Oil Furnace Won't Accept New Role as Backup

[hiker88]

Hi everyone,

I've got an issue I would love to square away this weekend if I can. First, the setup
Froling 20\30
plumbed per Tarm schematic 2.12 square tank
Wired per Tarm BLT appendix (page 32-33) of plumbing schematic
Becket oil furnace w\ Honeywell l7224a aquastat and r7184a oil primary

If not in "wood only" mode and certain conditions are met, the blt control will supply 24vac to the tt switches on my oil furnace and allow it to start. Here's the thing though, my oil furnace is still firing in wood only mode. The oil furnace will fire when it hits the low limit set point.

I disconnected the wires from the TT switches on the oil furnace to troubleshot the issue, and those pins appear to always have 24vac on them. So obviously the blt controller can't stop the oil furnace from coming on if the oil furnace aquastat is providing 24vac.

So I think this is more of a "configuration" issue than a wiring thing with either my aquastat or primary on the oil furnace. I can set the oil furnace up for "cold start" but I don't know if that is the answer.

Any suggestions? I attached all the documentation I could think of in case it helps. Thank you for your time.

p.s. I couldn't seem to upload the plumbing schematic, so here is the link:
http://woodboilers.com/images/stories/documents/woodboilerplumbingschematic1211.pdf

 

[R Mannino]

you need to turn off the low limit on the 7224

 

[hiker88]

you need to turn off the low limit on the 7224

When I do that, I won't be able to use the oil furnace for dhw though right? In backup mode, the oil furnace will only come on when there is a call for heat from the thermostats.

Thank you.

 

[mikefrommaine]

Were the tt terminals on the 7184 jumpered or do they connect to something?

 

[hiker88]

Were the tt terminals on the 7184 jumpered or do they connect to something?

The TT terminals on the 7184 have always been jumpered to each other and I left it that way. Is that the culprit?

 

[mikefrommaine]

The TT terminals on the 7184 have always been jumpered to each other and I left it that way. Is that the culprit?

If you disconnect the jumper on the tt terminals than the burner should not fire. But everything else will still work (circulators etc.)

I believe you can connect the blt to these tt termials. In wood only mode the relay should open the tt connection. In oil mode the relay should be closed allowing the burner to run. You would have to remove the jumper for this to work.

 

[hiker88]

If you disconnect the jumper on the tt terminals than the burner should not fire. But everything else will still work (circulators etc.)

I believe you can connect the blt to these tt termials. In wood only mode the relay should open the tt connection. In oil mode the relay should be closed allowing the burner to run. You would have to remove the jumper for this to work.

So, remove the jumper from the 7184 tt connections. Then move the wires currently connected to the 7224 aquastat tt terminals to the 7184 tt terminals?

Just want to make sure I got it.

Thanks!

 

[mikefrommaine]

So, remove the jumper from the 7184 tt connections. Then move the wires currently connected to the 7224 aquastat tt terminals to the 7184 tt terminals?

Just want to make sure I got it.

Thanks!

Did you connect the blt to the 7224 tt terminals? I don't think that's where to make the connection.

If so I would remove the jumper on the 7184 tt terminals and connect the blt in its place. The blt would then open or make the connection between tt depending on what mode it is in.

The 7224 tt terminals should have been originally connected to a room thermostat or the end switches of a zone relay control. And I believe you would leave that alone.

 

[hiker88]

Did you connect the blt to the 7224 tt terminals? I don't think that's where to make the connection.

If so I would remove the jumper on the 7184 tt terminals and connect the blt in its place. The blt would then open or make the connection between tt depending on what mode it is in.

The 7224 tt terminals should have been originally connected to a room thermostat or the end switches of a zone relay control. And I believe you would leave that alone.

Mike,

It sounds like you know what you're talking about. Let me regroup on this and if you don't mind, I'll update tomorrow and maybe you can help me out. This will be after the Common Ground Fair of course

From what I understand, once the fire goes out in the Froling and storage goes below 140, my oil furnace is supposed to operate just like it always has. I think I'm close and missing something simple.

Thanks again.

 

[mikefrommaine]

That

Mike,

It sounds like you know what you're talking about. Let me regroup on this and if you don't mind, I'll update tomorrow and maybe you can help me out. This will be after the Common Ground Fair of course

From what I understand, once the fire goes out in the Froling and storage goes below 140, my oil furnace is supposed to operate just like it always has. I think I'm close and missing something simple.

Thanks again.

That's how I understand it to work when in auto mode. When in wood only mode the oil burner would not be able to turn on. To accomplish this relay cr2 in the blt takes the place of the jumper. Controling the ability of the oil burner to turn on depending on conditions or the mode you have set the blt in.

On my blt diagram it shows to connect terminals 7 and 8 of the blt to TT on the oil burner.

Im sure I could be explaining it better... Good luck with the traffic getting to the fair.

