Rheem Furnace won't ignite

[Greewater_man]

I have a Rheem Furnace, about 15-20 years old. It was running fine and all of a sudden it I don't have any heat.

The sequence is as follows.

1. Put the thermostat in hold temp and set for 75 degrees Which I know if warmer than the house. There is three feet of snow outside!

2. Fan comes on. There is a little click then after about about 15-20 seconds,

another click and the igniter begins to glow. It glows real good and continues for

a brief while and then turns off. I never heard any gas valve open or something to that effect.

I checked the propane tank and it is at 80%. 

There is a large silver capacitor in the box that has some slight corrosion on the

tabs. I cleaned it well and replaced the wire connectors. What does this capacitor

do? Is it for the fan motor?

[hvacdrd]

Looks like the sequence of operation is normal up to the ignitor glowing. After 25-35 seconds after the ignitor starts the gas valve should energize for ignition trial. You will need(and know how to use) a volt meter to proceed. At the gas valve check for 24VAC, keep your meter leads on the two wires at the gas valve until you see the ignitor drop out. If you have 24VAC then bad gas valve, if no 24VAC we will need a wiring diagram to point you further.

[dkpd1581]

While checking the gas valve, also check your outdoor regulator at the tank.  If you have a bad regulator, moisture build up in it, or low ambient temperatures you may find:

1. A frozen regulator which will cause intermittent operation

2. A defective regulator that is sticking or some other internal issue

3. Ambient temps so low that the pressure inside an otherwise semi full tank is insufficient across the regulator or indoor valve and will cause intermittent problems

4. Improper regulator installation (may be position sensitive in how its mounted)

If all else is good, suspect a tripped/open over temperature sensor ahead of the gas valve's 24VAC circuit or bad gas valve.  Check both for continuity through the coil first and then check for 24 VAC to the coil during start up.

To answer your other question, a capacitor helps the indoor blower motor start up and then stays in the circuit to cause it to operate more efficiently (less amp draw = less $$).

Let us know, best of luck.

[Greewater_man]

If I remember correctly. I had some kind of issue before like this. (It was quite a while ago) but the repair man said that sometimes when the power comes on and off a couple of times, it can trip something in the curcuitry and you have to go over and shut the curcuit breaker off and back on to get things to work again. Does that sound like something in a Robert Shaw type ignition system?

I am curious as to the reply about theregulator. There was alot of snow on top of the propane tank. The regulator is buried inside a metal cover but no insulation and the copper tube runs along side the tank to the pipe that goes down into the ground. I would guess that I could very carefully check outside where the gas comes into the house by unscrewing one of the fittings to see if there is flow. (Of course, cigarette smoking is prohibited, ). There is some sort of regular at the tank and one right where it goes into the house.  I will check this out.

[RegUS_PatOff]

[user=44948]Greewater_man[/user] wrote:

... There is three feet of snow outside! ...

Is this a Direct Vent Furnace ?

[Greewater_man]

I am not sure what you mean. It says that it is a induced draft typ gas furnace.

 

[dkpd1581]

Make sure the flue is free of obstructions (especially on the roof) that would keep the unit from starting up - ie snow.

[Greewater_man]

So I checked the gas valve for 24volt at the terminals and didn't appear to see any voltage. Can I put 24volt across the terminals of the gas valve to see if it will function?

Is there any way to check the ignitor unit to see if it is toast? Can I take it to a furnace repair place and have them test it?  How can I tell if it is not something in the other curcuit board that is below it in the box? I have checked most of the little gizmos that appear to look for over temperture. I am assuming that normally closed is what I would want to see. The ignitor unit is a Robert Shaw, model HS780-34PL-308A. The other curcuit board says 695-211 (HSC992-21). It is a Rheem Furnace model number

RGDE-07ELAES Serial# F4591 9318 (4G50304 )75,000BTU . Gas valve # 7A5-A83-003 (24vac - 50amp) 7200DER   1/2 PSI

One other thing is a person emailed me and said to replace the gas ignition control with a Robert Shaw 780-910 uni-kit which  is supposed to have a self diagnostic green LED for troubleshooting.  They say that this unit easily replaces the widest variety of hot surface ignition modules found in the field today. It is supposed to  provide 100% lockout and complete gas shut off it the main burner does not light after the selceted trial for ignition secquence has been completed.

[RegUS_PatOff]

I'm not an HVAC expert, but here's some info

Robert Shaw 780-910 info

 

[jahjahbinks]

damn it sounds like a smart valve . post the valve model no# sv???

[Greewater_man]

Ends up that it was the ignitor module. The wiring diagram for the universal module was a bit vague. Ends up that the two light blue wires for the fan curcuit board went to the valve only and there is no wire on the TR tab. Everything is working ok now. I put 24volts to the valve and it fired off so I put in the ignitor module and figured out the wiring after a bit and all is well. Thanks to everyone for their input.