It's doing it again...

Jamie Hall

that is, the Carlin which fires my Weil McClain.

What it does is sometimes (three times this evening) on a call for heat the burner will run through the pre-purge, fire up, and run for 15 seconds or so -- and stop dead. No post purge. Then after about 15 seconds or so -- long enough to make you really nervous -- it will run the pre purge again and fire up and run perfectly.

I haven't caught it in the act, so I can't tell you what the lights on the control are saying.

This is the first time this year its done this, although it did it from time to time last year.

The burner is serviced by Charles Garrity, whom I regard as one of the best in the business, so...

Any ideas as to what might be going on? And what to do about it?

icesailor

Is it a 602000 control?

Sometimes, when the ohms are high as far as what the Cad Cell "sees' , it might be dropping out, or the flame intensity drops when the ignition drops out. If the ohms are up over 1,000, it can get twitchy in some applications. The hardest one I had was with a 568 boiler. Be sure that the inside of the tube is as clean and bright as you can get it. Dirty ones can absorb light and give a false reading.

IME.

Jamie Hall

I kind of think you may be right, Ice. If it gets worse, I'll pester Charles. Oil burners I don't play with (I know my limits on some things!)

icesailor

Oil is far easier than gas.

Take your trusty Multitester, and you'll have to figure this out. You can't start the burner with both yellow "F-F" wires/terminals jumped, but it will start with one side of the jumper off. Start the burner. Once it is established, connect the other side of the jumper on the other "F-F" terminal. The control thinks it is seeing a flame. Then, put the two yellow wires on the cad cell leads. Read the ohms. Even if you can see a flame through the tube, the eye may not see enough. You can't see the brightness that the cad cell eye can.

A new C554a Cad Cell Assembly is cheap money. Get a new one. Compare it to the old one. If the readings are close, it isn't seeing enough light.

Best to check it when it first starts and after the ignition stops. Look for a difference. Excessive draft can cause problems if it sucks the flame away from the retention head.

At least you can see what you are doing. With gas and a Mod Con, its like trying to open a combination padlock inside a bag and you can't see what you are doing.

IMO.

If you're brave, make some adjustments. See if the flame gets brighter and the Ohms go down.

Jamie Hall

Gotcha. I'll give it a shot!