Trane puzzle

[hoffa]

Had Trane 80% unit over 5 years old that developed an intermittent flame lockout after the first cleaning of the electostatic filter two weeks ago. The EFS was installed last June. Up until the EF cleaning, the 2 stage unit (which did actually use both stages) worked fine.

When checked out from the thermostat the unit would work fine. And the unit always started in winter mornings. Only randomly during the day would the unit lock out.

The regulator input pressure was 8WC and the stage 1 was 1.6wc and stage 2, 3.25wc both in spec. The hi out was .40wc.

The unit consistently failed on stage 1 when cycled by the Honeywell W8900 unit. That unit always cycles fan>stage1>stage2. Stage 1 would consistently fire only when the regulator stage 1 was set to 2.6wc, considerably out of spec. It always fired stage 2.

The final fix was an 8 cent part available at any local hardware store. Any guesses as to the problem? Questions welcomed.

[jacob perkins]

washer...

[markco]

An 8 cent wire brush to clean the cross-overs and flame sensor?

[hoffa]

perkins is the warmest

[jacob perkins]

Originally posted by hoffa
? Questions welcomed.

Where is hoffa?

[hoffa]

Another hint - a BIC stick was the tool of the day

[hoffa]

Got a job needs attending. So at the risk of being a spoiler, it was a #8-1/2 sheet metal screw.

The BIC showed the unit could light. There is an indented plate with an oval opening held in place by 4 screws to the chamger. One of these screws was missing from the factory. The tip off was that at one point between burners with the blower on only, the flame would dance instead of being quiet.

Any time the blower was on before a call for heat, air would come out of the screw hole. That amazingly was right at the angle needed to extinquish ignition.

So what masked the problem all these years? They didnt have that situation until they ran air during the day with the new Electostatic filter. no furnace over summer. Over the 6 months they ran, the ESF filter eventually got enough material in it that when they switched to heat in Winter our 8 cent extinquisher didnt extinquish.

Upon cleaning the ESF, blower velocity was just right and out went stage 1 flame only when the blower was on before a call for heat.

It always worked first thing in the AM because stage 2 was called and that was over the 2.6wc threshold at 3.25wc.

So why didn't this show up before ESF? MY guess is that it was rare when the had the blower on before heat and the material filters impeded the flow just right again.

Root cause - mfg defect: years old missing screw.

[beenthere]

The burner didn't shut off on high limit until the ESF was installed.

[hoffa]

If I undertand you question, the burner never shut off for lack of flame until the ESF was installed and then only if the filter load was just right.