By Chris Noble
If you have a water heater in your RV then you have a device called a pressure and temperature relief valve (P&T for short). The P&T is located on the outside of the water heater and it provides a most important service: to keep you safe. Don’t believe me? Watch a YouTube video on exploding water heaters and you will be convinced.
With that being said, the P&T valve can also annoy the heck out of you if it drips every time you fire up the water heater. I’ve heard that it’s “normal” for a P&T valve to drip on Atwood water heaters, but I can tell you that water dripping anywhere is not normal. If it is only dripping, then it is relatively safe — but certainly not normal.
So, what can you do about it? One of three things: You could ignore it and let it drip (not the best thing to do). You could replace the P&T valve (not overly difficult or too expensive). Or you could try to repair it and save a few dollars and be rewarded with not throwing away a perfectly usable valve.
In your water heater there is usually a small pocket of air in the top of the tank which compresses as the water heats up and expands. This is perfectly normal and desirable. The Atwood service manuals address the dripping P&T valve by stating that sometimes that air bubble gets filled with water, so there is no room for the water to expand and the P&T valve does its job and lets a little water out to relieve the pressure. The service manual goes on to say that it is not a defective valve— you can turn off the water heater, allow the water to cool, then open the P&T valve (with the water off). That will sometimes resolve the dripping valve by putting that air pocket back into the top of the tank. No need for a replacement of the P&T valve.
Fair enough, but sometimes it works — and sometimes it doesn’t. Oftentimes it doesn’t work because there is either a small bit of sediment or, depending on where you get your water, lime or calcium buildup that clogs the valve when it opens to let out that excess pressure. So what if putting the “air back in” doesn’t work and your valve continues to drip? Replace it? Not so fast. Here is a handy tip to try first.
First, make sure that your water tank and its contents are cool! You don’t want to get scalded. Next, turn off the water supply and remove the drain plug (might as well flush the tank while you’re at it). Now, remove the P&T valve from the tank — it simply unscrews just like the drain plug. If the innards are not overly corroded or damaged in any way, take the dripping valve and pull the small lever out so that the valve is fully open and place it into a container (I use a gallon-size zip-lock bag) with enough white vinegar to completely cover it and leave it to soak for about 24 hours. Occasionally (mostly because I am a curious type), I remove it from the vinegar and actuate the lever just to make sure that the sediment is breaking up.
The next day you just may be amazed at how much gunk comes out of that thing. Now, clean the threads on the water heater, wrap some Teflon tape on the threads of the P&T valve and reinstall it. Put your drain plug back in, fill the tank with water and fire it up. If it still drips, then replace it. But chances are you are back to dry and saved yourself some bucks and didn’t throw away a perfectly good valve.
Oh, and just an FYI: If you do replace the valve it is a Cash Acme NCLX with 1/2″ threads, so shop around as they can be had for about $15. Hope this helps.
Editor: Several water heater pressure relief valves are available at Amazon.
photo: Chris Noble