Furnace

[rlp in Co.]

Well, the transformer came today to replace
the one damaged by 240V. I installed it but
the furnace would not work! This was strange
because I tested the furnace with a varyac
transformer at 24 volts and it worked
perfectly. The new transformer puts out 27
volts, so I thought maybe that was the
problem.
This is what the furnace did. The draft
blower comes on, then the igniter lites the
pilot lite and then the burners don't lite
and the furnace shuts down and gives 6
blinks, pause and one blink. I looked up the
code and it says soft start fail. So then I
tested the flame sensor and it is 18 ohms. I
then tested the voltage on the two blue
wires which I think are for the flame
sensor. Anyway 4.5 volts appeared and walah!
The burners lit up! So I guess the flame
sensor is bad? Anyway I left the voltmeter
hooked up so the furnace would work and
ordered a new igniter and senser, $24! Why
didn't the furnace flash the code for a
flame sensor? Did the extra voltage burn out
the flame sensor? Why does the furnace work
with the volt meter hooked up? It's crazy!!!
I have to wait till Jan. 15 for the igniter
and senser! Will the extra voltage burn out
the new sensor?

 

[M-MAN]

Your voltage is fine. Most are 26 out of the box. What you are doing is using your meter as a jumper to bypass the flame sensor. Using a jumper is standard procedure to test it or even run it a day or two in an emergency. It isn't ok to leave any safety sensor bypassed for a few weeks. Somewhere within driving distance there's a hvac supply house or a hvac contractor that will sell you a new sensor.

 

[showcrop]

2X what M-MAN posted. Go today and pick one up. Keep the Amazon sensor for a back-up.

 

[MarkB_MI]

What sort of meter are you using? A digital multimeter should have a high enough input impedance that it won't effect the furnace circuitry. But an analog meter or a very crappy digital meter could. Another possibility is your meter probes are causing something to contact that otherwise is open.

What kind of flame sensor is it? If it's just a steel electrode, clean it up with sandpaper and it will probably work. If it's an optical sensor, wipe the dust off its lens.

It is ridiculous to wait nearly a month for an igniter and flame sensor. Find another source that has them in stock. You can keep the ones you've already ordered as spares. I've had very good luck ordering furnace parts from both <a href=https://www.supplyhouse.com>supplyhouse.com</a> and <a href=https://repairclinic.com>repairclinic.com</a>.

The flame sensor problem is most likely a coincidence. You probably would have had to fix it even if the transformer hadn't blown out.

 

[da.bees]

More than half of supply houses around DFW refuses to sell to anyone other than contractors. Trade organizations have made them think it's illegal selling to anyone without license.

 

[MarkB_MI]

> More than half of supply houses around DFW refuses to sell to anyone other than contractors. Trade organizations have made them think it's illegal selling to anyone without license.

That's a real problem around here, too. Most of the wholesalers used to sell to homeowners if you came in the door, but they've gotten to be sticklers. As a result, I buy almost all of my HVAC supplies online. And once the contractors figure out they can buy online for less and get stuff a day later, those supply houses that only sell to contractors will go belly up. Some already have.

There's a place about 45 minutes away from me called repairclinic.com. Although they're mainly an online store they have a storefront that's open seven days a week. They've saved the day for me many times when a furnace quit on the weekend.

 

[Crazy Horse]

Mark: Flame sensors caused us years and years of grief with our mid-efficiency furnace until we got a new high efficiency furnace a few years back. Incidentlly, you cannot buy a mid-efficiency furnace anymore up here unless you find one on the black market. You mentioned sandpaper ..... one furnace tech gave me an lesson on how to service them (removal, cleaning, installation) and he said 'sandpaper' generally but something very fine like wet/dry grit level to clean them. Or one of those plastic or fibrous scrub pads, etc. Perhaps regular sandpaper left the surface scratched too deeply and ended up being more susceptible to corrosion buildup, not sure. Nippy up here this morning, -33C or -27F .... take your pick. I'm glad the furnace is working.

 

[MarkB_MI]

> You mentioned sandpaper ..... one furnace tech gave me an lesson on how to service them (removal, cleaning, installation) and he said 'sandpaper' generally but something very fine like wet/dry grit level to clean them. Or one of those plastic or fibrous scrub pads, etc. Perhaps regular sandpaper left the surface scratched too deeply and ended up being more susceptible to corrosion buildup, not sure.

That's a good point. I was assuming he'd replace the sensor once the new one came in, but yes, you should use something fairly fine. I think those sensors are stainless steel.

