When walking on treadmill and it slows down are it's stops.

Hi, It's probably the speed censor. Clean it up and should be good to go. When you disasemble it clean all other parts and put back togeather. Good luck

treadmill stops all of sudden when i am walking

Make sure that the walk belt is tight ( about 2 inches of deflection at the edge). Do you smell anything or hear anything before it quits?

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The walking deck needs lubricated if it continues after lubricating replace the controller

It sounds like the belt is bogging down, this condition is when the treadmill operates normally without a person on the belt and then slows down when someone steps on the belt or when the treadmill operates normally for a given period of time with someone on the belt then abruptly begins to slow down.
The only certain way to test for a worn walking belt is to take a DC amp draw . Trying to look at the belt or a feel test is highly unreliable. Better tests, if you lack a DC ammeter (they are expensive for a good one), are a coast test or an incline test.
The coast test is to get on the treadmill as the lowest incline setting and walk on the treadmill at 3 MPH. Pull the safety key and it should take you 2-3 full steps to stop fewer steps indicate high friction.
The incline test is to put the treadmill at max incline and walk on it at 3 MPH. If the treadmill operates normally at max incline but bogs down at minimum incline, replace the walking belt. Gravity takes over for the drive system eliminating much of the friction problem. On some heavily worn walking belts, this test will not eliminate the problem.

The walking belt slows when walked on the walking belt maybe overtightened, treadmill performance may decrease and the walking belt may become damaged or the opposite the drive and /or running belt may need tightening. Last thing would be that the belt needs lubrication to be applied between belt and deck.

I believe under the motor shroud on the circuit board their should be 2 pots 1 adjusts torque 2. adjusts speed try adjusting them and see if that take care of the problem if not. worse case it might be the drive motor.

You need to replace the walking belt.

Sounds like it is overheating, you have to disassemble the unit and find why it might be overheating

Check both belts to be sure they are adjusted and not slipping.Check the underside of the walk belt to see if it feels frayed in the center as compared to the edges, the center always wears more than the edges a really worn belt must be replaced. if it is nor worn there is a wax lubricant for proform treadmills that can be purchased at retail stores that sell treadmills.Sears, dicks sporting goods and also treadmilldoctor.com are good places to buy it.