Boiler occasionally fails to ignite

prwood

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?

prwood

Update: Looking at the company that makes the pilot assembly, it appears the bend in the spark electrode is normal in some cases (they don't have the exact model here): https://pse-usa.com/product-types/pilot-burner-assemblies/

prwood

Found the replacement part online for $60, so it wouldn't be a huge risk to just replace it if it keeps failing: https://supplyhouse.com/Weil-McLain-511-330-218-Pilot-Burner-Assembly

EBEBRATT-Ed

Remove the pilot assembly and clean the flame sensor with fine steel wool.

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

unclejohn

Like ED said a good cleaning should do it. Clean sensor not the bent igniter. Sometimes you can clean them without removing the pilot. Also flakes of rust will sometimes fall onto pilot and mess things up that would have been cleared when you took it out.

prwood

Hi all. Thanks for the feedback. The boiler failed to ignite again yesterday, so this time I removed the pilot assembly and cleaned the sensor with fine steel wool. I also cleaned the contact surfaces on the sensor assembly and where it mounts to the flame tube (don't know if that's the technical name). Reinstalled and it ignited properly. Time will tell if this fixed it - it seems to go about 1.5-2 weeks between failures.

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.

prwood

prwood said:

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.

Just bumping this up in case anyone has a comment on these additional questions.

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.

ratio

Your precautions for the pilot line are fine. It's not terribly delicate, if you're not pulling it out & rebending it every few weeks it should last the life of the boiler. A slightly bigger concern to me is getting the compression nut back on without cross-threading it. Take your time & make sure the pipe's going in true.

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.

prwood

ratio said:

Your precautions for the pilot line are fine. It's not terribly delicate, if you're not pulling it out & rebending it every few weeks it should last the life of the boiler. A slightly bigger concern to me is getting the compression nut back on without cross-threading it. Take your time & make sure the pipe's going in true.

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.

Thanks. In my case I left the pilot line attached while moving the pilot assembly, so there was no worry about rethreading it. I've had enough experience with badly threading nuts in other applications that I'm pretty obsessive about it now if it does come up.

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.

prwood

prwood said:

Hi all. Thanks for the feedback. The boiler failed to ignite again yesterday, so this time I removed the pilot assembly and cleaned the sensor with fine steel wool. I also cleaned the contact surfaces on the sensor assembly and where it mounts to the flame tube (don't know if that's the technical name). Reinstalled and it ignited properly. Time will tell if this fixed it - it seems to go about 1.5-2 weeks between failures.

It's been 3 weeks since cleaning the sensor with steel wool, and I haven't had any problems since then. The boiler has been igniting reliably. I feel pretty confident that this has fixed the issue.

Thanks for all the help!