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BOSCH Vision 500 Gas (NG) Dryer Model #WTVC6530UC/11 - igniter won't light, rapid clicking sound

KenBradley

Premium Member
Joined
Nov 20, 2010
Messages
13
Location
CT
Model Number
WTVC6530UC/11
Brand
Bosch
Age
6-10 years
Have a Bosch Natural Gas Dryer, Model #WTVC6530UC/11. NG Burner Assy won't light not will the igniter glow. Was working intermittently until last week, now won't light or glow to start at all. Dryer powers up and tumbles on all modes. . . . just will not heat up.
When it WAS heating, it would often click rapidly, like an electrical switch/relay cycling like 5-10 times per second. It almost sounded like a bucket of BB's rattling around from upstairs. It was definitly an electrical cycling sound. Would last maybe 2-4 sec. max and stop.
- took apart and checked for lint blockages in pipe and exhaust - all clean
- thoroughly cleaned lint filter, lint filter area, and cleaned off moisture sensor with alcohol.
- this exact same issue cropped up about 2 years ago. Ended up replacing the gas valve/burner assy #00497969 and igniter #00491648 - this solved the problem of the dryer not heating. But, the rapid electrical cycling during operation would still happen randomly during operation. The dryer would continue to work. . . . but that cycling noise just wasn't right.
- started to happen more often lately. Dryer wouldn't work for a few loads, then would randomly start drying/heating again. Tried unplugging the unit. . . .sometimes that would help, but don't know if it was simply coincidence. Now, the dryer hasn't heated up in over a week. Have tried every cycle and trick, but can't get it to light off.
- 2 years ago, had checked and tried jumpering all sensors - lint sensor, moisture sensor, hi-limit sensor, flame sensor, NTC, but was unable to get dryer to work when I did that, so replaced gas valve and igniter, which solved the immediate issue of dryer not heating.

Has anyone ever experienced this rapid electrical cycling noise before? Assume it's a sensor sending conflicting signals and rapidly changing from open-to-closed, but perhaps it happened so fast, the burners stayed lit?

What sensor or device would cause such a noise?

Could this "bad" sensor have caused the gas valve to fail again?

I thought this dryer had a diagnostic mode. I would think with all of these sensors and built-in diagnostics it could tell you what failed, or at least have provided an "error code" when the gas valve won't light. Why does it have this diagnostic system, if it can't even tell it's not operating/heating up?

Does anyone know how to access the diagnostics on the machine, and how I could check for a possible failed part or error code??

Are there any "common problems" on the gas dryers that I should check for?

I don't want to blindly purchase a new gas valve or igniter like I did last time, as I feel they should be OK since they were both recently replaced.

Any thoughts? Suggestions? Troubleshooting tips?
All modes work (tumble) as they should. . . . dryer just won't heat up.
I haven't tried jumpering or disconnecting any of the sensors this time around. Was looking for advice before diving in again.

I know how to take the entire machine apart, and have no issue getting to any of the components.

Thank you in advance for any assistance you can provide.
 

rickgburton

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KenBradley said:
checked and tried jumpering all sensors - lint sensor, moisture sensor, hi-limit sensor, flame sensor, NTC,
FWIW: Bad idea. The only parts you can short (jump) is the cycling thermostat and the high limit thermostat. The flame sensor is normally shorted. That's how it works. Sensors or NTC thermistors are variable resistors that change value with temperature. Shorting the wrong thermistor could damage any control boards.

The problem is with the split coils on the gas valve. Bosch doesn't sell the coils separately but I will link you to a set that will work. If you have 120 VAC going to the gas valve, here's how it works;

Neither the hold coil nor the assist coil alone is strong enough to open the valve. The combined magnetic action of both coils is needed. Once the valve is open, however, the hold coil can hold it open by itself.
When voltage is applied to the gas valve, a circuit is completed from V1 to the ignitor, and through the flame switchr to V3. Simultaneously, the hold coil is energized, and the assist coil is energized through the flame switch. This means the ignitor is heating and valve #1 is open. No gas flows, however, until No. 2 valve also opens.

