After defrosting coils and getting fridge running again I checked the lower radiant heater and it appeared to be burnt out. I checked my timer by advancing the cycle manually after being advised by appliance pro where it was located and it appeared to be functioning properly. Ordered new radiant heater from appliance pro, replaced the old one and now all seems to be working properly. I also replaced the defrost thermostat at the same time. Note it is tricky getting all the wiring for the old heater out and new one in but not impossible for diy.