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Gas Boiler will not fire up for long. Works if i jump it from the relay.

Stever89 Member Posts: 2
I own a Utica MGB75HD REV5. (gas boiler, forced hot water)
2 zone house, as of right now the 2nd zone is off.
The Boiler is off, just the pilot light is on.
The thermostat is off.
I pressed in the blocked vent and roll out safety switch's.
Current temp is 61.
I turn on the thermostat and set it to 68.
The thermostat clicks showing that it is on.
The boiler temp is 120 and 20 PSI on the water.
About 30 seconds after the thermostat is turned on, the power vent kicks on.
Less then a minute later the gas valve clicks and the burner are ignited producing flame.
The relay is set to 190.
At the point the temp is up to 150 and still 20 psi.
Been running for 5 minutes and the burner tubes are no longer fired up, now just looking a pilot light. I did not see any roll out flame when it went off.
Now all that is running is the power vent and that turns off 10 minutes later.
Back at the thermostat it is still on.
The pipe where the pump is located, the return, is hot, so it is circling.
Im lost.

I turned off the gas, took out the burner tubes, cleaned them, cleaned the area around the boiler. Put it all back together, relit the pilot light. Pilot light is now on the on position and still on.
Go back to the top, of this, repeat, and back to square one, did this about 4 times since early this morning.
I changed the relay temp to 180 per some post on here. I think on one cold day the heat was not working out, think it was below 0 outside. so I put it to 190.
My relay only has one setting, no high and low like other relays.
Also now have Zone 1 off, and Zone 2 on, did the test same results as first post. After 5 minutes burner tubes go out, only a pilot light, power vent still running.

Still working on this.....tjernlund HS1 is the power venter.
So getting more into details, i have read so much more on how boilers works, i have tried a few more things to rule things out.
For starters i ran the heat on this morning for 5 hours, but i did it bypassing the thermostats.
I put a jumper in T and TV on the relay, the power vent kicks on, the Field Controls GVd-5 damper opens and it fires up. I open up the power valves.Then i have heat with no issues.

Something gets tripped somewhere so i have 2 sensors on the boiler, safety switches. i jumped those and still had issues. I jumped my thermostat itelf, still had issues. I thought maybe something is going on with the damper, so when it fired up, i have a manual switch to open the vent, and when i did that the relay was clicking and turning off the heat still.
I replaced the thermocoupler, also took out the pilot, and cleaned that with a brush, and some air, was dirty. Was able to brush out the tubes this time. Still issues, though keep in mind my pilot light never goes out.

Now for something interesting for you. I have some odd ball setup or maybe it is just code. I located a diagram and i was going to setup a test and put in new wire to the power valves but the wiring is too confusing. My thermostat goes to the valves and then the power vent and to a gas off switch, and to the relay so that is out of the question now. I have a hot water gas tank next too my burner. It is connected to the same flute that the power vent is on so it can send out the gases. Boiler and hot water are connected to a power module that trip it and tell the power vent to turn on. A few times this button or trip sensor has kicked in causing the pilot to go out on the water heater. So im just saying yes i do have some issue with the water heater, i think i relit the thing like 6 times the other day. I think when it is off, the boiler wont work so i have to watch that. thermocouple was replaced on that.
On top of all this plumber came by this week and no lie, the thing turned on and worked....he charged me 3 hours for being there. Heat all night, next morning, evening came, no heat! This was working all the right way, not jumping the thermostat.
I saw this thing where solder breaks on these old relay boards. i dont know if that is the case but i bought a new relay. thought i think i might have same problem, though i hope not. At least i did not buy the same one, i bought a replacement of mine, Hydronic relay, get a rebate from the gas company because it suppose to save me money, long warranty on it too.
Though if i can jump the relay is that telling me, the damper, power vent, the relay, thermocouple, safety switches, are all good? The in house thermostat, hits those power vents, and then the relay. So that must be where the issue is? I still have the same issue if i use one thermostat on and the other one off, and visa virsa. i have 2 zones. One power head was replaced last year because it would not open. Maybe the other one is bad? Would it trip?
Sorry for so many questions and long paragraph here.


  • BobC
    BobC Member Posts: 5,478
    I have no experience on this equipment but I worked on complex power systems for over 30 years. If there are Molex connectors used in the system be on the lookout for corroded connections, bad solder joints on board mounted connectors and the possibility of a bad crimp somewhere (those can take months to show their ugly heads).

    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
  • icesailor
    icesailor Member Posts: 7,265
    I hate it when they do that.

    Makes me want to call a Professional that might or might not know what the problem is. Then, I have to explain how it is supposed to work.

    #1: First, there is the electrical panel where the power comes from.
    #2 Everything in between:

    #3: Everything in between is just a safety switch and when everything is happy, the burner gets power and it starts.

    Not until everything is properly closed and stays closed, will the burner run. Or so it was once explained to me.

    Down to basics: How I learned to use a "Wiggy" and a Multi-meter. Then along came tick tracers. A wonderful tool. In the right hands.

    Good thing it isn't oil. All those times you tried it and the chamber would be flooded with oil. You should see what happens when it finally does fire off.
  • Tim McElwain
    Tim McElwain Member Posts: 4,622
    Give me a list of the numbers on the controls so I can get a better picture of the set up.