Replacing temp relief valve


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Old 03-08-09, 06:26 AM
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Replacing temp relief valve

My temp relief valve is leaking. Gas water heater. I am going to try and replace it myself. Is it necessary to turn the gas all the way off or can I take it to pilot only. The valve is located at the top of the tank not the side.

Thanks
 
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Old 03-08-09, 06:19 PM
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You are ok going to pilot. But are you sure the TP is bad? A common problem is TP leaking due to pressure too high...failed PRV, or thermal expansion.
 
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Old 03-08-09, 06:37 PM
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Not sure myself. The unit does not have one of those expnsion tanks. Is there an expansion valve that could be bad. How do I determine best course of action.

Thanks for the help
 
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Old 03-08-09, 08:35 PM
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First step is to pull the handle on the T&P valve fully open for a few seconds and then let it snap shut. It will continue to drip for a few seconds while the water is draining from the pipe and it should then stop dripping. If it continues to drip then it needs to be replaced regardless of any other work that may be required.

Second step is to evaluate the expansion tank by pressing the air charge valve stem. If it expels water then you definitely need to replace the expansion tank. If it does not expel water then you need to remove the tank from the system and check the air pressure in the bladder with a good tire gauge. The air pressure needs to be equal to the nominal water pressure of the system. Ideally you will have a means to measure the water pressure using the same gauge but even if you have to use a separate gauge the two pressures should be about the same with the expansion tank being slightly higher preferable to it being lower. If you cannot raise the pressure in the expansion tank (broken bladder) then you need an new expansion tank and you need to set the air pressure in the new expansion tank to be equal to the water pressure.

Third step applies if you have Pressure Regulating Valve (PRV) in your system, usually just after the main shut off valve for the entire house. The nominal water pressure when a PRV is installed is from 50 to 70 psi and is best read with a dial-type pressure gauge. Read the gauge when no water is flowing and also when water IS flowing. It is normal for the pressure to fall a few psi when flowing but anything more than 10 psi is cause to suspect a malfunctioning PRV or plugged strainer before (or built into) the PRV. If the pressure with no water flowing is greater than 70 psi yet it falls to the 50 to 70 psi range when the water IS flowing then the PRV is probably leaking through and needs to be replaced or rebuilt. Since rebuild kits have limited availability and relatively high costs with the possibility of not being able to properly repair the PRV I recommend replacement of defective PRVs.
 
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Old 03-09-09, 06:34 AM
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Thanks for the followup. I will check things out today.

I do not have an expansion tank(9 year old hot water heater)

Again, thank you
 
 

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