LWCO issue on new install

4Barrel

Hi All-



Today i was testing the LWCO (McDonnel & Miller probe type model PS-802) on my new boiler (Dunkirk PVSB). To test it, i brought the boiler up to steam, and allowed the water level to drop as i was venting- i removed the main vents to simulate a drop in return water level). The water level dropped until the LWCO activated (at a very low level at first, but then after a few tests, it settled in). The LWCO delayed as expected, and then gave me a steady alarm, however, the burner continued to fire, regardless how low the water level became. (Note: i have a new VXT, and it feed water after the LWCO delay, but the burner was still firing).



I was pretty alarmed at this situation, so i disconnected the burner circuit, and started testing with my multimeter - i measured 24V at the LWCO terminals for both FEED and BURNER. Dunkirk tech support claims it's either - or , not both, which stands to reason. Thinking the LWCO unit is defective, I was able to quickly get a replacement unit and started the same tests. Same issue. (note - i only replaced the unit, not he probe, but the probe alarm appears to be working.)



With the new unit in place, i tried all kinds of scenarios, but the LWCO would continue to send voltage to the gas valve while the water level was too low. The only instance this stopped was when i took the T-stat out of the loop.



I don't think it's the LWCO unit - i doubt two of these are defective in the same way. it must be in the wiring. Has anyone encountered something like this, or can offer a trouble shooting process?



Thx in advance,



Jeff

nicholas bonham-carter

perplexing problem

could you compare your present wiring with a diagram from dunkirk? --nbc

4Barrel

here's the diagram

from Dunkirk - see page 14 of the manual at the link here:



http://www.ecrinternational.com/common/get_document.asp?key=397&ecr_key=4&ext=pdf



I've traced the lines, and everything appears to be wired correctly. My T-stat is connected b/t the vent damper and LWCO "hot" lead. it's prewired, so i just insert the T-stat and and vaporstat in series as shown.



i do have a question about the vaporstat connection (unrelated, I think, b/c i removed the vaporstat from the circuit, and still have the same LWCO issue - but you never know): I have L408J 1009 model that has three terminals (R, W, with "make" and "break" switching. I am wired at the R and B terminals. The Honeywell manual says the unit "breaks R-B, makes R-W on pressure rise to set point." My assumption is that this will keep the circuit completed (between R-B) until the upper limit (main) is satisfied, and then switch to the unwired terminal W, opening the circuit, when the main set point is reached. On a pressure fall, the R-B would reconnect. Do I have this wired correctly?

nicholas bonham-carter

wiring diagram

sometimes a bad ground causes some sort of backfeeding problems.

this is why it would be nice to have tell-tale lights on all the electrical components. LEDs are so inexpensive these days, and they could show more quickly where the problem was.

when we were skimming, after installing a new vaporstat, we couldn't get the burner to fire. we would have seen 30 minutes sooner  [with lights] that it was the vaporstat [mounted too low]  held open by the elevated waterline pressure. after that, we put all the gauges, and vaporstats on pigtails instead of the standard peerless arangement of a lowered manifold.--nbc

4Barrel

burner not firing

would be a better problem to have. would rather be too cold then melting down a new boiler b/c the LWCO isn't shutting the burner off ;-)



ok, so i see now that i might need to isolate the T-stat with it's own relay. going to try that.



any input on the vaporstat wiring?



thanks for your help, nbc!

4Barrel

found the issue

the T-stat was looping 24V back into the LWCO. with some great help from Dunkirk tech support, we isolated and rewired.



any input on the make/break wiring for the V-stat would be greatly appreciated!



thanks!



Jeff

Unknown

Vaporstat Wiring

Jeff- Do you have the attached  vaporstat tech bulletin?

- Rod

4Barrel

bulletin

hi rod - yes, i have this doc, and i wired the two leads to r & b as described based on my interpretation of fig 3. funny, though, when steaming today, the needle on my new low pressure dial (0-20oz) barley moved off 0. i guess i want to make sure i'm wired right n the v-stat, and then proceed to other issues. good news is the new boiler is in and working! jeff

4Barrel

found other posts

that confirmed the R-B wiring for the V-stat, which of course makes sense. still, i'm firing with the dial reading pressure below the cut out... hmmm... will do some trouble shooting and will make this a topic for another post. thanks for the replies...

Unknown

Steam Generation

I'm trying to mentally figure out your situation and am a little bit lost.  Are you sure you're making steam? Have you had your burner checked out with  instrumentation?

4Barrel

yes

i am making steam. i will post the results of my install shortly.