Please Help w/ Boiler Wiring Diagram!


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Old 10-21-07, 07:28 PM
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Please Help w/ Boiler Wiring Diagram!

Hello All,

Background:
I'm trying to troubleshoot my boiler (a mid-90s Buderus G124X II), which stopped working for no known reason. In my troubleshooting, I ended up burning up the Aquastat transformer. Since I'm going to replace the entire HVAC system in the spring, I'm trying to put on a bandaid until then (instead of replacing the entire Aquastat, which I'm not sure is necessary anyway). I bypassed the existing 24V AC transformer and found one at Radio Shack that's 25.2V AC (27.0V w/no load) - first of all, is that a problem? Amperage it can handle is within a few milliamps of what the Aquastat specs say it uses (800mA).

Wiring Problem:
Anyway, on to the troubleshooting.. Here are two wiring diagrams for this boiler:
Physical Diagram and Logical Diagram

In the logical diagram, I get 27V from Z <-> 24V GND (as expected), but only 3.6V from the "B" (top) side of the "TR High Limit" sensor <-> 24V GND. So it seems that "K1" is what's dropping the voltage, and thus my question - what is "K1"?

Do I really need to replace the entire Aquastat?

Thanks for any help you can provide! It's much appreciated - I look forward to quite a bit of interaction on this forum, on both sides (helping out and being helped).

-Tim
 
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Old 10-21-07, 09:15 PM
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Honeywell uses the designation "K" for relays. K1 is the relay that is controlled by the thermostat.

On a call for heat the coil of K1 is energized and it closes a set of contacts to start the circulator. A second set of contacts closes from Z to the limit switch chain. As long as the limit switches are in the closed position the spark ignition module is energized and the burner is ignited.

Are you making your voltage measurements with the thermostat in the "heat on" position AND waiting until the vent damper is fully open?

Furthermore, the correct measurement points would be B2 to B to check that the K1 contacts have close, B2 to R to check that the high limit is closed, B2 to B1 to check that the vent damper is open, B2 to 2 to check that the flame rollout switch is closed and B2 to 1 to check that the blocked vent switch is closed.


Understand that replacing the transformer voids any UL listing on the Honeywell control. It is also possible that the Radio Shack transformer does not have sufficient output wattage (amperage) to operate the control.
 
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Old 10-21-07, 09:42 PM
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Thanks for the response, furd.

Based on your response, I'm a bit confused as to how the symptoms of my problem could be occuring. First of all, another bit of information I omitted before - when I first added the "new" RS transformer and turned the power on, the damper went from open (has been that way since it broke) to closed.

I have both thermostats calling for heat. When I turn the power on, there's a few second delay, then the circulator turns on and keeps running indefinitely. The damper doesn't open, and the burner doesn't light.

So now I suspect that the damper doesn't come on since the K1 relay isn't closed and it's first in the chain. The circulator comes on since it's on the line (120V) voltage side, but if the K1 relay is the same thing for both line and low voltage (there's a K1 on each side of the diagram), then why would it close on the line side and not the low voltage side? Perhaps it's directly related to not enough amperage from the transformer? Or could it be another issue? (I would like to rule out everything except the transformer itself first)

I understand the implications of voiding the UL listing on the Honeywell aquastat (insurance issues, etc). At the moment I'm really trying to just get it working so I know what the issue is, then perhaps swap out the Aquastat later.

Thanks again!
 
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Old 10-21-07, 09:59 PM
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Honeywell uses (in my opinion) cheapo relays so the failure of one set of contacts is not out of the ordinary.

Try jumpering from T to W (around the second set of contacts on K1) and see if the vent damper opens on a call for heat.

Also check all the limit switches.
 
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Old 10-22-07, 10:15 AM
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I'm a bit confused as to why I would jumper T & W. Don't they just provide the power for the K1 relay? The reason I ask is in the diagram, if the thermostat(s) call for heat, they're closed, and if I jumper T & W, that will close the circuit with no resistance (arc it). Out of curiosity, I tried that, and nothing happened (incl. no circulator this time) except a slight burning smell (from the transformer, I think).

I removed the jumper and the circulator worked again, but no damper. By the way, the brown and black wires on the damper are getting the correct voltages (27V differential).
 