 

[R Mannino]

T and T on the 7224 are supposed to initiate a call for heat on the oil boiler.
If they are jumpered, someone doesn't know how to wire properly.

sounds like mikefromme has a grip on wiring

 

[hiker88]

Well,

After stepping back a bit, it appears to me the system is working by design.

If I leave the jumper on the oil furnace as it has always been (since 2006), the oil furnace is going to "over ride" for lack of a better term the BLT controller, and provide the 28 vac whenever the aquastat hits it low limit set point. This is not ideal, because I can have a situation in which the boiler will be running just to stay above the low limit, even if the Froling is going, or storage is above 140. It's not that it is a safety issue, its just a waste of oil.

Terminals 7 & 8 on the BLT are only hot with 28 vac when relay CR2 is energized. CR2 is only energized when there is a call for heat from the zones (in backup mode) or when there is a call for heat, and the storage aquastat is closed in Auto back up mode. This all works perfectly now.

So, back to the problem I'm trying to solve. I don't want to lose the ability to get dhw from the oil furnace during non heating times, say if someone like my wife needs hot water in a hurry. I also don't want the oil furnace running all the time to maintain its low limit set point.

What I think I will do is replace the jumper with a toggle. 99% of the time, the switch will be open putting the BLT in control of the system. If someone ever needs dhw in a hurry, they can close the toggle and allow the oil furnace to come on for dhw production.

Does that sounds logical\safe?

 

[mikefrommaine]

Isn't there a oil only setting on the blt? Which would leave cr2 energized and the oil functioning the same as always?

 

[hiker88]

Well, I just got off the phone w\Tarm and they've given me something to try. If this fixes it, it basically blows this whole thread out of the water which is a good thing. Every time I start to think I'm getting the hang of this stuff...

I'll try it out and update later. Thanks again.

 

[R Mannino]

Well, I just got off the phone w\Tarm and they've given me something to try. If this fixes it, it basically blows this whole thread out of the water which is a good thing. Every time I start to think I'm getting the hang of this stuff...

I'll try it out and update later. Thanks again.

If you break T-T on the 7184 oil primary the oil burner will never fire, ever, if it does the primary is bad. From the Tarm diagram it looks like that's how they want it wired.

 

[hiker88]

If you break T-T on the 7184 oil primary the oil burner will never fire, ever, if it does the primary is bad. From the Tarm diagram it looks like that's how they want it wired.

Yes, I moved the wires from the blt to the TT terminals on the primary after talking with Tarm. I had incorrectly left them on the aquastat TT terminals. You're correct that in that configuration the boiler will never fire if TTs are open.

The "problem" for lack of a better word, is that I have a tankless coil oil furnace, and I was hoping that when in backup only, or auto backup, that I could get my oil furnace to come on to maintain it's low limit set point (for dhw). However the blt is designed to close terminals 7 & 8 when there is a call for heat and storage is below its set point. This was a misunderstanding on my part.

But everything is working by design and I have an easy work around. All I need to do is put a toggle in parallel on blt terminals 7 & 8 so that I can close the TTs on the primary, thereby letting the oil furnace do its thing if I ever need dhw in a hurry during non heating seasons. I've tested this and it works perfectly now.

 

[mikefrommaine]

Glad you got it working.

How are making dhw when burning wood?

 

[Cross Cut Saw]

 

[hiker88]

Glad you got it working.

How are making dhw when burning wood?

I have a coil in the tank for that, but the system won't be totally online for another couple weeks; I have to finish the dump zone and a couple other things.

 

[hiker88]

I should probably change the title of this post now that I know what's going on...

 

[mikefrommaine]

I have a coil in the tank for that, but the system won't be totally online for another couple weeks; I have to finish the dump zone and a couple other things.

So without the manual override switch you are concerned you wouldn't have hot water when the wood boiler is going but storage is not up to temp yet?

Maybe you could use a low limit aquastat on the storage tank, wired in parallel with tt on the burner. It would open the tt connection whenever storage was above say 120. And close when it was below that. Basically the aquastat would take the place of the toggle. That way you wouldnt have to remember to do it manually.

 

[hiker88]

Maybe you could use a low limit aquastat on the storage tank, wired in parallel with tt on the burner. It would open the tt connection whenever storage was above say 120. And close when it was below that. Basically the aquastat would take the place of the toggle. That way you wouldnt have to remember to do it manually.

I think you're on to something there. It wouldn't take much to add another aquastat to the storage system. There's a close on rise to allow the oil furnace to provide heat when storage is below 140 - the other could be set at 120 like you said.

I gotta tell you though, I'm watching that other thread right now on the front page about electric hot water heaters - and with the price of oil already so high this season, an electric heater for dhw may be the way to go. It's really got me thinking.

 

[R Mannino]

Electric water heaters have terrible recovery rates.

The controls to setup the oil as backup are actually pretty simple, now that I know what's going on.