 

[Hobo,NC]

I am gonna throw ya a bone that saved me as mine was acting about the same.

There is a vent valve on top of the gas regulator had stuck/stopped up it gave a few HVAC repair men a fit. I called my NG man he came out screwed the vent off the regulator and put a new on in I was back in business.

 

[BarnyardEngineering]

(quoted from post at 05:38:03 12/21/22) More than half of supply houses around DFW refuses to sell to anyone other than contractors. Trade organizations have made them think it's illegal selling to anyone without license.

I don't think it's legal threats as it is financially motivated.

That and the clear benefits of not having to deal with the "I know what I'm doing" types (who really don't).

 

[wore out]

Consider this... when the transformer primary was fed 240 Volts the output of it's secondary to the electronics would have been 50 to 55 Volts during the seconds (or more) it took for the thermal fuse inside the transformer to get heated up enough to melt and open!

Dunno if I would want to trust the electronics to control a GAS furnace safely after that event!

That being said, what is the make and model of the furnace, and what is the control system, does it have a separate circuit board, or is it a "smart'' valve with electronics inside the valve?

Hot surface ignition or spark?

What is the make and part number of the ''flame sensor''?

(''Two blue wires'' makes me think it is the hot surface ''glow plug itself''.)

When you were reading voltage at the ''flame sensor'' was the meter set to AC volts or DC Volts?

 

[ss55]

Is the flame sensor an old fashion thermocouple? Any ACE Hardware store and big box home store will have them in stock in different lengths. Measure your old one or better yet bring it along when you buy a new one.

 

[MarkB_MI]

> Is the flame sensor an old fashion thermocouple?

Probably not, based on his description.

 

[Richard G.]

All that electronic stuff is why I do not and never will have a furnace.
Wood heat here with gas logs as a backup.
3000 sq ft to heat and we are very comfortable.
I built the house and the exterior walls are about 8 inches thick.

 

[DoubleO7]

(quoted from post at 10:55:15 12/21/22)

(quoted from post at 05:38:03 12/21/22) More than half of supply houses around DFW refuses to sell to anyone other than contractors. Trade organizations have made them think it's illegal selling to anyone without license.

I don't think it's legal threats as it is financially motivated.

That and the clear benefits of not having to deal with the "I know what I'm doing" types (who really don't).

That along with maybe a cost of liability insurance selling to those that are not qualified.

 

[John T]

You ask Is the flame sensor an old fashion thermocouple?

I doubt it and suspect an electronic Flame Sensor detects the flame versus the old thermocouple system. They sense and operate using a small millivolt signal which connects to an elec circuit board that turns gas valves on and off IF ITS THE KIND IM GUESSING IT IS ??? NO Warranty

John T NOT an HVAC Tech or an expert maybe one will come along and give the OP qualified advise and answers ?? Hope so we will see

 

[M-MAN]

The supply houses I use don't like to sell to walk-ins either but if you're polite they will sell you the small stuff. The bigger contractors here will sell parts also as we have to drive an hour to the closest supply house.

 

[showcrop]

(quoted from post at 08:10:25 12/21/22) All that electronic stuff is why I do not and never will have a furnace.
Wood heat here with gas logs as a backup.
3000 sq ft to heat and we are very comfortable.
I built the house and the exterior walls are about 8 inches thick.

If you don't want a furnace you could always install a boiler with baseboard heat. The as logs can get very expensive when you are down for a month or two and can't carry the wood.

 

[Frankmn]

the two blue wires are probably a roll out switch. a jumper wire closes the switch and opens the gas valve. flame sensor generally has one wire and is just a stainless steel rod.

 

[rlp in Co.]

I've seen pictures of your house. Nice!!!

 

[rlp in Co.]

I have not taken it out yet; it doesn't appear to be a thermocouple. I repaired a thermocouple for my oven. The appliance place didn't have one with long enough wires. I got to looking at the old one and I wondered if I welded it back together with a torch; if it would work? So I did and it has been working for a long time now!

 

[Gary Reif]

I've had an issue similar to yours, and all I did was use steel wool and lightly cleaned the soot off the flame senser and all was well. UMMV

 

[rlp in Co.]

It is a honeywell valve and if I remember
sv9541. The voltage was 4.5 DC. It has a
control board but I think the flame sensor
circuit might be in the gas valve, because
that's where the three wires connect. Two
blues and a black. I didn't test the black
wire because the furnace started when I
tested the voltage on the two blue wires.

 

[rlp in Co.]

