Linux – libmodbus trouble with reading from slave

I have the following code for connection to a temperature sensor as my slave using the libmodbus library in C,

#include <stdio.h>
#include <stdlib.h>
#include <modbus.h>
#include <errno.h>
int main()
{
  struct timeval old_response_timeout;
  struct timeval response_timeout;
  modbus_t *ctx = NULL;
  int rc = 0;
  uint16_t tab_reg[64];
  int i = 0;
  int slave = 0;
  int connected = 0;
  int serial = 0;
  ctx = modbus_new_rtu("/dev/ttyS1", 9600, 'E', 8, 1);
  if (ctx == NULL) {
    fprintf(stderr, "Unable to create the libmodbus context\n");
    return -1;
  }
  modbus_set_debug(ctx, 1);
  modbus_get_response_timeout(ctx, &old_response_timeout);
  response_timeout.tv_sec = 10;
  response_timeout.tv_usec = 0;
  modbus_set_response_timeout(ctx, &response_timeout);
  modbus_set_byte_timeout(ctx, &response_timeout);

  slave = modbus_set_slave(ctx,247);

  if(slave == -1)
    printf("Didn't connect to slave/n");

  connected = modbus_connect(ctx);

  if(connected == -1)
    printf("Connection failed\n");
  if(connected == 0)
    printf("connected\n");
  //serial = modbus_rtu_set_serial_mode(ctx, MODBUS_RTU_RS485);
  //if(serial == -1)
  //  printf("Didn't set serial mode/n:%s\n",modbus_strerror(errno));
  rc = modbus_read_registers(ctx,0x27,2,tab_reg);

  if (rc == -1) {
  fprintf(stderr, "%s\n", modbus_strerror(errno));
  return -1;
  }

  for(i=0;i<rc;i++)
    printf("degrees %d\n", tab_reg[i]);

  return 0;
}

It fails in the following section of code,

  rc = modbus_read_registers(ctx,0x27,2,tab_reg);

  if (rc == -1) {
  fprintf(stderr, "%s\n", modbus_strerror(errno));
  return -1;
  }

with a connection timeout. could this be due to me setting up the connection to the modbus device the wrong way, or are there any libmodbus library problems anyone knows of that could be causing this? I am using this device http://www.epluse.com/en/products/humidity-instruments/humidity-measuring-modules/ee071/ on Redhat Linux 6.5.