split coil circuit-1.jpg

There's no voltage going to the primary coil because electricity takes the path of least resistance (flame switch). When the igniter temperature is sufficient to open the flame switch contacts the primary coil is energized opening valve #2. Magnetism created by the hold coil is sufficient to hold valve #1 open. The primary coil has less resistance than the assist coil and electricity takes the path of least resistance.


split coil circuit-2.jpg

These will work:

 

KenBradley

Premium Member
Joined
Nov 20, 2010
Messages
13
Location
CT
Hi Rick - Thanks for the great info. I had some info from a portion of the manual a few years back, and can't remember exactly which switches I tried disconnecting or jumping (it actually wasn't all of them). Might have been only the lint sensor and the hi-limit switch at the time??? Anyway, the dryer has been working fine for the last 2 years, except for that circuit cycling noise (and that was happening randomly before the first gas valve replacement).

1) Anyway, what if the ignitor isn't even glowing?
Is there anything in the "start up" circuit that would prevent the ignitor from glowing at all (besides a bad ignitor)? Is there a switch or sensor that prevents voltage from going to the ignitor?

2) What do you think that relay/cycling noise could be? What could cycle fast enough to create a noisy buzzing that you could hear loudly from upstairs? Sounded like noise originating from bottom of dryer (maybe), not from the control panel at the top. Only lasted a few seconds when it happened. Would sometimes happen multiple times throughout a cycle, but was always random/intermittent. Sometimes wouldn't happen for days or weeks. It isn't a mechanical/bearing noise, it's definitely electric, and I honestly believe it has something to do with the machine not working consistently. Could the noise be the coils in the gas valves? Could a "bad" signal from somewhere or a rapidly failing/changing sensor cause anything inside the machine to behave like that? Happened with original gas valve and the replacement one, so doubt it's the gas valve coils themselves. Could it be a signal going to the coils? Other thoughts?

3) Is there some way to get the built-in diagnostics to provide any type of error code that could assist with troubleshooting?? I have NEVER had any lights go on in the past except the "lint sensor". Have never rec'd any type of error code on the display.

Appreciate anything you could tell me and wonder if the ignitor not lighting at all or the buzzing noise (when in the middle of a normal heated cycle) tells you anything more?
 

rickgburton

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Let's do one problem at a time. There's a good chance when the heating problem is fixed the noise will cease. There is most likely a way to get into the diagnostics but I don't have any information on Bosch machines. Locate your tech sheet if it's still there. That will have the info you're looking for along with error codes. You should be able to figure out the igniter with the information I gave you.
 

KenBradley

Premium Member
Joined
Nov 20, 2010
Messages
13
Location
CT
Let's do one problem at a time. There's a good chance when the heating problem is fixed the noise will cease. There is most likely a way to get into the diagnostics but I don't have any information on Bosch machines. Locate your tech sheet if it's still there. That will have the info you're looking for along with error codes. You should be able to figure out the igniter with the information I gave you.
Hi Rick -
Replaced the coils back in Aug. Dryer started right up. However, occasionally still had days were I had rapid cycling of the coils during operation (intermittent). Sometimes had to shut off dryer and re-start. I had random days that dryer would not heat, would unplug dryer and try again next day. Have been able to use it "most" every day, but stopped working 2 days ago, and will not light. I have a feeling it is one of the sensors giving the coils false signals. Not sure how to determine which one. The dryer has "diagnostics", but doesn't seem to be able to provide any useful information or error codes when the dryer won't heat (you would think this would be the most obvious application for the diagnostic system??). I'll e-mail you a copy of the portion of the factory manual I found online, maybe you can provide some additional guidance on figuring out what sensor is causing the issue. Not sure if I need to replace the coils again now???? But there's obviously a 2nd issue causing the coils to fail prematurely. Thank you.
 

rickgburton

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I have a feeling it is one of the sensors giving the coils false signals.
There's no "false signals" because there's no signals only voltage. There's a metal sleeve on the valve shaft that the hold coil and assist coil go over. Sometimes that metal sleeve gets stuck inside the old coil and gets thrown away. If that happens the valve won't open all the time and it makes a chattering noise. Check that first
Sleeve Gas Valve.jpg
 