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Old 10-22-07, 11:06 AM
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I'm sorry, you are correct about T and W. I meant to write jump between B and W (or B and Z). This would bypass the second set of contacts on relay K1.

Connect one end of your meter to TV (or B2) and with the thermostat calling for heat and the vent damper fully open check for 24 volts at B, R, B1, 2 and 1. Most likely one of the limit switches is not closing.

If you have 24 volts all the way to the S8600H ignition module then the module is the problem.
 
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Old 10-22-07, 04:48 PM
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No problem - I jumped B & W, set thermostats to call for heat, then turned on power - the damper opened. Once the damper opened completely, the circulator turned on and the device on the middle right of the Aquastat (looks like a contact relay with a coil on half of it) started clicking, with minor sparks as it contacted.

It did that repeatedly until I shut off the power (probably waited 10 secs or so). The burner didn't come on, and I didn't wait long enough to really test the limiters, but will maybe do that after I get back home in an hour or so.

I did quickly check the 24V <-> 24V GND and it said 0.03V. Not a good sign, but I'm not sure why that relay is continuously clicking.. Will be back for more troubleshooting in an hour.. thanks again for your help!
 
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Old 10-23-07, 06:19 AM
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Looking at your schematics, and considering furd's advice, I don't understand why the circulator waited until the damper was closed before it started. The circ should start once power is applied and t'stat calls for heat.

The thing with the coil in the middle center of the aquastat is K1 . If that relay is chattering, it's a very good sign that your cheapo toy RS transformer isn't up to the task of running the control. If you must persist in your line of troubleshooting, you would be better advised to pick up a 24VAC control transformer from HD or Lowe's, or a plumbing/heating supply.

What you should see as a sequence of operation when you have B and W (or Z) jumpered is:

Apply power

Damper should open immediately (because you have B and W jumpered, the controls think there is a call for heat already)

NOTE! with B and W jumpered, burner may start now! because you are BYPASSING the thermostat control of same with your jumper.

If burner does _not_ operate at this point, the problem is either:
the toy transformer can't supply enough power to operate the controls,
there is a loose or otherwise defective connection in the wiring,
the limit switch in the aquastat is either defective or satisfied that the boiler is hot (open),
the damper proving switch in the damper is either defective or otherwise open,
the rollout switch is defective or otherwise open,
the blocked vent switch is either defective or otherwise open,
the gas valve is defective.


Call for heat from t'stat

K1 should pull in (and not chatter)

Circ should run only after K1 pulls in
 
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Old 10-23-07, 12:06 PM
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oops...

above I wrote:

"...don't understand why the circulator waited until the damper was closed before it started..."

I meant OPEN .
 
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Old 10-23-07, 12:20 PM
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Thanks for the info, NJ Trooper.. it's much appreciated.

I think the "new" transformer is too weak as well. The damper opens much slower than normal, which obviously indicates a lack of juice. I'll look for another one as I'll be shopping around tonight anyway for cabinets & tile. I can't say I've ever seen one at HD, though I haven't really looked specifically.

I'm not 100% positive that it waited for the damper to be open, but I didn't notice it come on while it was opening (which, as I said, was slow). Perhaps there's a switch between orange and yellow for the damper that doesn't close until it's open. That would make sense from a safety standpoint (not to turn on the burner). Obviously the circulator is unrelated to needing the damper open, but isn't the circulator on the same time as the burner? (when there's a call for heat)

Thanks again.. I hope I can find a transformer, otherwise I'll have to search for an HVAC supplier.
 
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Old 10-23-07, 12:39 PM
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Yes, there is a safety (limit) switch in the damper motor that requires the damper to be fully open before the burner will fire. That is represented by pins 3 and 4 of the damper assembly on the logic diagram.

The circulator is controlled by one set of normally open contacts on relay K1. A second set of contacts on relay K1 closes the 24 volt circuit to operate the burner.

Note, I do NOT recommend that you jury-rig a new transformer on your control but if you must, it is fine to get a 24 volt transformer with a much higher VA rating than necessary. Too low a VA rating will cause trouble (not work) but higher will cause no trouble.
 
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Old 10-23-07, 12:41 PM
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If it is indeed wired as the schematic shows, as soon as K1 pulls in, the circuit is completed for the circulator to run.