It has a glow plug igniter and like I said,
that works good, and lites the pilot lite,

 

[rlp in Co.]

The regulator on my propane tank? I think
that is good because my stove works
normally.

 

[Stan Coryell]

If you have a flame sensor, not a thermocouple, they generate current when heated (miliamps). The only way to test them is with an amp meter. I can tell you they don't go bad. They can get damaged, broken wire. They also get corroded. Use the back of a knife to scrape the flame sensor. Also check all the grounds, the flame sensor only has one wire, it needs to be grounded to the frame as well. It's possible the control board was able to pick up a ground through your volt meter.

I would guess you have a ground issue.

Pictures and a schematic would help. The only voltage you should have is 24VAC and 120VAc (nominal).

 

[rlp in Co.]

I am using a harbour freight digital meter. I know that the impedance is low on this meter which is probably why the furnace started working. I have an analog meter that has a very high impedance but I hardly ever use it anymore because this meter us so handy! I have at least ten of these that harbour freight gave me; what a great company!!!!
It is also great for electronic circuits because it has ranges that can measure ohms without turning on transistors!

 

[wore out]

(quoted from post at 12:08:25 12/21/22) It is a honeywell valve and if I remember
sv9541. The voltage was 4.5 DC. It has a
control board but I think the flame sensor
circuit might be in the gas valve, because
that's where the three wires connect. Two
blues and a black. I didn't test the black
wire because the furnace started when I
tested the voltage on the two blue wires.

OK, so you have a Honeywell/Resideo ''Smart Valve''.

Would be good to have the complete part number, some older units may have not been very reliable/safe, and are replaced by an updated unit with a new part number.

The two blue wires are the from the hot surface element, which operates on 24 VAC, the black wire is from the flame rod/flame sensor.

http://s3.supplyhouse.com/manuals/1249544859835/Honeywell_SV9501_InstallGuide.pdf

Honeywell Smart Valve info.

 

[rlp in Co.]

I suspect the high 27V might be the issue. The furnace worked good when I tested it with my vary AC transformer at 24 V. A varyac transformer is a autotransformer with only one winding and a variable tap at any place on the winding. The tap can vary from 0 to 120 V or 0 to 240 V! I'm going to test the furnace again at 24 V, when I get time, and see what happens!

 

[Stan Coryell]

The valve model number helps.

The gas valve didn't know the pilot lit
(problem with flame sensor or flamesensor
circuit) so the smart valve locked out.
This lock out is the code flashing. It's
possible there is a problem with the valve
also, although I don't think so. The valve
wouldn't have opened when you connected
your meter to it. Manufacturers are pretty
particular about NOT allowing the gas
valve to open until ALL the safety devices
are proved. There is no simple way to
trick a flame sensor since it generates
current.

There is a flow chart in the gas valve
manual that describes the Order of
Operations.

1st,
Disconnect the flame sensor wire from the
valve, place your micro amp meter in
series with the valve and sensor. Let the heater cycle. You
should read between 0.5 (yes point 5) and
10 micro amps withthe pilot lit. I don't really know what it
should be. Honeywell may have it in the
instructions.

If you have less than 0.5, the main valve
will not open. I would be suspicious of a
ground or dirt issue at anything less than
4 or 5 (5, not point 5) micro ohms.

If less than 0.5,
Clean flame sensor with the back of a
knife and check grounds. Re check amps.

If amps are more than 0.5 and the main
valve won't open,
Valve is likely toast. (Your electrical
schematic should verify this)


I would not start changing parts until I
was pretty confident in what was wrong.

 

[Stan Coryell]

It doesn't matter if it's 22 VAC or 28 VAC. I would expect to measure 26 or 27 VAC. Remember thermostat wire length and load will lower the voltage. Years ago thermostats had heat anticipators (sp?) to compensate for wire length. They went away with mercury.

As a side note, most modern 2 stage units no longer use a 2 stage thermostat. The stages are controlled by an algorithm. For the past 25? Years we have not had standing pilots. Why do heaters have to have a smart valve? The valve was dumb and the controls were smart. Now we have a gas valve costing twice as much as before with ZERO additional safety factors. (I'm sure the control boards still cist the same)

 

[rlp in Co.]

Thanks for that link! The two blue wires are the igniter, but the igniter works perfectly! I think I have a ground issue somewhere and something grounds thru the meter! If the flame sensor only has one wire, it must ground thru the frame or the igniter wires.

 

[rlp in Co.]

Too late, I already fired the parts cannon at it! Ha! I will try your suggestions. Maybe clean the flame sensor and see if it is grounded.

