Boiler Controls...

Ishmael

Just out of curiosity: I've never wired a boiler; I usually leave that for the electrician. But I was just wondering if anyone can explain what is the function of the low voltage "end switch" terminals on a typical boiler control (such as Taco).

mdshunk

An inducer fan has a centrifugal switch on the end of the housing. When it's up to speed, the "end switch" contacts make to prove that the inducer fan is running.

That's one type of end switch, anyhow.

PIPES

Hey Ish, the end switch in a Taco control is a set of dry contacts(no voltage ) which changes state(makes contact) when any zone calls. Normally you wire to T T on your triple aquastat.

Ishmael

Thanks. So, when a zone calls and the end switch makes contact, what exactly is it "telling" the boiler to do? I'm only asking because I had to do a no heat service call (that I didn't really have time for) and I ended-up just splicing the TT wires in the boiler (Weil-McLain GV3) together and got it running for them. I watched it get up to temperature, flame cut-out and started back up again when return water temp got low enough. I told the builder (nobody living there yet) it's not really "right", but it'll be fine until the electrician has time to check out the Taco and low water cut-off to see what exactly the problem is. I ran into the electrician, told him what I did and he said, "Oh...that's perfect...now I don't have to rush over there...that's fine".

So...long story even longer: My question is (I guess) Why is the connection between the triple aquastat and the end switch even necessary?

PIPES

Ish, when you have a single zone boiler , the t-stat tells the boiler to circulate and fire if not up to temp. In a multi zone boiler you wire your t-stats to the cirulator control. Now your t-stats talk to your zone control and not to your aquastat, that's where the "end switch" comes in. It is the one talking to your aquastat letting it know there is a call for heat.
So what you did on your service call was to give the aquastat a constant call for heat, turning a cold start boiler into a warm start boiler.
Hope that helps you understand, I'll be glad to help more if you need.

Ishmael

That's great, Pipes. It makes a lot of sense, now. Thanks for your help.