Atwood GC6AA-10E
Combo Gas/Electric that uses Common 12VDC for controls,
Common Set of T-stat/ECO, common Thermal Fuse and a circuit board
Circuit Board has separate circuits for gas & electric
Both Gas & Electric should heat to 140*F (same t-stat)
IF temp gets too hot on either heat source the ECO (Energy Cut Off) trips at 180*F. Locks out the Water Heater and triggers RED Fault light
T&P Relief Valve can 'weep' when heating occurs ....water swells when heated/pressure increases
AN Air Pocket in top of tank helps control the pressure increase
If issue was T-stat.......would affect both gas & Electric
If circuit board electric circuit was an issue......should OVERHEAT/ECO trip/T&P Blow
*DC Relay triggers AC to element (Yellow wire sends DC to that Relay and if Relay fails AC can go to element w/o any controls)
ON EDIT:
REREAD the Post
You stated :
we try to use the electric heat it doesnt shut off at temp and blows the PRV.
The DC Relay is stuck closed.....AC to element will be continuous'
T&P Blowing is the only safety device preventing water heater from over pressurizing
DO NOT USE ELECTRIC until you REPLACE the DC Relay
Located on backside of WH Tank under the protective cover ...same place element is