I presume it is gas powered? They are available in all sorts of dual fuel variations. When you operate one element all the igniters spark. It sound like the igniter switch for the oven need adjusting. They normally operate on a cam so when you turn the control knob, the cam lobe runs up onto the micro-switch and then off it again creating a ignition spark on the way.
It is a gas appliance, so call for service.
Various other suggestions here
https://www.google.com/search?q=Rangemaster+Professional%2B+oven+igniter+keeps+clicking
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If the LPG cylinders have the correct pressure regulator, no need to use an extra one but any regulator must be set to the correct pressure or removed.
Bolcked injectors and blocked burner jets . I would also check and see if you have a valve on the that might be not be fully on . All points to lack of gas pressure I would also check the reg on your tank or bottle .
The thernocoiple works off the saftey device .so if its shutting off the coming back on then the fault is with the saftey valve letting gas pass in the off postion . Check with range master to see if there is a recall on this model . or ask for a replacment stove .
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It's a safety feature that it goes out but this situation is dangerous. Do a normal cooker cleaning and see if that helps. Otherwise you must call a gas engineer.