How is a boiler suppose to work?


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Old 12-20-08, 10:39 PM
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How is a boiler suppose to work?

Hello,
I have an apartment building with 7 units, one zone for each unit. The boiler has a high limit and the L6006a low limit / circ control. My tenants were complaining that the heat was inadequate so I started to look at the system and how it was wired.
Whoever installed it years ago switched the thermostat power threw the L6006a. This caused the zone valves to only be powered when the water temperature dropped below the low limit setting. Basically it would sit doing nothing until enough heat bled out of the system to fall below the 140 setting, at that point the boiler would fire and the circ pump would run. It would run until the heat level (from the somewhere) was reached and everything would shut down again. I rewired the auqastat, then it would run the pump until the burner kicked on, at that point the pump would stop. That seems dumb to me since it was only heating the water in the boiler itself and whatever water circulted out because of the heat.
Tonight I wired the circ pump to the zone valves so it runs anytime their is a call for heat. So now I am trying to figure out how to get the burner to stay on... The high limit seems to want to fire the boiler anytime it is under 10 degrees from the high limit. I wired it threw the L6006a so it comes on when the water temperature drops to the setting minus the differential. The problem is once the temperature rises to the differential plus the set temperature it shuts off.
I can't seem to find any way to have the boiler fire at say140 and shut off at say 190. I seem to have only two options. Either have it fire at 180 and shut off at 200 if I use the high limit to control it, or have it fire at 125 and shut off at 155 if I use the low limit?!? Does anyone know if I completely screwed up this wiring somehow or maybe I am asking the impossible?
 
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Old 12-21-08, 09:20 AM
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OK, I would imagine that there is a controller for the circulator. That is triggered when any of the zone valves are open. Does this controller have another set of contacts in it? Better yet would be to post back with the name & model # of this controller.

Then look at the burner controller. There should be a set of TT terminals on it. See if they are jumpered. Most likely are, which would cause the burner to run the way it does.

What needs to be done is to open the TT terminals on the burner controller. Then use another set of relay contacts to close the TT terminals when a zone calls for heat.

Note: DO NOT apply 120V to the TT terminals. They only get a contact closure such as a set of relay contacts or a two-wire thermostat.

The L6006A will stay in place as the high limit cutout for the burner power. You just want to change the burner control so that it knows when a call for heat is coming in.

There is one instance where this will be different. That would be if the burner has an oil valve and uses post-purge. To retain the post-purge the wiring gets a little more complicated.

Post back with the model # of the circulator control along with the burner primary control.

Al.
 
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Old 12-21-08, 11:28 AM
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Hopefully I can explain this.

The high limit is a Honeywell L8148A So what I have is the T and TV connected to the zone vales, W and Z tied together on the L6006A at W, I removed the wire that was connected to the burner control B and replaced it with a connection from the B on the L6006A. So what I am thinking happens is, when the zones call for heat it energizes Z which then feeds power to W starting the pump, and when the temperature drops it makes W and R which sends power to B which then makes B and R and causes the boiler to fire. The problem with all of this is that the L6006a breaks W B after the differential is reached. If I had left the original wire connected to B and not run it threw the low limit it would fire at the high limit differential... Also this is a gas boiler with no dhw. Thanks
 
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Old 12-21-08, 12:09 PM
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OK, forget what I posted above as I was thinking oil burner.

For the L8184, only the 'E' model shows W & Z terminals. Download this pdf (it covers both A & E models):

http://customer.honeywell.com/Techli...0s/60-2278.pdf

Note Fig. 8, that is most likely how it should be wired. It looks like having the L6006 in the mix is messing it up. I don't see the need for it in a multi-zone system.

Al.
 
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Old 12-21-08, 01:27 PM
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It is the E model I tired wiring the way figure 8 shows. Then when the temperature was set to 190 the burner would come on at 180 and go off at 200. I would like to be able to use the stored heat down to about 150 or so before the burner comes back on... I also tried wiring the way that figure 7 shows and that is when the pump would only come on while the burner was off. One note is that I removed the jumper between W and Z and directly connected the two on the L6006a on W. In looking over the installation manual for the L6006a it says that it is designed to not operate the pump while the burner is on. What I am trying to get is a burner that is turned on by the low limit and turned off by the high limit. I seem to only be able to have one or the other in use at a time?
 
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Old 12-21-08, 02:49 PM
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The Fig. 8 operation is typical for boilers. Although there are two changes that I know have to change this behavior.

First is to use an outdoor reset such as the TekMar 256.

The other is to use a control such as the Beckett HeatManager or Intellidyne HW+.

Al.
 
 

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