Boiler Control with Hand Off Auto Switches

Hi all, I'm looking at building a control panel for my boiler that allows me to override all the components on their own with hand off auto switches. I am trying to have green pilot lights lit when the everything is in auto mode, and if I override something I want a red light to illuminate for that function. Could everyone take a look at the attached wiring diagram and see if I made any mistakes in the wiring to where the boiler is not going to operate properly with what I am trying to do? Thanks!

Looks Good!

You may find a ON pilot light to be a handy item wired to the Timer Switched wire-ZR and a neutral.

I'm not sure that is the best way to wire your setup. In auto mode, at high limit, your pump would shut down. Not sure that is what you want to do. Pump should stay running on a "call" for heat. The 120volt relay that powers the pump,airhandler, and stoker, keeps them all from running on a high limit. You want your pump and air handler to stay running but not the stoker.

McGiever, thats a good idea. I'll have to add that in.

Scottscoaled, I was trying to avoid that happening. The way its wired (at least what I intended) was for the call for the pump and the AH to come off the circualtor terminals on the aquastat. The c1 and c2 terminals are what provide the pull in the 120v contactor. The contactor in turn gives power to the pump and AH. The stoker is powered directly off the burner terminal B1 and B2 through the LWCO. Would this not keep the pump and AH running if the temp goes over high limit or am I misunderstanding the way the aquastat functions?

Listen to Scottscoaled,

Your violating the first and only operating principle for small stokers of K.I.S.S.(keep it simple son). That's why I got rid of the digital boiler controls and good riddance!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

You need to be able to let the circulator run independently to dump heat at all times.

jibs1723 wrote: ↑

Wed. Oct. 30, 2019 7:51 am

Scottscoaled, I was trying to avoid that happening. The way its wired (at least what I intended) was for the call for the pump and the AH to come off the circualtor terminals on the aquastat. The c1 and c2 terminals are what provide the pull in the 120v contactor. The contactor in turn gives power to the pump and AH. The stoker is powered directly off the burner terminal B1 and B2 through the LWCO. Would this not keep the pump and AH running if the temp goes over high limit or am I misunderstanding the way the aquastat functions?

Scott brings up a valid point. The aquastat C1, C2 will not provide any power to the 120v contactor after a heat call is satisfied or upon hitting the high limit. How otherwise would they ever cycle off automatically?. So this leaves no power to the pump and air handler after being cycled off.

And typically a LWCO kills all power from the supply source. It is the High/High Limit "dump" circuit that takes over the duty of killing just the stoker's and timer's power to stop any minor or major boiler heat over runs.

As for a independent fail safe High/High Limit "dump zone" circuit being employed in the event of a burner over run, there needs to be another separate aquastat control with a constant source of power from ahead or before the L8124 Aquastat to maintain the power to the pump and air handler so to be able to "dump" or shed excess heat, if activated, down to a point below set point and to also at the same time to totally remove the power source for the stoker and timer. A properly placed separate aquastat which employs a SPDT contact could handle all this.

McGiever wrote: ↑

Wed. Oct. 30, 2019 12:14 pm

Scott brings up a valid point. The aquastat C1, C2 will not provide any power to the 120v contactor after a heat call is satisfied or upon hitting the high limit. How otherwise would they ever cycle off automatically?. So this leaves no power to the pump and air handler after being cycled off.

Maybe I'm not understanding the issue here. When the boiler hits high limit, the stoker will shut down but C1&C2 will remain energized, therefore keeping the pump and fan running if there is a call for heat. If the call satisfies then the pump and fan will shut down. At least that is my understanding from the manual. The dump zone is another separate conversation as that doesn't interact with the L8124 aquastat. If that were added, I would just run the hot wire through the 3rd contact on the fan and pump switches which would energize them.
A little background on the setup, it is a gentleman janitor mated to a hot water coil with a blower in my garage. I ran it all last year without a high limit and I never had any issues with overshoot. The HWC thermosyphons a fair bit due to the lack of a check valve or zone valve and the proximity to the boiler. I did this on purpose just to ensure the coil never gets too cold if there is no call for a long time. (garage wasn't insulated last year. Flat roof with coil mounted 1' below.

McGiever wrote: ↑

Wed. Oct. 30, 2019 12:14 pm

And typically a LWCO kills all power from the supply source. It is the High/High Limit "dump" circuit that takes over the duty of killing just the stoker's and timer's power to stop any minor or major boiler heat over runs.

Ahh understood, I will place that prior to the L8124. I thought that if the boiler was over the high limit temp the stoker was disabled even if there is power applied to ZR from the timer? I'm pretty sure thats how it worked last year but I could be mistaken.

