Crazy Troubleshooting Video

[drcampbell]

Using line voltage for control circuits does eliminate one cost item and point of failure: the transformer.
I don't have a problem with line-voltage thermostats, if everything's designed for it. We certainly use them here.
But I certainly do prefer that whatever the voltage, it originate in the appliance and there be one disconnect that renders the entire system safe.

I don't know whether multiple circuits is standard practice east of the pond, or it's also considered a violation/hack job there. Any Brits care to chime in?

 

[jaggedben]

Using line voltage for control circuits does eliminate one cost item and point of failure: the transformer.
I don't have a problem with line-voltage thermostats, if everything's designed for it. We certainly use them here.
But I certainly do prefer that whatever the voltage, it originate in the appliance and there be one disconnect that renders the entire system safe.

If the control circuit truly originates in the appliance the then it's a lot harder to miswire like this. If the appliance simply has terminals that pass through line voltage then someone who knows enough to be dangerous can always create a situation like in the video. I mean, clearly whoever wired that up didn't read the directions. So I suppose it's about the degree to which anyone designing a product must assume that if someone can wire something up unsafely without too much effort then they will.

 

[hbiss]

And some wonder why I criticize the British.

My guess is that it was designed that way to be backward compatible with the old boiler that was powered entirely through the line voltage thermostat. This one needed constant power so they just used the thermostat circuit as the control.

Hey, if you are going to have ring wiring why not?

-Hal