Running Thermostat off low limit

So I'm home all day watching the kids...what do I have to do except been on the coal website?
In these shoulder days I've had a few outfires, here's why:
Boiler temp < High limit + Fire very low
Thermostat call
Fire gets warmed up to operating conditions
Thermostat met
Fire takes long time to idle down, causing overheat
Outfire due to timer skippage

Any of you who've seen my posts know I want my AA to replace my KA6 in the worst way, this is partially why...the KA6 takes FOREVER to get a good fire going...and then it overheats on idle.
I read in this thread: Storage Tanks
about running the thermostat of the LOW limit? So questions:

1. Is this a diff setting that I should be fiddling with (currently 10)
2. Is exhaust condensation really only an issue if the the entire body of water gets to 140? (or at least that near the exit area) the return line doesn't go into the stack, it goes into the boiler water!?
3. Can I wire it to run the T-T features off the low limit and not stoke unless that's violated? (run with a high differential, like 20 (just use the high limit for override purposes?) Many times I know the heat load will be satisfied quickly, the boiler is at 165 (set to 160-180) and even if the temp drops to 150, the timer throughout the day will bring that temp back up, I don't want stoking in that case!

Maybe don't answer my q's directly, but answer my folly. These shoulder months shouldn't be giving me outfires! With my current timer settings the fire will never go out and holds 150-170 with DHW usage...I'm happy with that, the T-T is just escalading things too much


These might be stupid questions....

How do you have your timer and circulator(s) wired?

Keystoker boilers are designed to have dump zones. It should not be wired to skip timer cycles. It should be wired to dump using an l4006b aquastat. The 4006b is typically wired in parallel with the thermostat of the zone you want to be your dump zone (and set at 220°). Again, a K-6 should never be wired to skip timer cycles

See page 11

Rob R. wrote: ↑

Fri. Sep. 30, 2022 2:05 pm

How do you have your timer and circulator(s) wired?

Thru the ZR , it won't run if the high limit is exceeded. I also HAVE a N/O dump zone aquastat but the plumber didn't feel it was necessary so he didn't install it. I guess maybe that's my issue. It's interesting I've checked a couple houses of friends around here and I have yet to see a dump zone or low water cutoff on any household boiler, oil or coal.

I'm not trying to re-invent the wheel but it seems like nobody else has the impatience with their unit like I do, it takes at least 30 minutes (no joke) on a heat call to raise the boiler temp even 1 degree when the fire has just idled via the timer all day.

Even with cast iron radiators and about 150 gallons of cold water in my system during the shoulder months, my Kaa-4 can go from 210 down to 140 and back up to shut off at 165 in about 20 minutes. Mine is set to burn right around 6.75 pounds per hour. What is your feed rate. I'd think a typical feed of 10 pounds per hour for your k-6 would easily keep up with the low volume of a baseboard system.

Do you have a bypass loop installed at the boiler?

Retro_Origin wrote: ↑

Fri. Sep. 30, 2022 3:43 pm

Thru the ZR , it won't run if the high limit is exceeded. I also HAVE a N/O dump zone aquastat but the plumber didn't feel it was necessary so he didn't install it. I guess maybe that's my issue. It's interesting I've checked a couple houses of friends around here and I have yet to see a dump zone or low water cutoff on any household boiler, oil or coal.

I'm not trying to re-invent the wheel but it seems like nobody else has the impatience with their unit like I do, it takes at least 30 minutes (no joke) on a heat call to raise the boiler temp even 1 degree when the fire has just idled via the timer all day.

Well at least we know the issue, you have it wired wrong. . The manual is your friend.

You need that dump zone aquastat hooked up and the timer not going through the high limit, that way you won’t skip timer cycles, and you can run a bit more aggressive on the timer to increase the responsiveness of the fire.

What is the big deal if it takes a while for the boiler to wake up?

Rob R. wrote: ↑

Fri. Sep. 30, 2022 5:51 pm

Well at least we know the issue, you have it wired wrong. .
What is the big deal if it takes a while for the boiler to wake up?

Good to know! I actually didn't fool with the existing timer wiring when I got it, since it was all tied in together and I truly knew nothing about it I just left it be. So I was guilty of omission rather than commission, I didn't wire it wrong...but I didn't check to see if it was wired right!
So I now understand that it's better to try to deal with an overshoot (dump) than try to always maintain a low temperature where heat load won't be consistent throughout the day. Got it. I up'd the timer too a tiny bit to help keep the fire fresher.

I'm not so concerned with the long wake up time, but the delayed response (too small fire at heat call and too big of a fire after heat call) is harder to manage than if it was a little more responsive, like in the winter months. At least I know what to do now!

Here's some picture so of the bypass loops, according to Dan H.'s book this is the less preferred method since it's moreso mixing incoming water with out going water rather than mixing incoming water with boiler water.

Per Keystoker's wiring diagram your timer should be connected right to B1, so it can run the stoker motor even if the boiler temperature is over the high limit setting in the triple aquastat. The older manuals called for the use of a dump zone aquastat to keep the boiler from overshooting, which is fine...but that is not enough to protect you from the timer failing on the "on" position. You should really have a second high limit control as well. One of the high limit controls with a manual reset is best. As an example, you could set your triple aquastat at 160/180, the dump zone at 210, and the manual reset high limit at 220.

As for the low water cut off, that code now and must be on all boilers. Your plumber put it on to cover his hind end. As for the over shoots, you could lower your aquastat to 140/160. You only really need 180 for the coldest days of the year. Yes I know I am opening a can of worms with that setting, but I run AA at that over the summer. Like said above just be sure that a secondary high limit will keep the boiler from running away.

ziggy87 wrote: ↑

Sun. Oct. 02, 2022 6:48 pm

As for the low water cut off, that code now and must be on all boilers. Your plumber put it on to cover his hind end. As for the over shoots, you could lower your aquastat to 140/160. You only really need 180 for the coldest days of the year. Yes I know I am opening a can of worms with that setting, but I run AA at that over the summer. Like said above just be sure that a secondary high limit will keep the boiler from running away.

The plumber did not install a LWCO
So I do use this for DHW so I suspect if I kept it at 140/160 it would probably drop too low. I hope to run at 150/170 this winter since my main floor is using radiant it shouldn't need the same temperature as the baseboards.
Doesn't the AA struggle to keep that low of a temp? To me that sounds like trying to idle a car at 25 rpm, maybe I'll just have to take a drive over to halifax...