Original message
| jfevans
 |  "Honeywell 90+ problem (I think)"
, posted Mon 3 Nov 16:13  
this weekend I had an issue with the furnace not coming on, a Honewell 90+ with a SV9541M smart valve. I tracked it down to the pressure switch vacuum hose, ( nice flow chart, helps a lot) replaced it and on she goes,,, the current sequence is:
turn thermostat on, combustion blower comes on, then the pilot valve and then the main valve, then the fan, BUT, the combustion blower never turns off, so it is blowing hot are out off the vent pipe all the time, IS THIS SUPPOSED TO BE THIS WAY, or should it shut off after the furnice fan is on and running....
thanks
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Replies:
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| theduke03
| "Re(1):Honeywell 90+ problem (I think)" , posted Mon 3 Nov 19:13
I could be crazy but I think the combustion fan is neccessary for combustion. It should run until the call for heat has ended.
"My dad was the most feared furnace fighter in Northern Indiana."
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| | jfevans
| "Re(2):Honeywell 90+ problem (I think)" , posted Mon 3 Nov 19:51
OK, I was thinking it was for clearing any gas out of the heater system before the pilot came on and fired the gas, I don't see way this would be on all the time. it pulls are from the heater plenum and sends it outside through a vent. After the heat comes on it is still on, sending hot air outside to warm the local animals
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| | theduke03
| "Re(3):Honeywell 90+ problem (I think)" , posted Tue 4 Nov 18:18
The air being vented outside is combustion gases, hence the term: combustion fan motor. That air is not from your plenum. It is from the burned gas which must be vented outside or you would die from CO poisoning.
"My dad was the most feared furnace fighter in Northern Indiana."
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| | jfevans
| "Re(4):Honeywell 90+ problem (I think)" , posted Wed 5 Nov 18:36
got it, thanks for the help, always good to learn something new
jeff
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