Compensating cable Problem

Ours is a Glass fibre plant and we have 32 nos of bushings ( From where molten glass is drawn in the form of fibres and wound on bobbins)The bushing temperature is sensed using 'R' type T/C's.The T/c length is 0.5 metre.This is then connected to a PID controller UT321( Yokogawa make )via 'R' type compensating cable situated at a distance of 25 metres in a control room with a contol ambient temperatute of 26 deg +/- 4 deg cent.The controller setpoint is 1100 deg cent.Now the problem is that whenever the bushing stops i.e when the fibres are not drawn the temperatute surrounding the T/C & compensating cable increases to around 70 to 80 deg since the bushing temperature increases and it goes on incrreasing leading to a thermal runnaway situation.The pid controller however shows a steady temperature of 1100 deg cent ( which is the controller setpoint ).It is also noted that the PID controller o/p goes on increasing and the bushing becomes very hot.The operator then has to put the controller in manual and decrease the temperature of the bushing to bring the temperature to normal.Our accesement is that the compensating cable is not able to compensate for the increase in temperature surrounding the junction and ends up giving wrong mv ( less then actual ) to the controller which in turn takes action to maintain the temperature by increasing the output leading to thermal runnaway of the bushing.We have tried thermally insulating the junction and it works which proves that our accessment is right but we feel that the issue is of compensating cable temperature limits.Is there any restriction on the max junction temperature up to which the compensating cable can work.Pls give ur valuable comments and help us solve our problem.