a diagram from the inside of the cover.
The whole house is on a single zone. A main artery in the basement distributes hot water. Each radiator is served by a pair of intersections. I'm not sure what they're called, but I've included a picture. They don't look like traditional valves to me.
The set of pipes that froze lead up an outside wall to a bedroom radiator.