Plumbing pressure relief

Old-Biscuit wrote:
T&P on RV water heater will weep at 125 psi


Not many RV MFGs install a check valve on INLET
And not many have issues with T&P weeping but it does occur
Some can experience weeping EVEN with an air pocket....that is where an accumulator tank can help
** most install accumulator tanks to help with pump cycling during low demand & being able to turn pump off at night and still be able to flush the toilet
But they will also help control system pressures

My WH Tank does NOT have ANY check valves..has 3 shutoff valves
And even w/o check valves I have never had T&P weep except when air pocket was lost.

I think the thread has drifted a long ways from the OP..

To refresh, I am quoting the OP that started this thread...

I am Yu wrote:
I'm running on internal water (not city water). I don't leave the water heater turned on all the time (too wasteful to do so) and when I turn it on it raises the pressure in the whole plumbing system way too high, and I get water leaking from the toilet onto the bathroom floor. The only way I've found to deal with this is to shut off the pump and briefly open a faucet every 10 minutes to relieve the pressure, until the heater gets hot and the pressure stabilizes, which gets pretty annoying.

There is a pressure relief valve on the water heater, but apparently it's only intended to protect the heater tank, and opens at too high a pressure to do anything for the plastic plumbing.

Is there some kind of relief valve that opens at a lower pressure, which I could install somewhere in the system and have it drain overboard?

So, the real issue the OP has is the TOILET LEAKS, but ONLY WHEN THE WATER HEATER IS RUNNING.

To "fix" OP turns off the water, bleeds down the pressure on the water heater then restarts everything.

So, the REAL issue is the TOILET leaks when there is MORE PRESSURE.

Bleeding pressure off the system stops the leakage.

Issue IS NOT the water heater, nor is it lost air space nor is it not having a bladder tank..

The issue is most likely the TOILET FILL VALVE IS FAULTY and it shows up ONLY when there is more pressure.. I HAVE BEEN THERE DONE THAT.. Relieving pressure is just hiding the symptom temporarily.

Op needs to gain access to the back of toilet where that water line connects to the fill valve and observe EXACTLY where the water is coming from.