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UBoiler 11-06-2007 09:08 PM

utica boiler ignites for 5 sec. then shuts off
Hello. I have a Utica boiler model MGB 100 HID with a Honeywell s8600m auto igniter. The thermostat signals boiler to heat, electric vent damper opens, igniter sparks and burner lights, Taco circulator pump runs, and everything seems fine for approximately 60 seconds, then burner shuts off. Pump continues running and the vent damper closes. The igniter will spark again and light the burner for maybe 5 seconds then shut off {the vent damper continues 2 open and close as it should}. Pump continues running; however its moving cold water. I replaced batteries in the thermostat. I do not see a thermocouple on this model. I am shutting down the gas and electrical on this system and am thoroughly cleaning and checking the boiler flueways per the user's manual. I replaced the standing pilot cartridge and would appreciate some step by step trouble shooting. From the wiring diagram I am considering a lot of possibilities and I prefer a more calculated step by step approach. Please help. Thanks Cliff

skymaster 11-06-2007 09:42 PM

If it has a cad cell like oil burners I would start right there.

UBoiler 11-07-2007 10:37 PM

Thanks for the CAD idea but I'm seeing anything with those initials on the MGB boiler wiring diagrams and component coding so I'm guessing it doesn't apply to this natural gas boiler. What does CAD mean or do? Tonight I cleaned the boiler flueways and made sure motorized damper opens and closes properly. Near the bottom of the combustion chamber is a roll out safety switch and at the low end of the external venting is a blocked vent safety switch. These each appeared practically new and clean and venting appears to be all right. Anyone out there familiar with the likelihood that either of these are tripping my boiler off? Tomorrow afternoon I'll mirror up my chimney liner to be sure I haven't a blockage ie bee hive or squirrel nest. If anyone has any ideas how to trouble shoot each possible culprit or at least an order of attack I would very much appreciate it. Thanks again. Cliff

skymaster 11-08-2007 10:47 AM

Cad cell is by any other name a FLAME SENSOR .If a heater has controls that would be working normally, there is a flame sensor in the burner unit. If when a burner ignites and the sensor does NOT "see" a fire it shuts it off in safety mode. When your boiler shuts off do you have to push the RESET button to get it to refire? IF so then the problem probably is in the control unit itself or the flame sensor

vrivera21 11-09-2007 07:13 AM

I had similar problem but with a Goodman furnace. Seems the tube that connects to the pressure switch had an obstruction inside. It did not allow the sensor to work properly. After "blowing out" and cleaning the inside of the tube the system kicked in and stayed on. Go figure.

UBoiler 11-09-2007 11:10 PM

Thanks for the input. Boiler's working fine today. I think cleaning the 2 sensors did it. If I were 2 shade-tree mechanic advise trouble-shooting

1. look 4 obvious ie water on floor, breaker tripped, gas bill unpaid, stove not working
2. check thermostat, replace its batteries
3. using the manual thoroughly clean and prep for heating season
4. using the wiring schematic find possible safety switches that could trip and determine if there is a SAFETY reason boiler shuts down.
5. Reader's Digest New Home Repair Manual indicated that thermocouple failure was likely. $15 part that is the ignitor/thermocuple? and gas orifice. I replaced.
I believe the blocked vent safety switch was my problem. I dusted it off and disconnected and re-attatched its leads. I also checked to be sure I didn't have a blocked liner, vent, or not functioning auto-damper. Thanks Cliff

UBoiler 11-13-2007 08:46 PM

Well it is back to running as I originally posted: ignites and runs for a minute and then trips off, then it recycles and fires back up for another 2-5 seconds and then trips off.

I looked at the books at local bookstore but all were basic and unhelpful. I looked at vo-tech bookstore to see what they had. Does anyone have a troubleshooting HVAC book they think I should track down? Thanks. Cliff

#CARRIERMAN 11-14-2007 05:56 PM

Hi UBoiler

It sounds as though your boiler is new enough to have electronic ignition. However I will need some specific information to make this determination. I read where you said you replaced the pilot, did it have a small diameter wire on one side and a larger diameter orange wire on it. Did the wires plug into a box? If you could give me a little more information or post a picture. I can give you the solution to your problem. It is at this point sounding like you have an ignition module problem which could be caused by a corroded ground. Be glad to help you if you can give me more to work with.


