ArrrrrgH! (H.W. TP relief valve)

[Roger Long]

I'm cleaning up the boat preparing for launch when the F.W. pressure set starts cycling every 15-20 seconds. I'd turned on the 110 volt hot water heating coil about an hour before so the hot water tank was the first place I looked for a leak. Sure enough, I could hear a hissing and the hose that diverts the TP output to the bilge was warm.

When I turned off the electric element, the pressure set cycling backed off to only about every 15 minutes. That will still drive me nuts. When this Atlantic Marine hot water heater was plumbed up about 30 years ago, someone put a brass pipe nipple on the water heating loop connection which blocks the TP valve from being unscrewed. Looking at it, I'm pretty sure the heat exchanger connection will simply break long before those threads give up.

The water wasn't especially hot, it's been way hotter in the past when on shore power, but the cycling slows when the electric is turned off so I conclude that the problem is a change in the TP valves temperature setting.

Questions:

Once these valves start to go flakey, is it immediately straight downhill?

Is there a chance that a gasket simply dried out over the winter or some debris from all my recent plumbing is lodged in it somewhere?

Is there a way I can't see to get the guts of the valve out and just replace the working parts without having to unscrew the body?

Should I wait and see or just set aside a couple days to tear it all apart which will likely result in a search for a new water tank?

 

[agaliha]

Bad news

I had this problem last year and found out that the pressure relief valve on a marine water heater is set to a different standard than a household valve. The only one I could find was at Defender, and it was 3/4" npt and mine was 1/2" npt. So I bought a brass adapter and used it. It looks stupid (sticks way off the heater) , but I'm the only one who ever sees it.
I think "once they go, they go." I was mightily tempted to use the household version at the hardware store, but I didn't.
Agaliha

 

[Roger Long]

It looks stupid (sticks way off the heater) , but I'm the only one who ever sees it.

Since I can reach the threads for the hose nipple that directs the outflow to the bilge, I wonder if I could thread on some pipe fittings and just add another TP valve down stream? That would look really, really stupid but a lot better than an $800 figure over in the debit column of Quicken. I just know that other pipe nipple isn't going to come off.

Back when I was considering making my diesel cabin heater hot water system pressurized, I did find a 30 psi TP valve available at a local plumbing supply house.

 

[thereisabelle]

is the nipple long enough to cut out a peice long enough to unscrew the t.p.? a quality pipe extractor could then remove the nipple ends. then two close nipples and a union? to rejoin the plumbing... jb

 

[Scott B]

I'm just going through the same thing myself. PTV, is leaking when hot water tank is on. Tried over the weekend to remove the valve, but was afraid I'd break something... it was stuck good. Do I just put a pipe wrench on on yank real good?

 

[thereisabelle]

these valves are cheap and fail when you dont expect it, say 10:30 sat. nite... one that leaks is a good thing. one that fails to open is well... boom. how is the water pressure on your dock? have backflow preventer? secure a new valve and change it out. use cpvc for your discharge tube. open the cwhtprv now and then to check for air and release it. hope your water heater is easier to get to than mine. jb

 

[Roger Long]

secure a new valve and change it out.

Well, Duh! The title of my OP is due to poor installation and plumbing decisions by the builder in 1980 and corrosion. The tank will have to come out of the boat and the engine exhaust runs in front of it. I wonder if I can get the ends of the heavy hose to come off the muffler nipple after being clamped to it since 1980?

I say again, "ArrrrrrrgH!"

 

[Roger Long]

Update:

I talked to the master plumber at the hardware store and he agreed that just putting a hose nipple on each end of another TP valve and inserting it into the discharge line is a reasonable work around until I feel like taking the hot water tank out of the boat.

 

[Rich Stidger]

Well, let me just observe that a PTV is a Pressure-Temperature-Valve, meaning that it will open to release water if EITHER the pressure exceeds the rating or if the temperature exceeds the rating.

These valves have a temperature-sensing rod coming out of their threaded connection that dips into the tank to sense the temperature of the water. If you place the PTV remotely from the tank (even 2-3 inches) I question if the valve will be able to respond to an over-temperature situation. Pressure should be the same everywhere, so I would expect that if the pressure exceeded the trip point it would release.

IMHO, a remote mount would provide only pressure protection. I don't think I would connect it in this manner.

FWIW, I had a PTV go bad (start to leak) on my tank two years ago (11 year old tank). I could not get a wrench big enough into the space to loosen the valve, so I just replaced the entire tank. Yes, I know it was more expensive, but I rationalized that I was probably nearing end-of-life of the tank anyway.

 

[Roger Long]

I don't think I would connect it in this manner.