KenBradley

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Joined
Nov 20, 2010
Messages
13
Location
CT
There's no "false signals" because there's no signals only voltage. There's a metal sleeve on the valve shaft that the hold coil and assist coil go over. Sometimes that metal sleeve gets stuck inside the old coil and gets thrown away. If that happens the valve won't open all the time and it makes a chattering noise. Check that first
View attachment 46474
I remember that sleeve being there for sure when I swapped out the coils in Aug. The gas valve fired right up and has been working OK for nearly 3 months. However, intermittently, something is signalling the coil and it rapidly opens/closes (sounds like a bucket of screws being vibrated). When it starts this, the valve sometimes keeps working and finishing the cycle, but every so often it causes the coil to stop working or to not trigger the valve the next time it is supposed to start. Wires are all in great condition, connectors look good and are tight, nothing is pinched. Just seems to me that something must be telling the coils to shut down, but signal/voltage isn't consistent and it rapidly cycles. I have e-mailed you the diagnostic/service manual excerpts I have. Thank you!
 

rickgburton

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Let's break it down to two circuits. Everything on this side of the gas valve connector is the dryer circuit. Everything after the connector is the heat circuit. If the dryer circuit is supplying a constant 120 VAC to the heat circuit we can eliminate everything in the dryer circuit. The igniter is working so eliminate that. The flame switch could be causing the problem. It's easy to check with your meter. @ room temperature it should have less than 1Ω or should read closed. Measure the resistance of the coils. If you got the coils through the link I gave you you can exchange them.
L-gas valve 1 & 2.jpg
 

KenBradley

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- I will check resistance of both coils late tonight.
- When the gas valve "acts up", the igniter will NOT glow. When it decides to work as designed, the igniter will glow and the valve will light off. The igniter never glows at the same time that the gas valve will not fire. Something upstream is obviously preventing igniter to not glow. Igniter is fine (and I actually replaced it in August as a preventative measure, even though the old one was OK).
- Remember, this entire gas valve was replaced with a brand new gas valve a couple years back (the previous valve was having the exact same issue), then coils were replaced again 8/19. Something upstream of the coils must be providing rapidly changing voltage/signals. Is there a relay in the system anywhere that could be intermittent?? I'm guessing the coils keep getting burnt out, because new coils immediately fix the problem (temporarily). Anyway, I'll check coil resistance later today, and see what's going on.
 

KenBradley

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Think it's worth replacing the flame switch, or inspecting it? If the igniter isn't glowing, would you expect the flame switch could be at fault? Does Bosch have another name for it? Assume it's the same as the "Flame Sensor #0410"?
 

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rickgburton

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KenBradley

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Hi Rick -

Just took measurements of each sensor/switch in the circuit, here's what I measured:

#0410 Flame Sensor 0.3 ohms

#0411 Igniter 62.6 ohms

#0408 Primary Coil:
terminals 1&2: 2500 ohms
terminals 1 &3: 645 ohms
terminals 2&3: 1600 ohms

Secondary Coil:
terminals 4&5: 1500 ohms

#0325 NTC Sensor (lint screen area): 7300 ohms @ room temp (~20 dec C?)

#0327 Hi-Limit Fusible Protector: 0.5 ohms

#0404 NTC Heater Dryer (at back of flame tube/duct): 28800 ohms @ room temp (~20 deg C)

#0405 Temp Limiter (mid-length along flame tube): 0.1 ohm

#0419 Belt Switch (tested both positions - seems to be working as it should)

Didn't find any open circuits

Does not appear there is any thermal fuse in the dryer, as shown on some other gas models. I also did not see a thermal fuse in the parts breakdown on the BOSCH site.

- - - - - - - - -

Coils seem like they "test" OK in terms of resistance. I ordered another pair, and will replace them anyway.

Flame Sensor has continuity, so "should" be OK.

According to the green sheet (wiring diagram) I sent over to you, appears the NTC sensor (in lint filter area) is reading a bit low (7300 ohms) (should be at 10000 ohms @ 25 dec C), which means it should be an even higher resistance at 20 deg C (10K+). Since it's well over 10% out-of-range, do you think it's worth replacing?

Any other thoughts????

Thanks again!
 

rickgburton

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