Gas Valve

crash2009

Woke up to a cold boiler room this morning.  The pilot was out.  Set the dial to pilot and lit it.  Wouldn't stay lit so I called repair.  While I was waiting for repair, I noticed that the electric part (which is bolted to the gas valve) was warm, in fact the heat from the electric part was heating up the actual valve.  I managed to guess that the electric part was overheated, and I suspected a short or something inside it.  So, I shutoff the electrical to the boiler.  When I shut of the electrical, I heard a couple clicks and turned it back on again.  Funny part is the damper closed, the damper was open all night.  This made me think that something had failed during firing of the boiler, and was glad that I had called repair to check it all out.  Repair and I looked at the data from the data logger, it appears that the boiler was trying to fire all night, but never succeded.  Eventually, after 3 or 4 missfires, it put out the pilot light and went to sleep.



Repair got here and swapped out the thermocouple.  Gave the gas valve a few good wacks with the crescent wrench, and got it going again.



I have decided to replace the gas valve.  Is there an upgrade or something else I should be thinking about?  Or just get the same thing I had before?



Weil McLain EG-55 with a VR8300C4050 gas valve.

Mike Kusiak_2

Thermocouple

Sounds like the thermocouple might have been the problem. The thermocouple pilot safety is completely independent of the electrical actuator controlled by the thermostat. If the pilot goes out or the thermocouple fails, the safety electromagnet releases and cuts off gas supply to the valve. If the thermostat calls for heat, the normal valve actuator coil will be powered, but since the gas supply is cut off, the burner will not fire. This sounds like your situation. Since the burner never fired, the thermostat kept calling for heat which is why the damper stayed open and the valve coil was warm, since it was powered up all night.



If you want to replace the valve, I would use the identical model. The VR8300C is the latest standing pilot valve with dual redundant shutoff which meets the latest safety codes.



Here is the manual for the similar VR8200 which explains the operation of the valve and has some really informative drawings of the internal construction.



http://customer.honeywell.com/techlit/pdf/68-0000s/68-0046.pdf

crash2009

Slowly understanding

Thanks Mike, you have somehow untangled almost all the questions I had in my mind, and answered them.  So most of these oddities that I observed were just symptoms of thermocouple failure.  



Any thoughts on the lascar chart?  Looks to me like the thermocouple died around midnight and the pilot stayed lit for a few hours.

Hap_Hazzard

By the end of the first line of your post

I was thinking, "thermocouple." These things go all the time. I keep a spare hanging in the furnace closet. When you look in there and see it glowing red it's a wonder they last as long as they do. Your gas valve should be fine.

Hap_Hazzard

The pilot can't stay lit if the thermocouple opens.

But if the burner is on, it will keep burning until the end of the cycle. Once the burner shuts off, that's all she wrote.

crash2009

Thermocouple

If the thermocouple fails, (stops working) Is the pilot supposed to go out?

Hap_Hazzard

Yes.

When you light the pilot, you need to hold down the control knob until the thermocouple gets hot enough to generate an electrical current. If you don't get it hot enough, or the thermocouple is bad, it won't stay lit. If you have a voltmeter you can easily test it. The exact voltage doesn't matter and is temperature-dependent. Just look for the voltage to rise as the temperature increases. If it's bad you get nada.

crash2009

Thermocouple

So then this picture (above) of the Lascar data logger, represents a failing thermocouple, not nescesarily a thermocouple that has failed.  If a thermocouple is failing (about to fail completely) Will it cause the valve to allow only a small amount of gas into the burner?  There was a small amount of gas burned during the night, just enough to raise the stack temp 2 or 3 degrees F.  Just trying to figure out if this is normal.

Mike Kusiak_2

Lascar plot

I don't think the plot shows the thermocouple failing but possibly the vent damper opening periodically. When the damper opens , it allows warm air from the boiler to go up the chimney, warming the flue pipe a few degrees. Do you have an electronic LW cutoff or feeder that drops the burner periodically while checking level? That might explain the spikes on the graph.



I have a feeling the thermocouple failed at the beginning of the graph or before because once it drops out the valve magnet,  the valve closes and cannot pass any gas to the pilot or otherwise until manually reset with the button. Its impossible to just pass a little gas, its all or nothing.

crash2009

In stock spare?

 The damper opened up and allowed some room air into the flue, then it closed.  The damper continued to open and close all night.  That makes sense.  I guess I'm over it. 

I have a McDonnell and Miller water feeder and a Safegard 400 lwco.    

Thanks for the manual.  That is really helpful toward my attempt to understand how the valve works.  I was concerned that the actuator got too hot and burned itself out or reduced it's life expectancy.  But I guess it's designed for exactly this scenario.  It would be expected to outlast several thermocouples. 



While gas valve shopping today, I noticed that they are not readily available.  24-48 hour delivery, or 30-60 miles to pick up.  Is it common in the heating community to keep a spare in stock?

Hap_Hazzard

I wouldn't think so.

Gas valves don't usually fail suddenly, and since they can run anywhere from $100–$300, that's a lot to spend for something you'll probably never use. It would be sort of like keeping a spare fuel pump for your car. I think it's definitely worth it to keep a spare thermocouple, and if replacement parts are available for your model you might put together a rebuild kit.

Steamhead

The VR8300C

is a "step-opening" valve that opens partway when it first comes on, then rises to full fire. This helps avoid some light-off problems on certain units. Make sure you get another VR8300C, not the more-common VR8300A that just opens wide right away.



And- have a PRO set up the burner with a digital combustion analyzer, to make sure the burner is set up properly with the new valve.

crash2009

Oh Yea

I completely forgot about setting the valve up with an analyzer.  This falls testing results would be null and void with a new valve.  By the way Steamhead, you will be happy to know that when I had the testing done this fall re "barometric damper on atmospheric steam", Dennis said "I can't improve upon outstanding" His only suggestion was that my fresh air was a hair too small.



I have noticed the step-opening of the existing VR8300C.  The valve starts out slow then opens to it's max.  I think that is a good feature to have.  I made a premature decision to replace it.  As far as I can tell so far the valve itself has done no wrong.