re citroen zx 1.4 petrol injection 1994..

i a m having problems with the sensor for the stepper motor which is that the sensor has no hot water flowing over it due to a possible blockage in the cylinder head, is there anything i can use by adding to the water to unblock this blockage.. i found out this when i took out the old sensor and no water came out of the block.. any help will be helpfull... thanks rp210526