ZR ZC and cold start

Dave M

Have a 5 zone Taco zone controller and an L7224U aquastat. ZC wired to ZC and ZR wired to ZR. L7224 is set to warm start. The circulators drop out when boiler temp goes below LL -diff and they restart again when it goes above LL just as it should. The boiler is only for for space heating, no DHW. I'd like to try it as a cold start and save some fuel but still have the circs controlled by ZC signal to the Taco. I know if I just set the L7724 Low Limit to "off" it makes a cold start but then I'd lose my LL control of the circs. I'd like to leave the L7224 in warm start but use the unused isolated relay in the Taco in series with the burner control wiring. Since the isolated relay is not energized when there's no call for heat the LL function would be defeated, the burner would not start, and the boiler would go cold. When a call for heat occurs the isolated relay closes and the burner can start and go up to HL. So I'd have a cold start but with circs that do not operate when temp is below LL. Make sense?

Joe Mattiello

There are 2 wiring schematics available when using the Taco SR. The one more commonly used is the traditional cold-start, XX to TT terminals on the boiler.

When using a triple aqua-stat as you mentioned, to prioritize the tank-less coil ZC/ZR terminals are wired with min 14 gauge wires to corresponding ZC/ZR terminals on the L8124 relay.

This works well when we want to disengage 120 volts to the relays, to temporarily interrupt the heat zones while the boiler is trying to keep up with the domestic load.

If you want to convert the boiler to cold-start to save energy, keep it simple, and use the cold-start wiring schematic XX to corresponding TT on the boiler relay. now you can drop the temperature to cold-start without any interuptions on power to the circulators. Incidentally, you can always use the coldstart wiring method, but you lose the opportunity to prioritize DHW.

Unless I'm mistaken, I am only human, you will not benefit by using the alternative wiring ZC/ZR terminals when running the boiler as cold-start. Hopefully this was helpful, and satisfied your query.

Dave M

I do know I can connect XX to TT for total cold start but I want to take advantage of controlling the circs and keeping the boiler temp up. It's a low mass boiler and as soon as the circulators start it drops the water temp below low limit and into condensation. Right now the circulators shut off briefly, about three times, before the temp in the loop is warm enough and then the pumps stay on until the call is satisfied. That all works good.
When this system is operated as total cold start it builds up a lot of cooked on deposits that make cleaning very difficult. As one might expect. I'd like to cold start the boiler up to LL and then start the circs to minimize the time it fires in condensation. It'll keep it lots cleaner. But I don't need to keep it warm ALL the time. Since it's low mass it heats from room temp to LL in 5 minutes.

Eric_32

Joe... question for you. Do the pumps receive power from the ZR/ZC terminals or do they receive power from L1 and L2?

In other words... does the load of the pumps go thru ZR/ZC terminals, or.. does ZR/ZC pull in a relay and the load is from L1 and L2?

We have a thread going on in Controls Forum and that was brought up.

Thanks!!
Eric

Dave M

I would think ZC pulls in a relay and the load is from L1/L2. ZC is a signal to the Taco that the temp is up and it's OK to run the pumps. Otherwise you'd be driving the pumps with current from the acquastat. I'll be interested to hear what Joe says.

Dave M

So I guess what I need to know is if the isolated relay on the Taco is rated to carry the current to the burner circuit. Instead of connecting B1 from the acquastat directly to the burner I'd run to the isolated relay and back so that the burner doesn't run unless there's a call for heat and the isolated relay closes. And just wondering if anyone has done this. It seems a good compromise to save fuel and still maintain circ control and minimize condensation. Btw, no cast iron radiation, all fin tube.

Eric_32

If you want to make your boiler aquastat relay a cold start, you have to disable the lo limit.
To do that......

Shut off power to the boiler,
remove the white wire out of the (differental knob (should be white) from the front.....

Remove the wire out of the lo limit knob (most likely Red) from the front.....

