1973 DuoTherm Furnace Model#75003 Help

Questions about repairs and parts for other brands of furnaces and air conditioners. Please note that our speciality is Coleman and Nordyne products, so our knowledge of other brands may be limited.

Moderators: Greg, Mark

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locobear
Posts: 1
Joined: Mon Feb 16, 2009 4:38 pm

Hello to all, am having a problem with furnace burning too hot even with inlet gas line pressure at 11.0 WC inches and with gas valve outlet pressure set to same for LP gas. The place I purchased a replacement valve from insists that it is the correct valve(RobertShaw 720-472 24 volt step-opening combination gas valve) to replace the original part#H-3226 The air intake is clear, registers are not blocked, as far as I can tell flue is clear and I vacuumed inside of burner box-this is all that I can access to clear soot out. The only way I can get it to burn what I think is properly is by turning the supply gas shut-off valve about halfway closed-this results in the WC inches manometer reading 3.5-yes I have turned over the gas converter on valve for LP conversion. Furnace info plate says 65,000 btu input-replacement gas valve control instructions say 15,000 min to 280,000 max. I assume this to mean anything which falls between this limits is ok. I'm wondering if this is a case of the model made for manufactured home being slightly different and a "universal" gas valve not being the right remedy. Also if it is possible for there to be soot where I can't get to it, can see heat coming out of top of flue on roof so I am assuming it is clear. Any help/suggestions would be greatly appreciated.
Thank you, Sean
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Robert
Moderator
Posts: 6413
Joined: Wed Feb 28, 2007 12:07 am
Location: Tennessee

Hi Sean,

It would be best to call an hvac tech to diagnose and resolve this issue.


With it being an older furnace and running on LP, not something to DIY on at this point.


Call Mark toll free at 1-877-263-7860 and see if he can confirm if you have correct gas valve.


Thanks,
Robert
Some people are Humbly Grateful, while some are Grumbly Hateful.................... Which one are you ?
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