The 'square thing' in the schematic labeled K1 is the coil of the relay. The other two K1 items are two seperate 'switch contacts' that close at the same time when you activate K1 by presenting a call for heat from the thermostat.

So, the circ 'should' run as soon as K1 pulls in.

Not all HD's carry the same stock, so yours may not have them. But look around for their heating supply section and if yer lucky they will. A 24VAC 40VA transformer should be more than adequate to run that stuff.

Yes, there definitely IS a switch on the damper controls that acts as you said, to prevent burner firing into a closed damper. Usually called a 'proving switch'.

What you need to do is follow that chain down on the right side of the schematic, testing each item in that chain. Ultimately as furd sed, you need to have 24VAC arrive at the gas valve for it to do it's thing. Any ONE of the items in my list will prevent that from happening. Where it gets tricky is when TWO items go at the same time! Doesn't happen often, but it is possible.

If yer into 'logic', that string of switches works the same way as an AND GATE . They've all gotta be true for the burner to fire.
 

Last edited by NJT; 10-23-07 at 12:45 PM. Reason: heh heh, furd beat me!
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Old 10-23-07, 12:51 PM
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Originally Posted by miltimj
...isn't the circulator on the same time as the burner? (when there's a call for heat)...
Yes, but the reverse is not true. The circluator CAN be on without the burner.
 
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Old 10-24-07, 03:47 PM
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Okay, here goes..

I bought a 40VA transformer from a heating supply company and hooked it up. The circulator came on as normal, but not the damper. Once I jumped B & W, the damper turned but kept going, not stopping in the open position. The valve controls seemed to be operating, but the burner didn't attempt to fire up.

I was able to test that there was voltage getting through to the orange wire on the damper, but nothing (0.0V) to the yellow. I waited until the damper was in the open position, then flipped the switch on it from auto to manual (and it stopped in the open position, of course). At that point I heard the lower zone valve humming and was checking it out when the new transformer popped and burned out (no voltage on the secondary now).

Well that was fun while it lasted.. I'm afraid that if I put in a new Aquastat that will burn out as well. Just when I thought I was getting this.. Again, thanks for the help - looks like I'm waiting for the Aquastat to arrive now.

-Tim
 
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Old 10-24-07, 05:01 PM
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Tim, sumpin else is wrong... yes, the aquastat has a bad xfmr, but something down the line took that transformer out. I gotta go out for a bit, but lemmee think this over a little more.

Your multimeter, does it have an ohms scale ? Do you know how to check resistances ?
 
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Old 10-24-07, 05:35 PM
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Sounds good - yes, it has an ohm meter - I haven't gotten it to work quite right, but I have another one that works well.
 
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Old 10-24-07, 06:20 PM
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What are the zone valves wired to ?

If nothing is happening on the burner side of the circuit until you jumper B and W, that's telling me that that side of K1 is 'fried'. So, you are probably going to have to replace the aquastat anyway.

_Something_ drew enough current to take out the relay contacts and the transformer. And _something_ is still drawing enough current to take out the new transformer.

Since the damper didn't stop turning, and you never got voltage to the other side of the damper proving switch, my bet is that there's a problem with the damper.

But how to check it out... that's the question ... and I don't have an answer for that. Grady ? furd ? Ken ?
 
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Old 10-24-07, 07:45 PM
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I'm basically set on replacing the Aquastat, so that's fine. I just don't want to replace it twice..

Interestingly, at one point toward the very end (before it fried the transformer), I was testing something.. 24V GND to something else I think, which was just fine at 26.5V a few minutes previous, but then started going all the way to 120 sporadically on and off. I'm trying to think if it could be that the multimeter probe scraped against a line level contact, but there aren't any line level contacts at the top of the aquastat where I was. Anyway..

Edit: Forgot about your zone valve question - I'll check it out and report back.
 
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Old 10-24-07, 08:20 PM
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It's also possible that at the point just before the transformer opened up, that the primary shorted to the secondary, feeding 120 VAC to the other components.

Maybe it fried the damper controller by feeding 120 to it, and that's why it now isn't stopping at the open position.

