No, you don't need anyone from rangemaster.
No, an electrician is no use either.
You really need a whitegoods engineer to sort it out.
Although the warmer is the most likely cause it could be the wiring, the regulator controlling the warmer, the warmer or a combination of the above.
You can choose to either have an engineer come in on a call out/hourly rate plus parts or have it repaired on a fixed price that includes parts and labour.
For the fixed price repair, go to www.repaircare.co.uk and fill in your details.
They will give you a price and you can book your own appointment if the price is acceptable.
For an engineer that covers your machine and area, click here
Fill in the details, follow the links and it will show engineers in your area.
Select one and they will contact you to arrange an appointment.
Hope this helps
Let me know how it goes