McGiever wrote: ↑

Wed. Oct. 30, 2019 12:14 pm

As for a independent fail safe High/High Limit "dump zone" circuit being employed in the event of a burner over run, there needs to be another separate aquastat control with a constant source of power from ahead or before the L8124 Aquastat to maintain the power to the pump and air handler so to be able to "dump" or shed excess heat, if activated, down to a point below set point and to also at the same time to totally remove the power source for the stoker and timer. A properly placed separate aquastat which employs a SPDT contact could handle all this.

I am not opposed to adding a dump zone aquastat, but my difficulty is that I don't have any large taps on the boiler where I could put an aquastat well without having to removed a large 2+" pipe plug. I already did that once to open up both return ports, but I don't really want to push my luck doing it again. I could 100% see having a dump zone if I was using the boiler for domestic water or had some small zones on it, but since I have a coil that is sized to match the output of the boiler I haven't seen any issues. Is that uncommon? I understand the dump zone on a hand fired, but with a stoker what is the protection for? Just overshoots or if a contact burns closed and the stoker will not shut down?

Thanks for all the replies! This is exactly the kind of feedback I was looking for.

Okay, I see now, contactor from aquastat C1, C2 makes just the air handler and pump Auto run same as the aquastat alone would. Really no difference with that contactor.

Then with the Manual Bypass, always having a different constant power source that is away from the aquastat, can "force" any of the 3 motors to run when any would be selected.

The separate issue of the "dump" switch is that comes along sometimes built-in to the High,High Limit aquastat, and as you have experienced with your particular set up might not be warranted. But the High,High Limit portion is the fail-safe backup for a aquastat or timer with having a contact failed closed and HHL is the last line of defense for a "run-away" boiler, that is next to a LWCO it there were one.

I made a mistake. It was 345 in the morning. Jibs is right. I didn't see the cc terminals clearly. My bad. Good idea with the over rides.

jibs1723 wrote: ↑

Wed. Oct. 30, 2019 1:29 pm

I am not opposed to adding a dump zone aquastat, but my difficulty is that I don't have any large taps on the boiler where I could put an aquastat well without having to removed a large 2+" pipe plug. I already did that once to open up both return ports, but I don't really want to push my luck doing it again. I could 100% see having a dump zone if I was using the boiler for domestic water or had some small zones on it, but since I have a coil that is sized to match the output of the boiler I haven't seen any issues. Is that uncommon? I understand the dump zone on a hand fired, but with a stoker what is the protection for? Just overshoots or if a contact burns closed and the stoker will not shut down?

If one wanted a aquastat w/o having the well for it they could use a strap on aquastat on the supply pipe close to the vessel.

Scottscoaled wrote: ↑

Wed. Oct. 30, 2019 8:07 pm

I made a mistake. It was 345 in the morning. Jibs is right. I didn't see the cc terminals clearly. My bad. Good idea with the over rides.

No worries! I'm a mechanical engineer, not an electrical so excuse the messy schematic that is hard to follow.

McGiever wrote: ↑

Wed. Oct. 30, 2019 10:40 pm

If one wanted a aquastat w/o having the well for it they could use a strap on aquastat on the supply pipe close to the vessel.

I was actually thinking of doing something like that, what would a suggest temp be for that? Like 205 or there about's? I used a snap action disc thermostat to run the blower for the air handler for a while and it worked well. Something like that with normally closed contacts that open with temp rise would shut all power down if the pipe got too hot. With manual reset as well would be good. Nice and simple.

A strap on aquastst could be adjusted, the snap switch you need to find other ways to make it see different setting.

The manual reset would not keep the fire from going out, but then you'll never fill the burner with raw coal at least.

Well, life gets busy but finally got around to building this! Didn't end up exactly as designed, but it works great. I was in a hurry to get the boiler fired up for the first time after the controls install and didn't hook up the timer initially, and its been running for going on a month now without any outfires and no timer. I think the boiler loses temperature quickly enough in the garage (50f) when the heat isn't on that I haven't had an issue. I do think though that it takes longer to recover since the fire is so small but with the overrides I can turn the pump and unit heaters on even if the aquastat says no so it hasn't bothered me. Still need to neaten up the wires a bit, but you get the point. Thanks again for all the help

Nice Job!!

Next try adding a Carbon Monoxide Detector and perhaps a Smoke Detector that when triggered opens a contact that shuts down burner and another contact sends a remote alarm or dials a phone.

Pets that are home alone will love you for the CO & Smoke alarms burner shut down.

Thanks!

Would definitely do that if it was in the house. But this boiler is in the garage and only heats the garage. There is a CO/Smoke in there but I figure that's enough. Don't want the boiler shutting down when I run something for a couple mins too much haha