Weil Mclain CGa gas boiler - intermittent firing in summer

[mikey00]

I have a Weil McLain CGA gas boiler installed in fall 2001. Attached is a WeilMcLain indirect fired hot water heater. It performs well all winter and in the in between months when the boiler gets fired at least a couple of times a day. Problem is in summer when the indirect water heater only fires the boiler about once a day. The water heater thermostat calls for hot water, the pilot light lights and goes out before the main burner fires. The boiler control senses no flame and waits 5 minutes and repeats the process. The main burner will usually fire on this second attempt but sometimes even requires a third try.
Before I understood what was happening I tried the water heater thermostat. Next I realized the boiler wasn't firing so I tried the automatic vent damper. Then I even tried locking it open. I should also add that the chimney is normal with good draft and no down draft. Basement is clean, not really damp, has dehumidfier.
Next I replaced the pilot light assembly with the aluninum gas tube back to the gas valve. Weil McLain tech support was of no help but I did talk them into sending me a new boiler control unit even though I was out of warranty by then. Still no good.
My next suspect is the gas valve. There are 2 adjustment screws on it, pressure regulator and pilot light but neither have no effect on the problem. Currently my only solution is to manually fire the boiler a couple of times a day. Any ideas?

[NHMaster3015]

Have you thought of calling a gas service tech?

[mikey00]

I would like to if I could find someone. Do you know anyone in the Morris County NJ area competent enough to troubleshoot this intermittent problem? Most want to sell new boilers or fix easy problems. I had my installer back twice to look at this problem after install. Wasn't impressed. I also spoke to different techs when I was at different job sites doing other work in my profession and most of them just wanted to guess and change the gas valve. I was already thinking of doing that.

[plumberscrack]

If you don't already have this, please print it out and keep it near the boiler for reference

http://www.weil-mclain.com/downloads/literature/cga/cgaboilermanual.pdf
on page 37 you will find a sequence of operation for spark ignition boilers.

When you replaced the pilot assembly did that include the pilot sensor?

The module won't lockout on flame failure, only on voltage issues but this doesn't sound like your issue if it's trying to relite every 5 minutes.

Watch the lights on the boiler control. That will lead you to the problem.

From what you are discribing it does sound like a gas valve and/or pilot sensor issue but it could be a dozen other things or a combination of several. Any competentant tech should be able to diagnose this within a few minutes but only if the problem presents itself while he's there. In any case, he should be able to rule out some things, ie, gas pressure, damper micro switches, improper wiring and shorts.

How is the indirect heater controlled? through a separate zone or pump relay control?

[rjm78]

I haven't thought ths through enough but are you sure about the draft? Summer doesn't allow for the flue to warm up. Also, what's the flame sense? Sensor or rectification. Sensor and be cleaned, rectification usually is because of a bad ground to unit.

[mikey00]

If you don't already have this, please print it out and keep it near the boiler for reference

http://www.weil-mclain.com/downloads/literature/cga/cgaboilermanual.pdf
on page 37 you will find a sequence of operation for spark ignition boilers.

When you replaced the pilot assembly did that include the pilot sensor?

The module won't lockout on flame failure, only on voltage issues but this doesn't sound like your issue if it's trying to relite every 5 minutes.

Watch the lights on the boiler control. That will lead you to the problem.

From what you are discribing it does sound like a gas valve and/or pilot sensor issue but it could be a dozen other things or a combination of several. Any competentant tech should be able to diagnose this within a few minutes but only if the problem presents itself while he's there. In any case, he should be able to rule out some things, ie, gas pressure, damper micro switches, improper wiring and shorts.

How is the indirect heater controlled? through a separate zone or pump relay control?
Thanks for the PDF of the manual. I already have the printout that came with the boiler and have been through the light troubleshooting sequence many times. The lights kind of leave you hanging. I get power, tstat, limit and damper lights but not flame. At that point you can't tell why you didn't get flame light. Is it because damper closed? Is it because pilot went out? Or pilot wasn't sensed? Or gas valve didn't turn on main burner? After 5 min sequence will start again and this time it will go all the way to flame and everything will be good.
As far as your other questions go: The sensor was included in the pilot light assembly. I thought for sure that was going to be it, but no.
I don't get any module lockout. Everything always retries after 5 minutes.
The indirect heater is a separate zone with its own pump controlled by a Argo ARM-3P three zone switching relay module with priority. Water heater is on priority. Any zone trying to fire the boiler after having been off for a day will have the same problem.
I could have a tech come in and check gas pressure but I don't see the point in checking damper micro switches (remember I changed the whole assembly), improper wiring or shorts. Remember everything works fine as long as the boiler fires at least 2 times a day. It has been this way from 2001. If I do have a tech come in I have about an 80% chance of being able to show him the problem once. After that it is gone for another day.
I think my next step will be to monitor the 24v at the gas valve for the pilot and main burner and see if I can determine anything there.
Another poster mentioned the draft possibility being that it is summer. I could crack open a window and pre heat the flue just to eliminate this possibility but I don't think that is it.