 

[rlp in Co.]

The old valves worked good and if the pilot blew out, the burner wouldn't lite! The problem was, the pilot lite had to be on all the time and wasted gas and caused the furnace and pipes to rust because the pilot lite didn't create enough heat to keep the firing chamber and the pipes warm. The water formed from the pilot lite would therefore condense on the walls of the firing chamber and pipes and rust them out! The exhaust pipes on my Dads furnace rusted out for this reason and because he left the pilot lite on all summer long!

 

[rlp in Co.]

I wish you would have told me this before I ordered a new sensor! Ha!

 

[rlp in Co.]

I can't buy airconditioner parts anymore either! Now you have to pay a company a hundred dollars an hour to fix anything anymore! How long before the Nazi commies ban auto parts?

 

[MarkB_MI]

> Thanks for that link! The two blue wires are the igniter, but the igniter works perfectly! I think I have a ground issue somewhere and something grounds thru the meter! If the flame sensor only has one wire, it must ground thru the frame or the igniter wires.

The flame sensor works on the principle that flames conduct electricity, but air and natural gas do not. The sensor circuit grounds through the pilot burner. Clean up that sensor and I'm 99 percent certain it will work. It's a good idea to clean it up annually.

 

[showcrop]

(quoted from post at 15:00:01 12/21/22) I can't buy airconditioner parts anymore either! Now you have to pay a company a hundred dollars an hour to fix anything anymore! How long before the Nazi commies ban auto parts?

Nazis and commies are generally considered to be opposites. Nazis aren't a division of communists.

 

[Richard G.]

Thank you Sir.

 

[wore out]

(quoted from post at 15:31:23 12/21/22)

''The sensor circuit grounds through the pilot burner.''

Yes, somewhere in the official Honeywell info it is mentioned the the pilot gas supply metal tubing is considered the ''ground connection'' between the flame sensor and the ''Smart'' gas valve.

 

[Stan Coryell]

I don't think any residential heating equipment has had standing pilots for 30 years. They have used a hot surface igniter since the early 90's.

I doubt the standing pilot rotted the flue pipe. I'd imagine it had more to do with draft and a damp basement. A dry basement and a properly sized flue (with a cap) should solve the condensation problem. New Jersey tried to solve this by requiring a 80% AFUE 40 kbtu water heater to have a 4 flue. As far as I know, this is the only such requirement in the US. The rest are 3.

 

[Stan Coryell]

There is no simple way to jump a flame sensor. It isn't in series with 24VAC. It produces a small current. The only ones I have had bad had physical damage, broken wire.

 

[Geo-TH,In]

Before high efficiency furnaces, I was a HVAC repairman.
My theory today is KISS. KEEP IT SIMPLE.

Today's furnaces and heat pumps are more efficient and save you money until you have to call a repairman. Then all your savings go out the window when you have to pay for a service call and parts.
Furnaces and heat pumps only breakdown on holidays, weekends, and the coldest day of the winter when HVAC repairmen are working their butts off.

In 1985 I rebuilt a house. Yes rebuilt! There was an explosion inside the house. The house is next door.
I made this house super insulated

The 850 ft house has a full basement.
I can cool the house using a 6000 btu window AC.
I put simple maintenance free electric baseboard heat in every room. Tenants only use one 8 ft baseboard heater in the living room to heat this house. In the past 37 years I haven't repaired one baseboard heater, no service calls.
Because I invested in over insulating this house. Tenants can't believe how easy it is to heat and cool. I have no worries about repairing a furnace when I'm in Florida in the winter. KISS works for me.
I have turned my house into a super insulated house.
It took me 5 years to do it. Central air and electric baseboard in every room.
FORGET HIGH TECH. Super insulate and forget furnaces.

 

[rlp in Co.]

To heat with electricity here, will cost a third more money, and when the electricity goes out, like it always does, you freeze your but off! Several years ago, it was off for 7 days! With gas, you can heat your house with the kitchen stove!!!

 

[Geo-TH,In]

Each to their own. It's your money. Your repair bills. Your money to replace the high tech furnaces and heat pumps.
Good luck with your furnace.

You could still use electric heat and heat with your gas range in the event electricity goes out..

I enjoy not getting a call from a tenant in the middle of the night, I don't have HEAT and my water pipes are frozen.

Factor in the repairing frozen pipes.

Nothing to repair or replace. No annual inspections. No motors to go out. No controls to replace. No air filters. No holes in the heat exchanger.

Peace of mind is worth something..