Neither would I for normal operation but I use shore power pretty infrequently to heat up the tank. No way the circulating loop from my Newport diesel heater is going to get it too hot. When I'm on shore power, I'll just turn it off as soon as it's hot enough for a shower.

The tank need to come out but but I don't want to tackle that job until next haul out.

 

[Scott B]

FWIW, I had a PTV go bad (start to leak) on my tank two years ago (11 year old tank). I could not get a wrench big enough into the space to loosen the valve, so I just replaced the entire tank. Yes, I know it was more expensive, but I rationalized that I was probably nearing end-of-life of the tank anyway.

So, if I can get a big enough pipe wrench and persuader bar, I should be able to break the pipe dope on the threads? I was afraid I was going to break more than the threads, so was willing to put up with a little leaking.

 

[Bob J.]

As a master plumber & pipefitter, the last thing you want to mess with is the T&P valve on a water heater. If the valve is dripping, trip the handle in an attempt to flush any debris out of it, may work but probably not. The "master plumber" at the hardware store is an idiot & should not be handing out that kind of advice. The 30# relief valve @ the store is for a heating system, not a water heater. A water heater is a pressure vessel & the relief valve is what prevents a water heater from blowing up, meaning it would, it could blow your boat to pieces & that's no BS. Break out a torch & heat the snot out of the valve then pour cold water on it. Do this a couple of times & the valve will spin out without much effort.

 

[thereisabelle]

go bob jennings! not real cozey with the torch though. a good pipe wrench or channel lock pliers, say arrrrgh! and push or pull wichever the case it will go. a street-L and nipple would work as a wrench in a tight place... keep the tank, loose the valve. jb

 

[Roger Long]

As a master plumber & pipefitter, the last thing you want to mess with is the T&P valve on a water heater.

Excellent advice, which, like a lot of excellent advice doesn't fit the specifics. The guy at the hardware store is quite familiar with those and clearly would never recommend doing this in a house.

What's wrong with this picture?

1) The hot water heater is never hard connected to street pressure. There's no provision for even doing so. Maximum pressure is the little Jabsco pressure set, about 25 pounds.

2) Everything is piped with 1/2" plastic hose and clamps, much of it 30 years old. Hard to believe that's going to blow up a S.S. water heater. There would be a hose section between the original and back up valve.

3) The system is seldom heated electrically. On the rare occasions when it is, it is attended.

4) A 30 psi heating system valve provides good margin over the design pressure for the tank and is close to the system pressure.

5) The temperature probe will go in a long pipe nipple before the hose.

What am I missing?

I like to have things right so this will certainly get fixed properly at some point. However, the engine exhaust has to be removed for access. Due to my boatyard's stubborness about the schedule, that means either giving up six weeks of boat usage or having the boat on an exposed mooring or public dock with the engine non-functional. I'll probably also have to replace the entire exhaust line since it is unlikely to come off the fittings after 20 years.

I'm not living aboard (yet) and this heater will get heated up electrically maybe once or twice this season. The exchanger loop from the diesel heater won't send water above boiling temperature to the heater so over temp from that source isn't a concern.

Do you really think it would be better to just short circuit the plumbing and disconnect the hot water heater for the season?

 

[BobM]

Sounds good to me

Update:

I talked to the master plumber at the hardware store and he agreed that just putting a hose nipple on each end of another TP valve and inserting it into the discharge line is a reasonable work around until I feel like taking the hot water tank out of the boat.

I think the chances of overheating or overpressurizing during normal operation are remote. You will blow a hose before you blow the tank. I have operated an fair sized RO system at what I recall being 7-900 PSI and sprung a hose leak without it being a big deal at all. It's not like it drilled a hole in the opposite wall or anything. A pressure washer puts out many times that.

 

[petersea]

When this Atlantic Marine hot water heater was plumbed up about 30 years ago.

Should I wait and see or just set aside a couple days to tear it all apart which will likely result in a search for a new water tank?

Ok Rodger here is my take on your situation....The tank is 30 years old ? I'm surprized there are not other problems with it besides the relief valve. Based on that I would replace it anyway now and not mess with the exsiting value and fittings. Most likely you will spend close to the same amount of time to repair it as replace it You can always try to remove and replace the value and see what happens worst case is you replace entire unit. I would not think you need a couple of days to do this work maybe half a day (not including getting the parts) Replace it and be done with it for another 30 years !

