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jacob 01-04-2008 05:57 AM

marsh furnance
Help I'm looking for any info and help on a Marsh wall furnance,about 20-25 years old,model no NFO774.Can someone help me?

jacob 01-04-2008 02:48 PM

Realy need some help here,does anyone know of this brand of furnance and where I can find help?

redline 01-04-2008 03:24 PM

What is wrong with it?

electric or gas?

bigMikeB 01-04-2008 04:01 PM

If it hit 20yrs, replace it, the life you save my be your own.

jacob 01-04-2008 05:03 PM

This is a gas wall furnance.The problems are that the pilot is on but the burner will not come on.There is a high limit in the top that is not resetting right.Please help.

bigMikeB 01-04-2008 05:06 PM

Have you removed the high limit? If thats the problem they are easy to buy and replace.

jacob 01-05-2008 05:13 AM

I took the wires off the high limit and put them together and it still would not light.Is there any way to check the burner or gas valve? Thank you so much for your time.

bigMikeB 01-05-2008 07:06 AM

Yes there is a way to check it out, first off you need a volt-ohm meter, and a schematic of the control circuit. Secondly don't guess or assume you know the problem without properly checking through the control circuit. Lastly it makes little sense to put big repair money in a unit that is 20 plus years old on an item that doesn't last much longer than that.

jacob 01-05-2008 11:50 AM

No schematic of the control circuit,that's what I'm looking for,any info on how to troubleshoot this thing.You are probably right about not fixing this old heater and just replacing it,and that's what I'll do for next winter,but we are about thru with winter and I would like to get this thing going to finish off this season.Hope some can help me.How does the circuit ofn a wall heater usualy run?Like from line power to transformer to thermostat to........? where..

bigMikeB 01-05-2008 09:14 PM

Power from the transformer runs to the t-stat and the stat sends power to the gas valve circuit through the limit switches. No power to the valve when the stat is made and one of your limits is open.

jacob 01-06-2008 05:35 AM

Thank you so much for the info.I'm going to try to make this thing last for the rest of the winter,then I'll replace it.Thanks to all of you guys that help us so much.

jonrotten 01-21-2008 10:42 AM

I have a Marsh wall furnace that did the same thing some years back. Seems that the wire used in it was much like lamp cord and it developed enough resistance at a bend to keep it from operating the gas valve. It still read continuity but had a high resistance value. Once I located the high resistance area by probing with a dvom, I cut it out (approx 2") and wire nutted the 2 ends together. It was a great heater til removed last fall for central installation. Still have it in the shed for parts.

jacob 01-22-2008 05:24 AM

marsh furnance
Thanks for your reply and very intersting troubleshooting effort.I'm going to go and check as you did and look for high restiance in the wiring.Do you know if any repair info or manuals exist for this unit.Thank you again for the very good insight on this problem.

bigMikeB 01-22-2008 05:09 PM

Repair/ engineering manuals are usually only available for @10 years, only 7 is required by law. Maybe you can find one on an antique heater website/forum.

jacob 01-23-2008 05:12 AM

thank you for your reply.I'll look for some of these websites

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