have green light flashing above overide worcester boiler?

Hi, Worcester Greenstarr CDi, have green light flashing above override and heating wont come on, have reset and got rid of light but still no heating despite changing batts in remote thermostat. Hot water works ok. previuosly found batts in reverse polarity but corrected and has worked since. Have switched on and off but still no luck

gary Coomber
November 2011