It sounds to me as though there's a short to ground on the 24 volt secondary side of the transformer, pulling heavy current, burning that set of k1 contacts, and ultimately trashing the original transformer (and the others?). It may also be responsible for what appears to be a defective proving switch in the damper.

Disconnect the wire to the 24 V side of the gas valve and measure the resistance there to ground.
 
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Old 10-27-07, 10:02 AM
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Okay, I'm back on it. We're gutting our kitchen and had to order cabinets, etc, so we can get them here and install them by Thanksgiving..

The good news is the new Aquastat arrived yesterday, so I am going to try installing that but first test some of the resistances as you mentioned, NJ Trooper. I'm not sure I completely follow the 24V to ground resistance testing, but I'll see what I can figure out.

Thanks again! I'll give an update if something changes..
 
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Old 10-27-07, 12:16 PM
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Update:

I installed the new Aquastat, so the hacked transformer solution out of the picture for now (hopefully permanently).

The new Aquastat has a jumper where the damper connected (I have it manually set to open - ensured it is physically open, etc). It says to remove jumper and connect the damper if using an automatic damper - I'm inclined to leave it the way it is. More on this later..

What happens:
1) No call for heat from thermostats, turn on gas control knob and power
- Circulator never comes on (expected)
- 24V GND <-> Z = 24.5V
- 24V GND <-> Damper Orange = 0.4V
2) I call for heat on the lower level thermostat
- Lower zone valve opens, then circulator turns on
- 24V GND <-> Damper Orange = 24.3V
- 24V GND <-> B1 (right after damper in schematic sequence) = 0.0V

If I try jumpering around the damper, the K1 relay clicks frantically, so I immediately stopped.

As for the damper jumper, strangely, it's a harness that only jumps two wires - the yellow and black pins (I can tell based on the damper harness wiring). But the pins with voltage on them are brown and orange. So it seems the damper block with orange/black/yellow/brown in the logical diagram doesn't connect the way we think it does (i.e. orange to yellow - unless I'm missing something). If it does, then why is the relay clicking like crazy?
 
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Old 10-27-07, 12:36 PM
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What is the exact model of the damper assembly ?

What is the exact model of the aquastat ?

That relay is chattering because for some reason the transformer in the aquastat is being shorted out when you put that jumper in place. Relay K1 is closed, with the jumper in, it's shorted to ground, the voltage 'goes away' because its shorted, the relay opens, the voltage comes back, the relay closes, repeat ad infinitum.

No, there's something wrong here, either the schematic you posted is wrong, or the damper controller is fried, or there is some slight differences in the wiring between the old a'stat and the new, or there is a short in the wiring to the roll out switch or the blocked vent switch, or the gas valve is defective.

By GROUND, I'm referring to the 24VGND (or B2 or TV, they are all electrically the same point). Put one probe of your multimeter set to ohms scale on there. The other probe will go to the the 24V on the gas valve (or 1 or ORANGE wire, again, electrically the same point). I'm not sure what the reading should be exactly, but I am sure that you don't want to see a SHORT ( ZERO OHMS ). Do this test with power OFF, and the plug to the damper disconnected. It should "probably" be above 20 ohms or so, I would think even higher, maybe 50 - 100 ohms even... (Grady, furd, Ken, any data on this?)

Check yer PM's ...
 
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Old 10-27-07, 12:44 PM
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Aquastat: Honeywell L8148E1265 (new one.. I can't find anything past "L8148E" on the old one)

Damper: Effikal RVGP-KS5-BKF (24VAC, 80ma)
 
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Old 11-02-07, 06:59 PM
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Thumbs up

First of all, thanks a TON to NJ Trooper for all of his help far above and beyond the call of duty to help me figure this out! You're truly a great man.

The problem ended up being a vent sensor proving switch being shorted out to ground by touching a pipe that was very close to the vent stack.. <sigh>

But it's fixed now - just working on getting the pressure stabilized and air out.. (I can't find any bleed valves on any radiators).

So thanks again, NJ Trooper for your amazing assistance!

-Tim
 
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Old 11-02-07, 08:24 PM
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You are much more than welcome miltimj ! It's the least I can do to do my part to repay you for what you've done for ALL AMERICANS! THANK YOU!

For folks reading this forum,... there was a LOT of 'behind the scenes' work y'all didn't see on this one !
 
 

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