Weil Mclain CGa Boiler Firing Issue


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Old 11-08-10, 12:01 PM
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Weil Mclain CGa Boiler Firing Issue

I have a Weil Mclain CGa boiler that is only a couple of years old. I drained the boiler and shut it down over the summer, I just tried starting it up yesterday and I am having issues.

First I flushed the whole system out and filled with new water. Second I lit the standing pilot without any issue. Then I turned power on to the boiler and adjusted the thermostat to a high enough temperature to kick the boiler on. Initially it turned on as expected, the circulator started pumping, the automatic vent damper opened up and the main burners kicked on. The system fired for a couple of minutes and then stopped. I checked the temperature gauge and the water reached about 120 degrees. The aquastat is set to 180 degrees. I felt the pipes coming out of the boiler and they were not warm. The circulator kept pumping. The only way I could get the system to fire again is by shutting it down by adjusting the thermostat lower, and letting it sit for about an hour. Once I adjusted the thermostat higher again the boiler would fire for a couple minutes and shut off again. I cannot get the boiler to fire long enough to heat the water to a hot enough temperature.

Any ideas?
 
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Old 11-08-10, 03:57 PM
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Steve, before we get on to the firing problem, can I ask why you drained it when you shut it down? Not only is that not necessary, and makes all that extra work for you in the fall time, it is actually a bad thing. Here's why... when you run water in a closed heating system, all of the oxygen is driven out of the water and vented to the atmosphere. Water without oxygen will not rust or corrode anything. By draining the system and allowing all that air that is now in there is allowing rust and corrosion to form.

Bottom line, just shut it off. Do not drain it.

more later...
 
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Old 11-08-10, 04:13 PM
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There are a number of things that can cause this. In line with the gas valve are some safety switches. There are a 'SPILL SWITCH', a 'ROLLOUT SWITCH', and the switch inside the vent damper to prove it is open. You may also have a LWCO (Low Water Cut Off) switch installed. Any one of these tripping indicates that there is a problem...

There could be rust and junk on top of the burners causing poor combustion and soot and rust in the flue passes causing poor draft which would trip the flame 'rollout'.

There could be a (now dead) family of squirrels in your chimney that would cause flue gas to escape around the atmospheric vent on the flue pipe and trip the 'spill switch'.

Your vent damper might be malfunctioning.

If you have the optional LWCO, it could be sensing (either actually, or falsely) a low water condition.

What is your skill level? Do you feel confident?
 
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Old 02-24-15, 06:27 PM
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I am suffering from similar symptoms, and since this guy has disappeared, i will pick up where he left off...

I have a CGa, and the burner will go on for 2 minutes or so before it trips off for the next 10 minutes, even as the thermostat calls for heat. When it trips, the power to the control module completely dies, the power light is not even lit. I mistakenly thought i should replace the control module, which i did, with no improvement.

Subsequently i have noticed that it is the LWCO (Safgard Model 1100) tripping the module, the power dies when the low water indicator comes on. Pressing the test button on the LWCO triggers an identical response. Pressure when the boiler is off is about 16 psi, and the water supply valve is constantly open. Do I need to replace the LWCO? Is there anything else that could cause this?
 
 

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