Good Evening,

So I'm having an issue with my Heil Furnace for the last week. Came home from work and noticed the house was unusually cool, looked at the Thermostat and it was set at 18C and it was calling for heat since the House was at 16C.

So I took a trip down stairs and the Exhaust blower Fan was running, but nothing else was. No burners, main Fan, nothing. I did not smell gas or anything.

I grabbed my handy Fluke DMM, and tested the sensors I replaced back in Nov (Flame Role out sensors, two of them since they were showing signs of rust), and I tested another sensor below the Exhaust fan that sticks into the furnace sheet metal, they all tested OK. When I test the sensors, I unplug both wires and use the continuity setting.

I then did some searching, and people say test the Pressure switch, the funny looking sensor with a tube and some wires. Apparently when the furnace is off, the switch is open, and when the furnace starts, it slowly closes. And that is what mine does. It takes about 5 seconds, and I confirmed using continuity, Ohms and Voltage. The pressure switch closes and there is hardly any voltage drop across the two terminals.

Before the pressure switch, are two sensors that look a bit like the Flame outs, but are just called Aux Limit on the Schematic, and are in series with the Pressure Switch. They are attached to the main Blower Fan/motor and are hard to get to, but I can get to their wires easily from the control board. These sensors tested fine.

So I had a look at the flame sensor and the ignitor, was a PAIN to get to, but pulled them both because they are on the same metal mount bracket , and since they were never cleaned since we moved in (~5 years) I just spent the $75.00 and bought a new one. I installed it, and when it was in place, tested the ignitor with the continuity tester and tested okay. I just wanted to make sure I didn't damage it when putting it in.

After all that, still the same issue.

So I took voltage readings on my Gas Valve, it has a wire for the Flame Sensor and Ignitor but 4 additional wires for power and sensors. Two wires, white and black, bring power to the unit and there is 29.5V there (the schematic says it's supposed to be 24V, but it's 29.5V). The Blue wire which comes in from the Pressure sensor and other sensors, is 29.5V, and then there is an orange wire that reads about 300mv.

So I'm not sure if the control board is bad, I do hear some faint clicking of the relays when I turn the furnace power switch on, but I could swear the clicking was louder when I was working on the furnace in Nov. The problem then was the Thermostat was bad, I installed an electronic one and all is good was working great since then until now. But if the control board was bad, there shouldn't be any power to the Gas controller? It seems to be getting power.

To call for heat, I have a skinny wire on the board shorting out W and R. The electronic Thermostat is pulled off the wall anyways right now.

My Control board is ST9120C 4040 HQ1011179HW

My Gas controller is SV9501M 2056

I don't have any documentation for the furnace, just know it's a Heil.

Any help would be appreciated!

Thank you,
George

 

Welcome to the forums.

I just replied to your transformer question.

The SV in the gas valve stands for Honeywell's Smart Valve. That valve is a combination valve that operates the main burner as well as the pilot. That furnace uses an intermittent spark ignition pilot light. You need to restart the furnace. Shortly after the inducer starts..... the spark igniter should start and the pilot light should light. Once the pilot is established..... the burner will light.

The smart valves can be problematic and tricky to troubleshoot. Many times the pilot orifice needs to be cleaned.

Here's the troubleshooting and servicing of the SV system.
honeywell//combustion/universal_smart_valve/install.pdf

 

Thank you Pete, I just noticed you replied to my Transformer Question, I thought I would just ask a simple question in the Forum, in case my original Thesis scared anyone away or maybe they fell asleep trying to get through it. Glad you replied.

So, by your link and response you are thinking the Control board is probably ok and the Smart Valve is the culprit?

I read that most things are controlled by relays from the Control board, I was thinking maybe the Draft Inducer was stuck on? Then further reading and trial error seems to indicate that the Exhaust Draft Inducer and the Blower motor and are often confused. I've watched many a video now, where they get to the part I think they are going to talk about, and they are actually talking about the huge Blower Motor that pushes air throughout the house. My furnace isn't getting that far.....

George

 

I call them draft inducer or draft inducer blower and main blower.

You said you can't find the model number of the unit.
Is there a wiring diagram on the back of the blower door ?
A picture of that posted here would be helpful..... How-to-insert-pictures

 

Ok, I took two photos....since it was hard to get details in one pic frame.

 

Those pictures are only 158x280 pixels. I can't see any detail in them. You can shoot up to 1000x1000 pixels and post them.

 

Ya that wasn't very clear, I tried a couple upload tests and didn't get anything better. It seems though I upload a 1MB file and it . The preview isn't 100% accurate. I noticed this system is more forgiving with JPG , so I'll try that .