Water heater is overheating

Overheating is most often caused by air in the system or restriction in the coolant flow. 

• First of all, purge the air from the system and check for any restrictions in the coolant flow. 
• Air heat exchangers will have rubber inserts on the coolant ports to prevent damage during shipping. Do not forget to take these out.
• Blockages in the water pump can sometimes cause overheating. If possible, bench test the fuel pump to see if liquid flows freely. If the pump does not work, check for blockages in the pump itself and clear them out.