I have a 3 year old H400 (propane) heater that will sometimes cut out then it reignites. I have not had it cleaned. It appears it needs cleaning of the burners/gas jets. I did check wires for contact etc. I do not have a union at gas valve. Can the jets just be removed and cleaned and burners cleaned in place. Do the jets need an special thread sealants. Any advice welcome. I have the manual.