Boilers - Steam and Hot Water Systems - Wiring one pump from two signals ?

I have a coal boiler feeding my oil boiler with one one Grunfos 3 speed pump running 24/7 reverse flow through my oil boiler. I am trying to wire the pump to run only on a call from the oil burner B1 connection (with primary jumper unhooked) and also to run on a overheat call from the L4006b on the coal boiler. I have 3 zones, with pumps and a DHW coil on the oil boiler.

Let's call the pump between the two boilers a 'transfer pump', TP for short...

When you say that you have the 'primary jumper unhooked', I presume you are talking about the T T jumper on the oil burner primary control? And that you've done this to disable the oil burner from firing... correct?

And your idea is to only suck the heat out of the coal boiler when the oil boilers aquastat calls for heat, thus asserting B1?

And also to run on overheat of the coal boiler as a 'wild zone' to dump the excess heat?

Isn't that going to happen pretty much routinely? I mean, if you've got a fire going in the stoker, without constant circulation, isn't it going to overheat quickly, and regularly?

Or am I misunderstanding something?

Correct on the TT jumper and the overheat. My coal boiler is a small stoker 90k that will idle at a low temp. I have stopped the TP pump and watched the coal boiler at idle. The temp climbs very slowly and dont think the overheat will be a problem.

What is the 4006 overheat a'stat currently connected to?

I think I would have it connected in parallel with the largest heating zone thermostat, so that if it did overheat, not only would it power up the transfer pump, but ALSO circulate through a zone to remove the heat faster.

Have you got anything in place to act as a wild zone in the case of a power failure?

Right now it's connected to my largest zone. My plan was to use it on the TP pump and a 2nd 4006b (set higher) hooked to my largest zone. I have nothing in place for a power outage. I cant use a gravity set up, the coal boiler is about 7' higher in a coal storage/boiler room at ground level at the end of my raised ranch. A power outage will shut down the coal fire with in minutes. I am looking to save on coal usage in the warmer months and periods of no DHW use.

OK... let me just recap to see if I've got it all straight.

You want the TP to run in response to a call to the burner.

Theoretically, you could simply wire the TP directly to the B1 and B2 terminals, in parallel with the burner, since they are both 120 VAC devices. The caveat would be that you want to be sure the relay in the aquastat isn't going to be over-taxed... since you won't be running the burner when the pump is running, that's OK, and you could wire a switch in the line to the pump to shut it down when you are using the burner.

If you leave the 4006 wired to the largest zone, then that should call for the burner to fire up to high limit... let's see, will that work? maybe not... if the stoker is hot enough to satisfy the aquastat on the boiler, then the TP would shut down...

You might need to wire up another relay... say, an 8845...

my brain hurts! I have to think about this... chores to do, be back later.

I have a Taco 501 relay. Is it possible to wire it to run the pump from both a 120 vac and a low voltage signal?

Not really... it could be wired so that it would only respond to BOTH, AND, but not EITHER, OR...

Why not utilize the C1,C2 on the oiler aquastat to run the TP?

And leave the 4006 connected to the largest zone?

The TP would now run on ANY heat call from the home, AND it would run when the 4006 called overheat.

Would that acheive?

Maybe not... because you want to keep the oiler warm for the domestic coil... durnit, that would be too easy.

Isn't the 4006 rated for line voltage use?

So what if you ran 120 into the 4006...
Jumper the TT connection in the 501 so that it will trip when AC is applied to the L1 in the 501...
Run the 120AC out of the 4006 to to the L1 on the 501...
AND run the B1 from the oiler a'stat to the L1 on the 501...

You would need to use another a'stat for the largest zone.

You would have to be careful that you are using the SAME AC HOT leg if you did this.

thought food...

OK, another idea...

Using the 501.

Wire the SAME AC input to the 501 as the oiler.

Wire the 4006 to the TT input on the 501.

Wire the TP to ONE of the relay pairs in the 501.

Wire the N.O. contacts on the OTHER relay pair in the 501 to the largest zone.

So far, what you have is the TP running and the largest zone running on an overheat.

Next... Run a wire from B1 to the hot terminal on the TP.

Now, either B1 will run the TP to keep boiler warm, AND/OR the TP will run AND the largest zone will activate for overheat.

Think about this... if I get time, I'll draw a diagram.

If the TT jumper is re-connected on the oil primary, and the stoker overheats, the burner will fire. You might want to add a switch in that B1 line, and don't forget to switch it OFF when you reconnect the TT on the primary!

[ edit: while I was doing the drawing, I found a way around the problem of the burner firing when not wanted... but, you still need a switch so that the pump doesn't run when the burner is connected and firing, see post after the diagram for more on that]

Thanks for your time on this wiring project. A diagram in crayon for my electrically challenged brain would be very helpful. Here's a link to the Taco 501 for terminal #'s. http://www.taco-hvac.com/uploads/FileLibrary/SR501102-081.pdf Thanks again, Ed

Here's a drawing I came up with illustrating my idea, and I want to stress that it is an IDEA, based on only what I know of your system. It is fully up to you to determine it's suitability for your purpose, and I am not responsible if anything goes wrong! (standard disclaimer)

I noted on the drawing to watch out for pin numbers and wire according to the FUNCTION of the pins. This is very important!

http://i224.photobucket.com/albums/dd118/JeffPicks/efo141_501_relay.jpg?t=1256523047

You probably want to put a switch in the line to the transfer pump so that when you aren't buring coal, you can switch the pump off so it doesn't run every time the burner does.

Perfect diagram, thank you for all your time and effort on my hair brain wiring project. I am aware of the burner firing in a overheat situation if the primary jumper was in place. Would a simple relay solve that?(Never mind,Just figured out you fixed that problem)Either way there will be a switch in that line. Thanks again, Ed

Just look it over real good, understand how it works, and then decide if it's really what you need. Please don't take my word for it!

And if anyone else sees anything wrong, please say so!