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Old 03-29-2012, 12:56 AM   #1
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T&P valve on Tankless Heater


I have a Tankless heater, for a while now 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?

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Old 03-29-2012, 05:33 AM   #2
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T&P valve on Tankless Heater


The TP valve should not normally leak. I would change it. If the new one leaks, the pressure in your system is to high and you could need an expansion tank.

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Old 03-29-2012, 08:40 AM   #3
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T&P valve on Tankless Heater


nothing has changed in the system so why the need for an expansion tank now?
This is not a closed system, just a normal household system.
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Old 03-29-2012, 10:20 AM   #4
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T&P valve on Tankless Heater


You shouldn't need an expansion tank on a tankless water heater.



I'd check the pressure on the house before you go to the extent of changing the T&P valve.

I'm betting the pressure is a little high, and the act of water hammer is pushing the valve open a little.
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Old 03-29-2012, 10:54 PM   #5
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T&P valve on Tankless Heater


If the pressure is high to the house then why would lowering the tempo make it leak less?
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Old 03-30-2012, 11:50 AM   #6
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T&P valve on Tankless Heater


BTW, manufactures typical specify a pressure, not a temperature and pressure, relief valves on thankless WHs.
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Old 03-31-2012, 11:14 PM   #7
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T&P valve on Tankless Heater


Change it with one with the same rating, works good now

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