Help shooting Lennox Boiler


  #1  
Old 10-08-09, 04:49 AM
P
Member
Thread Starter
Join Date: Oct 2009
Location: PA
Posts: 4
Received 0 Votes on 0 Posts
Help shooting Lennox Boiler

I would certainly appreciate any input to t-shoot a Lennox GWB8 boiler that intermittently fails to fire. When its cold, the flame roll-out is OK, the blocked vent is OK, damper is open, 24V from aquastat is present and a stat is calling for heat. Seems to be either ignition control (UT Elec) or gas valve, but how to isolate without replacing both? Thanks for any help you folks can offer.
 
  #2  
Old 10-08-09, 03:22 PM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,539
Received 4 Votes on 3 Posts
Not real familiar with the Lenox, and they apparently don't see fit to provide the manual on-line... but,

Question: Does the ignition light the pilot OK?

It appears that this boiler has a draft inducer fan, and a pressure switch system that proves when the draft through the boiler is acceptable to fire it... I would suspect that fan/motor, or the pressure switch as the problem if everything else checks out.
 
  #3  
Old 10-09-09, 04:17 AM
P
Member
Thread Starter
Join Date: Oct 2009
Location: PA
Posts: 4
Received 0 Votes on 0 Posts
Hi NJT,
No there is not a draft inducer on this unit but there is an automatic damper with limit switches that must be satisfied and they are OK. This morning the unit was cold and I turned the gas valve control knob off then on and cycled 120VAC power to the furnace and it fired right up. I am pretty certain it is either the gas valve or ignition control box failing but I am at a loss as to how to isolate the two. There is a cable connecting them with four wires, Gnd, MV, PV/MV and PV. I am guessing Main Valve, Pilot Valve and a common. I'll try to break those out with jumpers and look for 24VAC going to those wires. If present, gas valve bad, if not present. Ingiter bad. Does that sound reasonable? I hate to buy both! Pilot does not try to light when unit fails.
 

Last edited by pct_elect; 10-09-09 at 04:43 AM.
  #4  
Old 10-09-09, 03:09 PM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,539
Received 4 Votes on 3 Posts
I thought they mentioned the inducer and pressure switch in the limited info Lenox provided on the website... maybe I was looking at the wrong model, or the newer ones have it...

I'm not a good gas guy really, but the way I think the ignition sequence should go... control opens PV, and turns on ignition.

When pilot lights, flame rod senses flame, and opens MV, which then lights the main burner...

So, if you are stuck at 'no ignition attempt', then either the control has 'locked out' for some unknown reason, or the control itself is intermittent.

Checking for presence of 24VAC at the PV and MV is good diagnostic information though.

Have you tried the 'tapping test' yet? You know, gently tapping around with the handle of a screwdriver?

And, check the grounds... I believe a good solid ground is crucial to the operation.

What controller is in your system? 8600 ?
 
  #5  
Old 10-12-09, 04:29 AM
P
Member
Thread Starter
Join Date: Oct 2009
Location: PA
Posts: 4
Received 0 Votes on 0 Posts
Well I haven't definitely isolated the probable faulty yet, but for the record in case anyone else has a unit like this...tapping test don't help.
Aquastat is HW L8148 and ignition control is UT Electronics 1003-620A. An electric spark lights the pilot and I believe as long as the module senses current flow to the spark it opens the Main Valve. There is not a flame rod. The ground was OK between the Ign control and the gas valve, but there was corrosion at the point the Pilot tube/sparker assy. screwed to the burner tubes. Friday I had that apart to clean, visual inspect and re-assemble. The unit fired OK all weekend. This unit has been troublesome since install early 2006. I am not quick to fault Lennox quality, but every fall is a battle.
 
  #6  
Old 10-12-09, 03:11 PM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,539
Received 4 Votes on 3 Posts
A quick Google didn't turn up specs on your control... any more info on it?

There has to be something that proves the pilot is lit before the MV will open. Simply relying on the current in the ignition spark is not enough. That's not proof that a pilot exists.

Maybe the corroded ground was the problem...
 
  #7  
Old 10-13-09, 09:47 AM
P
Member
Thread Starter
Join Date: Oct 2009
Location: PA
Posts: 4
Received 0 Votes on 0 Posts
Thumbs up

No info on the UT Elec control, but if the wire going to the spark is pulled while the unit is fired, the main valve closes and fire goes out. Monitoring current flow to ignition spark doesn't seem so fail-safe to me either, but I guess if it can be monitored to remain in the slot between a dead short and an open, then it would have to be a fairly reliable indicator, eh? Anyhow it hasn't failed since cleaning, I guess that is key to maintaining this unit.
 
  #8  
Old 10-13-09, 02:37 PM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,539
Received 4 Votes on 3 Posts
I believe the flame rod is part of the ignitor, so that makes sense.

Grounds are crucial because of the very small amount of current that is generated by the flame rod... a little bit of resistance and there goes the signal!

I think you'll be OK now...
 
 

Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: