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Partially closed gas valve
edited December 2016 in Thermostats and Controls
Hi Guys, I have a situation where the peerless steam boiler is lit with an igniter. A call for heat will call the igniter on which instantly lights the pilot and then calls the gas valve to open. Everything seems fine. Except that after a few minutes, the flame reduces to just about a half inch over the burners and the igniter starts trying to light the already lit pilot. I was just wondering where I should start looking for the faulty component? I feel that the problem lies within the igniter control box. Either the box or the flame sensor. I'm slow to blame the gas valve or the transformer. I would love to know what you all think. I will try to attach a few pictures.
Good point Zman. I suppose that if the voltage fluctuates, it would indicate that the gas valve is responding to the different input voltages and that the problem lies elsewhere.0
That control is a Johnson Controls G60 module, I assume the gas valve is a Johnson Valve?
The system works this way on a call for heat the control receives 24 volts and internally the Pilot solenoid is energized. At the same time the spark is energized and the spark lights the pilot. The pilot proves by generating sufficient microamps back to the G60 control. That will then send 24 volts to the main valve solenoid and the spark should shut off. You want to check those points for 24 volts and check your microamps.
The microamps should be between 2 to 10 and normal is around 3 to 5. Pull the pilot and clean the flame sensor if the microamps are low. A picture of the gas valve would help.
I would also during the entire firing sequence check gas pressure on the inlet and outlet side of the gas valve. According to the rating plate the outlet pressure from the gas valve should be 3.5" W.C.1
Thanks Tim. I'll take a picture of the gas valve this evening. Just to be clear that I understand. Is it the module that energizes the pilot solenoid and then, after the pilot proves, the main solenoid? And is it at those points on the module that I need to check for 24 volts?0
Yes the gas valve is energized from the module. Check to make sure the module is putting out 24 from PV and MV terminals and then make sure you have 24 at the valve for both. If the voltage drops off at any time then go back to the transformer and see if it drops off at the transformer. If it does then stop the call for heat and check the secondary of the transformer. If the voltage is good and it was dropping with a load then disconnect the gas valve and check it. If it is the same as across the transformer then the gas valve is the problem. It is what we call a load no load check.0
Thank you Tim, I really appreciate the access to your expertise and your taking the time. If I may, just one more review and I think I'll be ready to take it on Without disconnecting anything yet, and with a call for heat, I'm going to check the PV(yellow wire terminal 1 in picture?) and MV (red wire terminal 3 in picture?)terminals at the module for 24 volts. Then I check these same wires at their gas valve PV and MV terminals. If the voltage drops at either location, I go to the transformer to check if the voltage drops there. If it does, I shut off the call for heat and check the transformer. If no drop is found, then I disconnect the(both PV and MV) terminals from the gas valve, have the thermostat call for heat and check for a voltage drop again at the disconnected wire ends. If none is found, it's the gas valve. Do I have it?0
Here are a few pictures of the (very dusty) gas valve.
Good catch Fred, I think you got it that valve knob needs to be lined up with the diamond shaped square so that it is full open. Try that John and see what you get?0
Will do! I'll let you know.0
So I turned the knob to the diamond(full Open) Got 24 volts at all the terminals(no voltage drop) with a call for heat,and it's working like a charm. The only thing that concerns me is that the home owner said that it started working fine again shortly after the day it acted up(Sunday ) with the valve still short of full open and that he or anyone else never went near it. Let's give it a few days before we claim victory. Thanks Guys!0
Oops! I spoke too soon. I was just informed that it happened again this evening. More tests under way. I'll keep you posted.0
JUGHNE Member Posts: 10,567The position of the valve knob should never affect the 24 Volt supply.. Could it be that this weekend your gas pressure supply could have dropped because of high demand due to cold weather?
Just from reading here and other info, I wonder if the national supply is suffering as the conversions from oil to NG seem tremendous.
The gas is there but not necessarily the pipe capacity.0
Interesting, but anecdotally , I doubt it. I maintain a good few properties with gas boilers in the same area, and this is the only one doing funny things. Also, the weather here in NYC wasn't terrible cold yesterday when this happened again.0
Gas pressure can be affected by water intrusion into old gas mains and then freezing. Building next door could be fine, but a dip in the main next door could cause water to pool and freeze. Old gas mains did not used to be installed below the frost line.
I've run into this several times on old 80-100 year old low pressure gas mains in Chicago, which is why the LDC has started a massive project to upgrade all these old mains.1
Hey guys. So recently, I bumped into this homeowner who informed me that this problem never went away! He lived with it last winter because all he had to do was shut the boiler off and turn it back on and it would run fine again for a while. He did however come to realize that when it does happen, the usual 24 volts(27 to be exact) drops down to about 12. So what would cause a voltage drop in the secondary circuit of the transformer? Would it be caused by any of the components that use 24 volts? Or is that something that only a drop in the primary voltage could cause?0
Jamie Hall Member Posts: 21,105Unless there's a terrific load on the 24 volt side -- unlikely, without that burning smell -- the most likely culprit is a poor connection somewhere. Which occasionally develops a high resistance, like when it gets damp. Look on both primary and secondary, and check all the grounds while you're at it. Come to think of it, it could also be a partially broken wire right at the transformer.Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England0
@Jamie Hall Okay, I'll check all the connections. thanks Jamie.0
Try replacing the transformer to a higher amp transformer....
A good test is to lightly hit the gas valve with your hand and see if it activates. The amp draw on the system is just not enough to fully fight the Springed relay. But just enough to open the valve slightly.0
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