Lot of hoo-wee going on about T&P Relief Valves on RV water heaters..........which are the SAME T&P Relief Valves used on residential water heaters. Only difference is smaller tank size.
Rv Water heaters Atwood/Suburban by design have an 'air pocket' at top of water heater tank.
Air can be compressed--water can NOT be compressed.
Water swells when heated....air pocket allows for the swelling of heated water.
W/O Air Pocket the swelling hot water causes the T&P Relief Valve to 'weep'
Continuous weeping causes mineral/scale build up on seat of T&P Valve which causes more weeping.
Re-establishing the air pocket CAN stop weeping IF valve doesn't have scale built up
Rotating the lever causes valve stem to rotate which can help valve seal against valve seat.
A good blow out under pressure thru T&P can help remove build up.....then let valve SNAP close by letting go of lever (do this when water is cold)
T&P Relief valves OPEN when TEMP/210*F and/or PRESS/125# starts to open--full open at 150#
Turn off water supply
Open nearest faucet hot side to relieve pressure
Open T&P via Lever...let snap close when water stops running out
Open water supply
IF air pocket/exercising T&P etc does NOT stop weeping/water running from T&P
REPLACE IT.........1/2" NPT and 3/4" NPT thread size have been used