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Boiler occasionally fails to ignite

Our house is heated with a Williamson GSA boiler (GSA-200-N-IP), which we had installed four years ago. It has worked flawlessly up until two weeks ago. We first noticed a problem when our system didn't heat up in the morning like it usually does. Our thermostat was calling for heat, but no heat was being produced.
I checked out the boiler - water level was good, the damper was operating properly. I switched the heat on and off several times, and what I observed was that the ignition would spark for 10 seconds or so, and I could hear and see the pilot flame burning, but the main burner did not come on. The spark and pilot flame would then shut off. I repeated this several times with the same result.
I turned off the power to the boiler for further diagnosis. I looked through the troubleshooting sections in the user manual, and in the spark ignition manual followed the flowchart for "CHART 3 - PILOT LIGHTS - Main valve will not come on - with or without damper". (page 13 in this manual) This led me to check whether the SENSE wire was wrapped around any pipes or accessories, and whether it was securely attached to the sense terminal and pilot assembly. The connections all looked good - it was very firmly attached at the terminal, and seemed to be hardwired to the sensor. I did notice that the sense wire was coiled around the gas line going to the pilot assembly. Not sure if this is normal. In any case, I tried to move the sense wire a bit so it was touching as little as possible.
After doing this, I turned the power back on and tried calling for heat again. The spark ignited the pilot flame, and the main burner then kicked in successfully. The boiler continued operating normally for the next two weeks. However, this afternoon we had the same issue again. This time, after powering off the system, I took the extra step of removing the pilot assembly and inspecting it. You can see it in the attached photo (click to view larger).

The first thing I noticed is that the spark electrode appeared to be bent. I am assuming it's not supposed to look like that, but I could be wrong! However, I'm not sure if that's the cause of the issue, because the pilot flame does ignite properly every time. It just seems that the pilot flame isn't picked up by the sensor every time. But maybe it's related?
This time when I put everything back together, I unwrapped the sense wire from the pilot gas line so that it is no longer touching it. It looked like when it was installed, it had been very deliberately routed underneath the gas line. Once I started everything back up, the heat came on as expected, just as it did the last time I got in and jiggled some wires.
In any case, I'm not really sure if anything I'm doing (basically just taking off the boiler cover panel and jiggling the sense wire) is actually causing the sensor to work, or if it's just pure luck and an intermittent failure. I went further down in the flowchart and was able to rule out some of the other possible causes - cracked ceramic (no), wire shorting to a metal surface (no). If it fails again, I'll get out the multimeter and run some of the other tests. If there's a problem with the sense wire, it sounds like the whole pilot assembly has to be replaced.
Any suggestions or advice?
I checked out the boiler - water level was good, the damper was operating properly. I switched the heat on and off several times, and what I observed was that the ignition would spark for 10 seconds or so, and I could hear and see the pilot flame burning, but the main burner did not come on. The spark and pilot flame would then shut off. I repeated this several times with the same result.
I turned off the power to the boiler for further diagnosis. I looked through the troubleshooting sections in the user manual, and in the spark ignition manual followed the flowchart for "CHART 3 - PILOT LIGHTS - Main valve will not come on - with or without damper". (page 13 in this manual) This led me to check whether the SENSE wire was wrapped around any pipes or accessories, and whether it was securely attached to the sense terminal and pilot assembly. The connections all looked good - it was very firmly attached at the terminal, and seemed to be hardwired to the sensor. I did notice that the sense wire was coiled around the gas line going to the pilot assembly. Not sure if this is normal. In any case, I tried to move the sense wire a bit so it was touching as little as possible.
After doing this, I turned the power back on and tried calling for heat again. The spark ignited the pilot flame, and the main burner then kicked in successfully. The boiler continued operating normally for the next two weeks. However, this afternoon we had the same issue again. This time, after powering off the system, I took the extra step of removing the pilot assembly and inspecting it. You can see it in the attached photo (click to view larger).

The first thing I noticed is that the spark electrode appeared to be bent. I am assuming it's not supposed to look like that, but I could be wrong! However, I'm not sure if that's the cause of the issue, because the pilot flame does ignite properly every time. It just seems that the pilot flame isn't picked up by the sensor every time. But maybe it's related?
This time when I put everything back together, I unwrapped the sense wire from the pilot gas line so that it is no longer touching it. It looked like when it was installed, it had been very deliberately routed underneath the gas line. Once I started everything back up, the heat came on as expected, just as it did the last time I got in and jiggled some wires.
In any case, I'm not really sure if anything I'm doing (basically just taking off the boiler cover panel and jiggling the sense wire) is actually causing the sensor to work, or if it's just pure luck and an intermittent failure. I went further down in the flowchart and was able to rule out some of the other possible causes - cracked ceramic (no), wire shorting to a metal surface (no). If it fails again, I'll get out the multimeter and run some of the other tests. If there's a problem with the sense wire, it sounds like the whole pilot assembly has to be replaced.
Any suggestions or advice?
Our equipment: Williamson GSA GSA-200-N-IP gas-fired steam boiler; install date October 2016
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Comments
Make sure that all the screws and pilot mounting surfaces for the pilot assembly are clean as the flame sensing current goes through the ground circuit as well
Couple other questions:
- Is there a proper way to route the spark, sensor, and gas lines running to the pilot assembly, or does it not really matter? In terms of what if anything they are allowed to touch, whether they should be looped around anything, etc.
- I haven't worked with a semi-flexible metallic gas line like the one going to the pilot assembly. I have only moved it on two occasions, but I'm a bit worried that moving it too much could stress it. Hopefully I won't have to move it much more, but I'm just wondering how durable it is and if it requires any special handling, beyond just making sure not to crimp, kink, or nick it.
The boiler has been firing correctly for the past week. If it can go for another couple of weeks then I'll feel confident that cleaning the sensor has fixed it.
Your symptoms are classic dirty flame rod. Another popular cleaning method is to rub it down with a dollar bill—easier to source a bill than steel wool. That said, a spare flame rod is a small investment with a big payoff if you need it.
Luckily we had bought a ton of fine steel wool when dealing with a mouse problem, so I have plenty on hand for cleaning purposes. Actually have more steel wool than cash on hand.
Thanks for all the help!