[nochaos]

Model number: CGU08016/ EVCON 1474-004
Ignition Controller: ROBERT SHAW HS780-34NL-306A

Hi guys,

I hope I can get some help here.
Here's what my issue is ... and my family wakes up in cold... We need a solution to this intermittent issue.
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i guys, I hope that the HVAC experts can help so that I can ensure that I am replacing the right part, if a replacement is needed at all..

EQUIPMENT: EVCON THE90 FURNACE
ISSUE: very frequent cycles and locked cycles where there's no ignition

My furnace is cycling a lot. I suppose that that is a good reason why my electric bills are high....

Anyway, the main thing right now is that the furnace will not come on at night and we're getting sick... while the draft inducer may soon burn out as it's on so often.

Here's what happened when the furnace does not ignite:
- The draft inducer comes on immediately when the Honeywell thermostat asks it to.
- The pressure switch closes and stays closed for the entire duration when the the draft inducer runs.
- The HSI does not light and the ignition process stops right there - while the draft inducer keeps running, the pressure switch is closed.
- After a reset by turning the power or sometimes the thermostat on and off. the correct ignition cycle takes place and the furnace runs fine.
- Normally the ignition issues seem to be more pronounced overnight.
- NOTE: even this "reset" works: while the draft inducer runs I take the pressure tube out and plug it back in. The pressure switch obliges and opens and then closes back. The board does the job properly, the HSI lights out, etc -- all ok.

What gives? I would think that the issue is the Robertshaw HS780-34NL-306A ignition control module and that I would have to replace that, but since it is pretty costly I would like to be sure before I buy.

Is there any way to be absolutely sure if the controller is the issue?
I am positive that the pressure switch and the inducer close the circuit right.
Is there any OTHER input that the controller looks at before deciding to turn on the HSI?

Thank you very much.

Eugen