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

KenBradley

Premium Member
Joined
Nov 20, 2010
Messages
7
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

Appliance Tech - Moderator
Staff member
Joined
Jul 11, 2006
Messages
35,193
Location
Murray, Utah 84107, United States
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
7
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

Appliance Tech - Moderator
Staff member
Joined
Jul 11, 2006
Messages
35,193
Location
Murray, Utah 84107, United States
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.
 
Top