Hello,
I have a problem with the intermittant pilot on my ~9 year old gas fired boiler that came with my house. It is a Vaillant boiler #GA92-120PV, with a honeywell gas valve #VR8204A, a Honeywell spark ignition control box #S8600F, and power vent. The boiler is at 8500 feet elevation, and has a label stating it has been set up for 5000 feet operation. Several years ago, not long after I bought the house, I noticed the pilot was not igniting reliably. The ignitor was constantly sparking and the pilot gas looked like it was attempting to light off, but just wouldn't light. It appeared as if the pressure of the gas was actually blowing out the pilot flame as it was trying to light off. I had a serviceman look at it and he showed me how to readjust the pilot pressure, which seemed to solve the problem. Now the problem has returned intermittantly, mostly after the boiler has been firing awhile and the combustion chamber is hot. When the boiler is cold, the ignitor sparks, the pilot lights and the main burners come on normally, all occurring in about a second or two. I tried to readjust the pilot pressure, but I see absolutely no change in the pilot flame size regardless of where the adjustment screw is. Also, the pilot flame does not appear to be overly large (no yellow tips at all). I have cleaned (with 1200 grit sandpaper) the ignitor sensor to no effect... Everything else seems normal, the burners light off and burn correctly once the pilot actually lights.
Any ideas? Thanks for providing this service and website!

There is a very small orifice inside the pilot assembly, if you romove the pilot line you will see it inside, I bet it needs cleaned good, there are special tools to clean it but compressed air usually works very well.

There is a very small orifice inside the pilot assembly, if you romove the pilot line you will see it inside, I bet it needs cleaned good, there are special tools to clean it but compressed air usually works very well.

Sorry, I neglected to mention I recently cleaned it, along with the igniter. I should mention that when it is acting up, I can get it to light immediately if I ever so slightly turn the gas valves' control knob towards the off position. Almost seems like too much gas is coming out... shouldn't the pilot gas pressure adjustment make a significant change in the size of the pilot flame? I get no difference at all regardless of where I set the screw...
Thanks!

Yes it should make a significant difference. It's hard to tell from hear if the orifice is plugged or damaged. If it is opening the pilot valve, the gas valve is working and the problem is in the pilot assembly. Input and output pressure of the gas valve could also be helpful to know.