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Old 10-05-2011, 07:04 AM   #1
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Join Date: Oct 2009
Location: South Eastern PA
Posts: 23,269
Water Heater Pressure Relief Leaks


The majority of RV water heaters and motorhome water heaters are either Suburban water heaters or Atwood water heaters. RVs, which do not have Suburban or Atwood water heaters, are usually high end motor homes which may have either instantaneous water heaters or some type of engine assist water heaters. Here we’re going discuss leaking, weeping water heaters, or more specifically weeping pressure temperature relief valves. (Commonly referred to as P&T relief value)
P&T relief valves can be an area of confusion for RV’ers until they understand the purpose and function of the P&T valve and whether or not they are functioning properly. In other words a P&T valve which is always weeping way not necessarily be bad. Let me explain why.


RV water systems are closed systems, which mean there must be a means of relieving excess pressure when it develops. The obvious question then is what would cause excess pressure to develop in the tank. We know H2O expands when heated so we might then conclude there is always excess pressure in the water tank. This is true…only to a point however. A properly functioning RV water heater always has an air expansion pocket in the top of the tank. What is an air expansion pocket? It is simply an air pocket, which naturally forms in the water heater tank when it is filled.

As long as this air expansion pocket is of sufficient size, the only time the P&T relief water valve will weep is during the heating cycle. However, as hot water is taken from the tank the size of the air expansion pocket will diminish eventually to the point where the tank is practically full of water. When it reaches this point the inside pressure of the tank will almost always be excessive ( over the 125/150 psi rating for the P&T valve) resulting in excessive weeping of the P&T valve.

RV’ers not aware of this may mistakenly conclude the P&T valve is bad when it is not. (Emphasis added. FM) To further complicate matters they may replace the valve and in the process re-introduce an adequate air expansion pocket and then it will naturally work fine…until the air expansion pocket is diminished again and the whole process repeats itself. RV’ers replacing numerous P&T valves are most likely doing it needlessly. So what is the answer?

Reintroduce an adequate air expansion pocket and this is how it is done:

1. Turn water heater off.
2. Turn off water supply (city H2O or H2O pump)
3. Open closest hot H2O faucet in RV.
4. Open the P&T valve by pulling on handle at end of valve and allow H2O to flow until it stops.
5. Release handle on P&T valve – it should snap shut. ( do this a couple of times as it may stick)
6. Close hot water faucet.
7. Turn on H2O supply – Now that everything is closed the tank will refill and air expansion pocket will be re-established.
Repeat the above procedure if P&T valve continues to weep between heating cycles. If this is not successful then the P&T valve should be replaced.

Special Thanks to Frank Martinez - Miami
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