T&P valve on Tankless Heater

I have a Tankless heater, ever since I bought the house 1.5 years ago the T&P valve has been discharging slightly when you turn off a hot water tap. I was told this is normal. Is it?

Now the T&P valve is leaking constant when you use hot water. The water temperature is not overly hot coming out of the relief vlave, I can hold my hand in a pail of it for a minute or so. Wanted to take a temperature on it but do not have a thermometer.

The tank was at 50C and I turned it down to 40C and it leaks a lot less water but still does leak a little.

We also had a power outage if that makes any difference, although we were on holidays, however 4 showers were taken and 3 loads of laundry done before it started to leak after we got back.

Figuring I'll probably just change the T&P relief valve and see if that does it.
Any other thoughts or ideas?

I would change the T&P
Sometimes they get something inside that prevents sealing.

do you know the temp & press setting of the valve? is there any check valves in the system? it seems like it's narrowed down to a pressure issue. not overheating.

Old pressure relief was 201f and 150psi(?) just going from memory, replaced it with the same and seems to be fine now.

Thanks