To remove these wires... stick a very skinny screwdriver or finish nail in the opening on the side of the wire while pulling on the wire at the same time, it should release easily.

use a wire nut and join these two wires together, there is no more lo limit control. The boiler will only run during a call for heat.

billtwocase

I know you are trying to save a few $$ on oil, but what boiler do you have? Not all are cold start friendly. As Ice would say, you are going to step over a dollar to pick up a dime, or something like that. I also agree with that statement. I see what cold start can do

Dave M

The aquastat is an L7224. I know how to make that a cold start. Just set the LL to off. I'm looking for a more sophisticated setup to retain ZC control of the Taco and circs but fool the system to go cold when there's no heat call. I think I can do that by leveraging the unused isolated relay and using it in series with the B1 burner wiring.

billtwocase

what about jumping "T-T" in the aquastat, run "T-T" from the panel relay to The cad cell control, leave the LO limit set about 120? Just thinking here for a min

billtwocase

I think you can drop Z-C at that point?

billtwocase

nah, scrap that idea. You are not using C-1 in the aquastat

billtwocase

From control pic above, it is the blue wire you want to remove to make it a cold start, but C-1 will continue to get power when the LO temp setting is reached

STEVEusaPA

How bout a little old school approach? Change the control to cold start. Get a strap on aquastat and wire the the circulator in series from C1 thru the strap on aquastat to the circulator. Then the circ will only work when the temperature is up to the preset temp, during a call for heat, & the boiler won't maintain temperature.

Eric_32

I think that may be the easiest approach to doing what Dave is looking for. Doesn't seem possible to do with just the aquastat relay alone. But with a multi box there are multiple pumps involved. I think the strap on or probe type add on aquastat would have to interrupt ZC on the Taco box still. That would let the boiler go cold when no tstat call.

Dave M

Hi Eric, yes, exactly, I was thinking the same thing about using a strap-on to interrupt the ZC to the Taco controller. And that would work. Then I got to thinking that the ZC control between the aquastat and Taco controller is already there and doing what it's supposed to and working fine. And why lot leverage that instead of adding another sensor. That's when I thought with two more conductors I could use the isloated relay in series with the B1 wiring and prevent the burner from firing unless there's a call for heat. I've already pulled a pair of #14 stranded in new flex conduit and I'll try it this weekend. In hindsight I probably should have posted in the controls section but I didn't know there was one until someone mentioned it here. Cheers.

icesailor

The easiest approach would be to set the "Hi" setting to 160 degrees and leave the "Lo" where you have it at 140 degrees. The house is probably over radiated anyway and you will save far more money with the lower "High Limit" than you ever will by turning the boiler into a cold start.

In MY minority opinion, you will burn far more fuel trying to warm up the boiler while the combustion efficiency is crap, than you will ever save. I personally think it is a net loss to you.

One of the major anti-pollution devices on automobiles is EGR (Exhaust Gas Recycling) which runs hot exhaust back under the fuel injection/air entry for a hotter air fuel mixture and better fuel burning. When the engine is cold.

Why does the instructions for my Digital Analyzer say to do the testing once the boiler is hot?

Try doing a test when a cold start first fires off and cold water is flowing into the bottom chilling the bottom of the flame.

With higher pump pressures. you get higher fuel pressures as the fuel goes through the nozzle, from the heat of compression. Once the high pressure drops, the fuel is cold. Then, it is harder to burn efficiently when the boiler is cold. Especially the cold bottom of chamber less boilers.

Or take a multi-zone cold start system. Turn on one zone and get it hot. Test it and get it efficient. Turn on the rest of the cold zones and test it again. The numbers will go way down when the boiler gets cold. Guaranteed.

They always did for me. Maybe they don't for everyone else.

Dave M

Hi Icesailor...actually this particular house is under radiated. The circulators run forever and can't keep up. If I live long enough I'll add some baseboard!
I'm with you generally on cold start. And this particular small cast iron triple pass boiler is almost impossible to clean after one season. It takes almost all day to get it right.
Now that I have observed this boiler this fall as a warm start, when there's no call for heat it fires about every two hours and runs for only two to three minutes. I'm weighing which is best. Fire a dozen times a day for three minutes. Or fire only when there's a heat call and run for seven to ten minutes before turning on the circulators. It doesn't seem like all those short cycles would be good. I know, everything's a compromise!