Ring TRANSCO on 0800 111 999. If the problem is external they will fix it. If it is diagnosed as an internal fault call CH4 Heating Solutions Ltd on 0161 748 9226 for further advice.
From time to time, your central heating system may require bleeding at various points around the home.
If you rent out a property then as a landlord you are responsible for ensuring that all gas fittings and flues are maintained in good order and that gas appliances and flues are checked for safety every 12 months.