What wrong ,the thermostat off but the flame still on?

It is easy to procure the wrong thermostats, sensors, safety switches. They can physically look like just the same old ones, but the voltage limits can be off.

What solenoids are you referring to?

When you set the timer and heat selector switches on your dryer and press the button [switch] to turn it on, the direction of 120VAC passes through the heat selector switch through the timer switch through the cycling thermostat through the hi-limit switch, through the thermal cut-off fuse to the burner assembly's gas valve.

Simultaneously, as the current is traveling through a path to the 1st gas valve coil, current is also traveling through a path to the flame sensor- and then to the igniter.

The igniter will begin to glow and when it gets hot enough, the flame sensor will detect the heat and switch off. which then diverts current to the second gas valve coils.

The second gas valve coils activate plungers in the gas valve which allows gas to flow out into the burner housing. The igniter still being hot, ignites the gas to a long blue flame.

To maintain the proper air temperature, the heat in the blower housing is monitored by the cycling thermostat. During normal operation, air temperature should be between 120 degrees Fahrenheit and 160 degrees Fahrenheit.

When the air reaches the proper temperature specific to your dryer model, the cycling thermostat will switch off the voltage to the burner assembly.

The hi-limit thermostat and thermal cut-off fuse monitor the drum air temperature. If there is an air flow problem [restriction or total blockage], the hi-limit thermostat may switch off the voltage to prevent damage to the dryer.

Eventually, if the air flow problem [restriction or total blockage] is not corrected, the thermal cut-off fuse will fail (blow) and the dryer won't heat at all.

Check continuity to the following components, thermal cut-off fuse, hi-limit thermostat, igniter, flame sensor, and cycling thermostat. Of course you will take your readings with the power cord of the dryer unplugged from the wall outlet.

You will either disconnect [isolate] any of the wire leads going to their respective components during the test [using a multimeter (analog or digital)]; OR remove each of the components entirely from the dryer to test them.

1.) A good thermal cut-off fuse will have 0 Ohms of resistance. On the other hand, if the needle [on a an analog tester] does not move OR the digital display [on a digital meter] has not changed significantly, there is NO continuity - which means the fuse has burned out and needs to be replaced

2.) A dryer's Hi-Limit Thermostat is activated by hi-temperature changes (between 250 degrees Fahrenheit and 300 degrees Fahrenheit.

A good hi-limit thermostat will have 0 Ohms of resistance at room temperature.

To test the thermostat's response to temperature change, place the component on an electric griddle or skillet. Set the heat on the skillet or griddle to the appropriate temperature according to the temperature rating stamped on the hi-limit thermostat you are testing. If the hi-limit thermostat switches off within 5% of that temperature, the part is functioning properly. However, if the hi-limit thermostat does not switch off OR switches off prematurely, the hi-limit thermostat is faulty and will have to be replaced. [Remember, when the switch turns off at the appropriate temperature level- you should get a high resistance reading to show that the circuit is "open")

3.) Perform the same procedure as step 2 to test the Cycling Thermostat: First at room temperature and then its response to temperature change. The only difference is, the test temperature range will be somewhere between 120-160 degrees Fahrenheit Once again, refer to the temperature rating stamped on the component you are testing- and the 5% tolerance remains the same, too.

4.) The resistance reading for the igniter is between 50 and 400 Ohms of resistance; anything else, it's faulty- toss it and replace it.

5.) You should get a resistance reading of 0 Ohms at the flame sensor-

Flame sensors are tricky though. Flame sensors could still short out and allow the igniter to glow- but would prevent voltage from reaching the gas coil. For example, the igniter will glow and not turn off and a flame will not be established because there was no voltage at the gas coil to open up and release gas for ignition.

Hope this info helps...I would appreciate a follow-up from you when you resolve this problem- to gain more knowledge and skill.

Thank-you and best wishes on your project

Hi there.
The thermostat will only shut down burner flame but not pilot flame.
Try tightening all wiring connections.
By using an ohm meter, check the continuity across the hi limit terminals when the pilot goes off, your hi limit may be tripping prematurely causing pilot flame to shut down.
Regards.

Check if your pilot flame sufficiently heats thermopile during operation and make sure also that it is free of soot or any form of dirt, thermopile generates small amount of electricity to energize pilot and main valve of the gas valve for pilot and main burner operation. This electricity passes through hi limit mechanical contacts. Hi limit on fryers act as safety device which will shut down pilot and burner flame when oil temperature reaches 450F.
If your fryer is set at 350F and over shoots up to 450F (which will trip hi limit and shut down pilot and burner flame), the thermostat is not good, but, if hi limit trips on temperature much lower than 450F, hi limit is bad.

I assume it is a gas model. There are 2 thermostats. One is adjustable, you set your temp, it sounds like it has gone bad.. The second thermostat is the high limit thermostat. When it reaches 450 degrees F, it will shut down the pilot and main flame to prevent a grease fire. It may be possible that someone has hooked the thermostat up wrong. Next time you fire it up, disconnect one of the thermostat wires that has the temperature knob. If the flame goes out, the thermostat is bad,

Check the elements first, also check the hi-limit switch and the thermostat, then check the elements the machine might have been low on water at one point.

Replace the 2 coils on the burner valve . That will take care of the problem . Stop wasting money replaceing unnessary parts .

diesel fuel requirs a hotter spark for ignition and burns pretty dirty, better off with K1 kerosene. You could change the ignition system to a mutifuel but it's not cheap and may not mount to your current houseing but would still work. As for restarting it is one of two things: the hight heat limit control or most likely teh CAD flame sensor, both of which you can get from Mr. Heater for less than 3 bucks each. the mount for the limit control is different but you can simply remount it to your heater mount. Same thing with the flme sensor, the wires are different but you can splice the to your wire harness and it will be fine. there is no wrong way to hook them up so don't worry about ground or hot.

replace both the hight limit thermostat and low limit thermostat they come in a kit and also clean dryer vent

it sounds like the dryer is kicking the flame out on a hi limit thermostat. you need to check to make sure that there are no blockages in the vent line. if you can start the dryer with the so you can see the burner. If the flame seems to be very wide and not in almost a straight line that would confirm the problem. there should be a hi limit thermostat on the top of the burner and if the flame is touching or coming to close to the thermostat it will cause your problem