Weil McLain boiler short cycle gas valve

markman77

GV 1013-200 controller.
Boiler cycles thru startup sequence, no flashing lights.
Igniter comes on, gas valve opens, burner lights, igniter turns off, burner remains lit for two to twenty+ seconds, all lights steady on. Then gas valve closes.
Cycle repeats immediately ( never locks out). Flame runs for variable length of time.
Sometimes after doing this a dozen times or so it will remain on and normal heating sequence works (cycling based on return water temp)
Replaced controller three years ago, Installed jumper to eliminate the always flashing #2 light.
Boiler is About 25 years old. New circulator and water temp switch Two years ago.

Could it be a gas quality/Orifice issue?

JUGHNE

My first guess would be the flame sensor/rod.
The igniter may have double duty as the flame sensor also.
If so then I would replace the igniter, especially if it is the original.
If not, then having a spare igniter is not a bad idea.

markman77

Thanks! New igniter last year. 

I’ve wondered at references in various documents to ‘proof of flame’ as there is no separate flame detector either physical or in the  wiring diagram.  

Does the igniter need to be ‘hot enough’ or how else does it serve double duty as a flame sensor? 

JUGHNE

IIUC, the igniter glows red hot and then is de-energized when the gas valve opens. The board then switches the HSI from heating function to the sensing function.
The after glow of the red hot surface is what lights the gas.

Another part of the flame sensing circuit is a good ground path to the module from the burner. Re-seating connections may improve that path.
Also HSI's that can do ignition may not always do sensing well.

What boiler is this, is there an inducer fan with pressure switches?

markman77

HE 2, induced draft fan and switch. Fan pressure sequence seems fine.
Thanks for the info, I’ll give it a test.
Having a spare igniter is a good idea, I’ll Check connections, get a new igniter And see what happens.

HVACNUT

It might be going into lockout and you don't even know it. It automatically restores normal sequence of operations after one hour. Like @JUGHNE said, check the grounds. Very important for flame rectification. 
After a few on and offs, all seems well? No banging or knocking? System and bypass circs are working? (Under the jacket)
Also make sure all molex connectors and wires into them are snug.
25 years. When was the last time it had a good maintenance?

unclejohn

Normally its the pressure switch fluttering. It happens so fast it won't show up as a fault. Try jumping the switch and see if it stays on.

Jacityheating

Hi Mark,

What manufacturer and model burner control aka flame supervision is being used on this boiler? What's the burner manufacturer and model? What automatic reset switches are within the burner limit string? If the flame signal is dropping below 1.5 vdc then the burner will trip out. What flame sensor are you using flame rectification or ultra-violet?

Jason St. Clair

markman77

Wrapping this up ( i replaced the 25 year old boiler with a Bosch Greenstar). Greatly appreciate all the suggestion. What i concluded was that i have an intermittent gas supply issue that caused the flame to stand way off the burner so the rectification signal wasn’t strong enough. This is based on my gas stove which periodically exhibits the same behavior and that if i reduced the afterfire air flow velocity by opening the burner shield, the problem was greatly reduced.
Bad utility regulator? Low quality NG from the utility (they often dilute their gas in the winter)? Not sure.

ratio

Thanks for the follow-up!

I'd have no trouble condemning the house regulator after observing something like that, although I would probably throw a gauge on the inlet side & try to see exactly what's happening. Overpressure enough to lift the flames off the burner isn't terribly safe, I hope you had it looked in to?

DNAS2019

I am troubleshooting a boiler Weil MC same exactly issue and I suspect the control board which is the igniter module in this case, same boiler as the one stated here, now reading this made me change my mind to replace the HSI even though it looks brande new but may not be the one recommended, by the way pressure switch has been properly by passed after the inducer blower starts and the module proves the switch was open, so it cant be venting issues or pressure switch problems.