I have a gas heater rinnai econ 850 connected to gas by a bayonet. It is about three years old and has been fantastic. I have just tried to use it for the first time and the after about 10 minutes the flame goes out and stops. I have just tried again and now it will not stay on at all.

Any suggestions please

I am not familiar with that type of gas heater. Please describe it. Is it a central heater?