Ruud Furnace stumps Pros

[hamish]

I look after an elderly widow (84) who has had a lot of trouble with her 1990 Ruud UGDA- 10ECBEA HIS furnace. I am not in the HVAC trade, neither am I a DIY or a DYI I reside near Vancouver British Columbia Canada. I have hired pro contractors to do the job, but after three different contractors, the latest solution suggested is to replace the furnace. Considerable dollars have already been spent $1700 in repairs with reputable companies.
Parts Replaced:
Nordyne HIS 903758 Mar. 31, 2004
Millivolt thermostat Oct. 01, 2004
Main Gas Valve Honeywell VR8Z45M2530 Dec. 30, 2004
Relay switch for control Dec. 30, 2004
Time Delay control Jan. 31, 2005
Control module (board) Feb. 2005
Control module (board) Mar. 2005

After the control module has been reset (by power off) the furnace will cycle through the start up sequence and fire the burners, blow heat, burners shut down, relight and blow heat and shut down and fault with no restart unless the power to the furnace is cut and the control module reset. This has stumped the contractors who have tried diligently to fix the problem.

In desperation I brought over a electronic technician friend of mine to take some measurements, he has 25yrs in circuit boards. When the control module faulted it was intermittent, sometimes it would kick 24v to the gas valve but not open it, or at other times no volts were sent to the gas valve. This control module has been replaced twice in two months and it appears to be faulty again. Should I have this replaced again? Any suggestions other than a new furnace.

Control Module: Robertshaw HS780 34NL-306A Part # 100-00812-31

[mike d373]

Why would they put a millivolt t-stat on a 24v system?

[hamish]

Not sure why the tech did that, I don't even know were it’s located. I think the tech was trying in desperation. The company he works for sent a tech from another company that was supposedly a Ruud expert. That is when the second control module was put in. The tech that gave up on this repair suggested that a flame rod sensor be put in??

[mike d373]

Originally posted by hamish
I
After the control module has been reset (by power off) the furnace will cycle through the start up sequence and fire the burners, blow heat, burners shut down, relight and blow heat and shut down and fault with no restart unless the power to the furnace is cut and the control module reset. This has stumped the contractors who have tried diligently to fix the problem.


Control Module: Robertshaw HS780 34NL-306A Part # 100-00812-31

What is the fault code on the circuit board?

[hamish]

The circut board has no fault code LEDs on it.

[NormChris]

There is no furnace problem that a real professional heating and cooling technician can't properly troubleshoot given the time and proper instrumentation. If you had a true professional technician out, the problem would have been taken care of already.

Call another service company. Have the technician contact the factory's tech services department if necessary. The problem can be solved.

[hamish]

Thanks for the encouragement that the problem can be solved. My elderly friend is quite distraught over this and feels that she needs to buy a new furnace. Does the symptoms I describe sound like the control module again? If so I think it must be under warranty and maybe I should get the tech back to replace it.

[MechAcc]

Have the technicians troubleshoot by jumpering the R to W terminals at the furnace? That would eliminate the thermostat and thermostat wiring as the source of problem.

[NormChris]

There is no way for any of us to troubleshoot the problem without actually being there. If the others who were there could not determine the cause we are at an even greater disadvantage.

It could be the control and it may not be. The control monitors safeties and other functions. There are inputs to the control from all sorts of sensors and control components. The control is the brain of the system. It will shut down if any of the sensors detect a problem. So, it could be that the control is doing exactly what it is supposed to do and the problem is elsewhere. It could also be the control itself. If I were there I could find the problem.

You need to find a real professional to solve the problem. One who knows what he is doing and will not give up easily.

[hamish]

Thanks for your advice. It's hard to find a real professional, when you call the ones listed they all say That they are professionals. I have tried 3 now with no luck yet. Is there some sort of testing equipment that only a true professional would have that I could maybe ask if they have to help seperate the pros from the wanabees?

[NormChris]

I see that you are located in Mission BC, Canada. Perhaps someone on this board will read this who runs service in your area and may be willing to work with you.

Norm

[hamish]

Good idea Norm. Thanks for your help.

[beenthere]

Have check the limits, and the pressure switch also.

Your electronics friend may know electronics, but you need to know the sequence of operation when trouble shooting.

And get rid of that millivolt t stat.