Heating Help

Oil fired water heater

I replaced the t&p valve on the water heater 1 month ago. It's now dripping again, after we turned the water temperature down, what could be the cause?

P.S. We did purchase the properly rated t&p valve

While you are waiting for a pro to answer, ...

... you might check the following things,

1,) What is the temperature you get from the water on the way out of the heater? I.e., is it too hot (thermostat not working?)?

2.) What is the pressure of the domestic hot water?

These two items might let you know if the valve is bad, or something else. While it is unlikely that the new valve is defective, it is possible.

3.) When was the hot water tank last drained? It could have crud in it that prevents the valve from seating properly,

4.) is there a check valve on the way into the building, possibly followed by a pressure reducing valve? If so, is the pressure reducing valve adjusted correctly and working correctly? If there is a check valve, it should be a backflow preventing one. The pressure reducing valve may have quit. If there is a check valve, perhaps there should be an expansion tank on the way into the hot water heater. If it was omitted, or if it has failed, you could get the p-t valve to open once in a while.

Dripping relief

Sounds like you may need a thermal expansion tank. If you have high incoming pressure, a check on the water line, as JDB said, with thermal expansion, you will be prone to a dripping relief. On a residential water heater, an Amtrol ST-5 tank will likely solve your problem

Dripping Oil Fired WH:

Oil fired water heaters are notorious for "Stacking" water from short draws and causing the relief valve to drip. I've only ever seen one oil fired water heater drip from expansion. All the rest dripped from stacking and were dripping from high temperature water. Once they drip a little, the washer is ruined and they drip like heck until changed.