UBoiler 11-14-2007 08:42 PM

More info
Hello Rusty,
Great to hear from you. The identical part I replaced was Standing Pilot Cartridge For MGB. It has an orange wire{ looks like spark plug wire} that connects into position #9 -Spark on the Honeywell S8600M Continuous Re-Try 100% Shutoff IP 90 second trial for ignition Auto Ignitor. The other wire from the Standing Pilot Cartridge {looks like fatter more robust thermocouple wire} connects {looks like attaches with a compression nut} to a Honeywell natural gas valve VR8204H 1006 Reg 3.5 ADJ. The auto igniter has four wires numbered labelled colored as such: 1. MV-red 2. MV/PV-white 3. PV-blue 4. GND[Burner]-green and the first 3 wires combine into a plug and plug into the gas valve and the green plugs separately into the valve. The auto ignitor has two additional wires 5. 24V[GND]-black and 6. 24V-black and these travel to the blocked vent safety switch and the roll-out safety switch [looks like connected in a series]. The 6. 24V originates from the Aquastat Relay Type L8148E box. Hopefully this lays it out. Thanks Rusty. Cliff

UBoiler 11-18-2007 10:56 AM

I still haven't repaired my boiler problem. I'm burning a lot of wood to keep my house warm but we'll be out of state over Thanksgiving so I have to fix this in the next couple days. I hate to just buy new parts and replace but using the info I've provided if any one would give me your best guess what you would suspect/check/replace first then second and so forth I'd really appreciate it.

I'm guessing this order suspect/check/replace
1. all my wires and connections
2. I have a new Lux thermostat and batteries so I'll just re-check.3. already replaced gas nozzle and igniter (standing pilot cartridge)
4. roll out safety switch
5. blocked vent safety switch
6. Honeywell auto igniter box
7. aquastat relay box
8. Honeywell gas valve

Please send me your ideas or order changes or anything that you see I haven't considered. I could really use the input. Thanks and good luck. Cliff 11-18-2007 02:01 PM

Wiring diagram
Cliff, If you email a picture or copy of the wiring diagram to I will see if I can help you.

UBoiler 11-19-2007 09:32 AM

Good morning. I checked my wiring visually and cleaned connections, re-connected. I replaced the roll-out safety switch and the blocked damper safety switch. I replaced Honeywell auto igniter module with the Honeywell replacement module S8610U Universal Intermittent Pilot Gas Ignition Control. This new design has the LEDs flashing yellow and green with an installation / trouble-shooting pamphlet. The LEDs have so far only given me heart beat normal operation and normal fast flash at start up. I gotta get out and make some money so I'll check in tonight and report status. Again if anyone has some info out there I'll take it. Good luck and thanks. Cliff

UBoiler 11-19-2007 10:32 PM

Well, nothing changes unless something changes. My buddy at work asked me 3 weeks ago why don't I just have a guy come out and fix the boiler? I really like knowing how and why things work, and unfortunately I'm one of those learners that has to do to learn. Also I know in the trades it can be annoying running into the last stop of the day and the guy wants to talk when we just want be home enjoying left over turkey noodle soup and we've been looking forward to that hot, flavorful broth since cold sandwich lunch.

Found an old book that showed jumping the aquastat as a way to determine if the failing or undiagnosed problem originated there. Didn't successfully jump it. Suspect another safety feature or my own poor execution.

Looks like temps while we're gone to be in the 20's to upper 40's. We'll only be 16 hrs away so if disaster strikes we'll be a bathroom stop away. Thanks and good luck. Cliff

MGB150HID 11-20-2007 08:43 PM

Similar Issue
I have a similar isssue I have a MGB150HID. My pilot light will stay light but the unit will not fire up! I have cleaned and checked averything out and I am not able to locate why this darn thing will not fire up; it's getting really cold out.... While cleaning I either disconnected the #4 GRN (Burner) wire or just moved it relaizing that it was disconnect from near the pilot light. Never the less the unit will still not fire up! Can anyone please plese UBoiler and myself. If anyone wants to see some pictures I have them. Shoot me an email and I will send them to you. Thanks!! JARED

UBoiler 11-23-2007 07:24 PM

Hope you all had a great Thanksgiving!!

Here's what I Band-Aided for while out of town:

The front of the aquastat has two electrical leads , top has a torx screw and the bottom has a torx that's made to be not easily removed (has outward dimple in center of torx ). I removed the top lead and when it made contact with the metal aquastat case boiler fired up. I discovered the boiler working apparently fine in this configuration; the thermostat controlling the boiler's cycling. The aquastat/transformer share same box called the aquastat relay. The auto damper does not work in this current configuration; the auto damper is controlled from the aquastat relay box. I replaced auto damper with open flue line. The newly installed auto igniter module box is capable of controlling the auto damper.

I intend to replace aquastat. I'll see how that goes. Any thoughts?? Thanks and good luck. Cliff

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