 

[kloudie1]

Owwww , man that is not a fun one, Roger. Only thing I can think of with the back-up valve is that the “test lever” stem may not have enough seal or packing to hold up under the normal pressure if a back up is installed. So it may leak a good bit out of the original valve, stem. Once a valve starts leaking across the seat, the seat gets “cut” by the tiny local jet flow of the leakage across one small spot of the seat. Once the cut starts, the valve is toast unless you can access the seats to re-lap them... not likely, especially in this case. If you are lucky, lifting the lever and blowing the valve a little when cool may clear debris from the seat, but that usually is a very low probability thing. Since water temp and pressure are intimately related, and the hot water tank was probably tested to 150 # or so, I don’t think you have any chance of loss of tank containment with a valve that works reliably at 30 psi. Good luck !

 

[Bob J.]

The chance of the heater "blowing up" is slim as as a few have pointed out, the piping or hoses would in all likelyhood come apart before the heater blew but you need to look at the component. The heater would be more likely to overheat when on the engine than the electric side of the equation but I have to keep reminding myself, it's a sailboat, not a powerboat so you're not circulating thru the heat exchanger continously.

The T&P valve should be replaced with one of an equal rating. On a boat there isn't alot of piping so expansion from the water being heated is usually what causes relief valve problems.

As long as you can get the new T&P sensor in the top 6" of the heater you should be good to go not matter how you decide to configure it. There are alot of reasons to not launch a boat, a busted water heater isn't one of them....

 

[Roger Long]

dOnly thing I can think of with the back-up valve is that the “test lever” stem may not have enough seal or packing to hold up under the normal pressure if a back up is installed.

Good point! That valve stem isn't normally pressurized is it? I can see the geometry of the valve now. I love it when a nugget of real information comes out of these discussions. It will be a hundred bucks of valves and fittings by the time I put in a back up.

As Petersea points out, the tank is 30 years old so destroying it trying to get the fitting off in place doesn't have a huge downside.

I'll probably just bypass the tank for this season. If I'm in port somewhere and really want a hot shower, I'll hook it up again and live with the pressure set cycling until I get out the towel. It only leaks significantly when the 110 element is on so it's probably the temperature spring that has gotten weak.

First, I'll put a pipe wrench on the fittings after some Silkroil soaking. If they break off, I can live without it this summer. Maybe I can get enough slack in the exhaust line by casting off all the hangers.

 

[Maine Sail]

Roger,

Couple of thoughts.

1- The 30 pound relief valve is likely just that, a relief valve, most likely intended for a boiler. Temperature on a boat is considerably important as the PVC hoses are normally rated at 150 degrees max rated temp. Sadly most water heaters come with a 210 degree X 75 PSI T&P valve.

RANT:

I have been working with the ABYC on these mismatch issues and the use of non-regulated hot water heaters heated off of engines. These dangerous situations would NEVER be allowed on residential plumbing and they should not be allowed in marine applications either. EVERYmarine water heater connected to an engine should be mandated to have a tempering valve on the hot water outlet side!!! People and children get scalded on 180 degree + water and this is totally un-safe.

Rant over..

2- With a T&P the temp probe needs to be inserted into the tank.

3- T&P's are one of the most unreliable devices in the P&H industry mainly because once they blow off they rarely seal right again due to crud or a dried out seal. Watts makes big money on these, trust me, I know the Watts rep. If they don't blow they work for a while but over time the seal can still dry and or weaken due to antifreeze etc..

4- Most marine rated 12V water pumps are capable of 25 - 50 PSI depending upon the model. The cut in pressures on many pressure sensitive pumps are about 20-22 PSI and cut outs 35-50 PSI. Even a model with a 25 PSI rating is cutting it close with a 30 PSI relief only valve.


5- While you'll likely never bow off a standard 75 PSI T&P they do commonly go off on boats on temp, especially with engine supplied hot water HX's. I know your engine is raw water cooled so this is a non-issue but with engines running 180-190 and a slight blockage T&P's do get blown off on temp more frequently than they do pressure. It would be difficult to blow off a 25-40 PSI system that is using flexible PVC hose on a 75 PSI T&P which is what most heaters ship with these days. Put 75 PSI into a system running flexible clear PVC and you'll quickly find lots of leaks and if the water is over the 150 temp rating you'll likely also burst the hose. If you were at a dock and connected to street pressure (unwise anyway) you'd want a PRV or you'd blow the 75 PSI T&P on the high street pressures.

6- I think you'd be surprised at how that valve will come off that tank with a pipe wrench. Put one on the nipple coming out of the tank, if there is space, and one to loosen the T&P. Use one wrench to steady the nipple and one to undo the T&P. Of course if this was a steel glass lined tank it may just crumble.

7- You've spent TONS of money to have hot water so I would try to make it right.. If you need pipe wrenches and pipe dope I can drop this stuff off this affternoon...