No main burner

[rawkdw]

Hello,
I have a Miller model M1gb 056a BW with a Robert Shaw stepped gas valve 7200ercs. The gas is suppose to come on at 25% of flow then 14 seconds later kick up to 100%. The problem is it doesn't always kick up to 100%. It burns at 25% while the blower cycles on and off. I had the input gas pressure checked and it was 4.5" wc. I was told the valve was bad but I thought I'd checked with the experts first.

Thanks,
Rick
Cold in MI.

[Robert]

Hi Rick,

Natural Gas or LP ?

Have you checked the main burner orifice behind gas valve for blockage (spider-web-eggs) ?


Thanks,
Robert

[rawkdw]

Hello,
First, Thanks for the help. Its Natural Gas and will check for blockage in the morning.

Rick
Adrian,MI

[homebuff]

Hi Rick,

Natural Gas or LP ?

Have you checked the main burner orifice behind gas valve for blockage (spider-web-eggs) ?


Thanks,
Robert

Robert! David here.
Can you tell me where that orifice is located so I can check mine & how to remove it to inspect it?
That may be the reason why mine has some yellow flame mixed with the blue flame & a very low flame.
Thank's for you expertise & advice.
David

[rawkdw]

Hello,
Removed main burner assembly this morning and found no blockage of any kind. Removed orifice and looked down into valve and screen was clear. 24v at valve. Lit furnace and burner came on at 25% after about 20-30 minutes it kicked up to 100% flow. Yesterday it would'nt kick up at all.

Rick

[Robert]

Hi Rick,

Did anything fall out when doing this that may have caused a blockage ?


Let me know if it does it again, but after this, would need an hvac tech to test manifold gas pressure during cycle to see what it shows.


Thanks,
Robert

[rawkdw]

Robert,
Nothing fell out, I was very careful. and understand that it always takes 20 to30 minutes to kick up to full flow everytime there is a call for heat. I was ok with that as this is in my workshop. It did'nt did'nt kick up at all the other day which led me here. Manifold gas pressure is 4"wc during cycle.

Rick

[Robert]

Hi Rick,

Input gas pressure should be 7" to 8" wc and manifold gas pressure should be 3.5" wc.



It shouldn't take long for the gas valve to open to full stage pressure.



Thanks,
Robert

[rawkdw]

Robert,
My input pressure is only 4.5 wc. Would this cause my intermittent full burner more so then a bad valve?

Rick

[Robert]

Hi Rick,

That could be the problem or part of it. Get that corrected and see if anything changes.


Thanks,
Robert

[rawkdw]

Ok Thanks

Rick

[Robert]

You're very welcome, happy to help.


Take care and best wishes,
Robert