Water heater T&P valve problems

[Wanderwind]

We've never had the water heater working correctly for the nearly 3 years we've owned our Passage 42. It has the standard Seaward S600 and PB tubing. I have solved several issues including a bad thermostat causing the safety thermostat to trip and the T&P valve spraying water everywhere. The T&P valve would always leak, though, so we almost never used the water heater.

I'm trying to solve this problem. So, I replaced the T&P valve but it continues to leak approximately 10oz of water per cold-to-hot cycle.

Initially I thought the replacement valve may also be bad, but I noticed that when I open the hot valve at the galley sink, a blast of higher pressure water comes out first. So, maybe the expansion of the water in the water heater is actually causing the water pressure to increase and trip the T&P valve.

The T&P valve is rated at 150psi and that seems like an awfully high pressure to be subjecting the 25 yr old PB plumbing on the boat to.

I am hooked up to city water at the dock with one of those cheap RV "40-50psi" regulators.

There is a small accumulator tank on the cold side, right after the water pump and before the T to the water heater. It was originally at 30psi because we were using it as an accumulator. I pumped it up to about 45psi in an attempt to use it as an expansion tank for the water heater but it made no appreciable difference.

Now the confusing part: I have tested it several times and the cold side won't have the higher pressure burst of water, only the hot side. I can't find a check valve anywhere but it doesn't make sense that the of water would only go out one of the pipes on the water heater.

Shouldn't I be seeing the higher pressure on both the hot and cold sides?

Is there a check valve inside these water heaters?

I don't see anything on the parts diagrams of the water heater or looking at the pipes themselves.

Any ideas?

Thanks,
Daniel

 

[jviss]

I can't find a check valve anywhere

I guess you have a check valve that you haven't found yet.

Also, the T&P valve should have a tube leading the overflow t0 a safe place, no?

 

[Ron20324]

In my condo I get that blast of hot water in the morning, when the pipes sat all night chilling, then the neighbors turn on the hot, the pipes and water heat up, and I get sputter of hot, then it comes on okay. Do you have the manual for the heater to tell you how to vent the heater as/after to fill it? There probably is no check valve.

 

[Jim26m]

Unless you have some gauge readings at various points, starting with the city water pressure; and after your regulator, we'd all be guessing. @Ron20324, if I understand, is suggesting you have air in the hot water system. Could what you describe as a "high pressure blast of hot water" actually be air in the system? Without gauge readings to prove otherwise, that would be my guess also.

What temperature water are you making? The T&P may start bleeding water around 210 F. So, if you're running too hot, it will bleed even if the valve is good.

Bottom line, you need some temperatures and pressures to run this down. And... I have had a new T&P be bad right out of the box.

 

[Wanderwind]

I guess you have a check valve that you haven't found yet.

Well, that's what I was thinking too. There just isn't much to it... It would have to be integrated into another component where I wouldn't expect it. The water pump, accumulator, water heater and T off the cold side are probably all within a single compartment. (See attached)

The city connection is T-d off the cold side of the transom shower. Which means there can't be a check valve anywhere on the other side of the cold-T for the WH because water can travel both ways into the WH (from the boat side of the T and the pump/accumulator side).

Also, the T&P valve should have a tube leading the overflow t0 a safe place, no?

Not currently. It had nothing attached to it when we got the boat. When I replaced the valve last week, I added a hose barb and a couple feet of hose, intending to drill a hole in the sole and route it to the bilge. However, the midship freshwater tank is directly under that area of sole and fairly large (85 gal).

So, I need to verify clearance above the tank before drilling or route it a different way, possibly following the path of the tank feed line (up and to the left in the photo)... need to buy more hose if I do that...

Either way, I don't like the idea of using the T&P valve to deal with the extra volume created by heating the water. I'm considering replacing the little 24oz accumulator with a 2-gallon expansion tank like used with residential water heaters. But if the pressure is only coming out of the hot side, a bigger tank isn't going to change anything.

 

[ice breaker]

Unless you have some gauge readings at various points, starting with the city water pressure; and after your regulator, we'd all be guessing. @Ron20324, if I understand, is suggesting you have air in the hot water system. Could what you describe as a "high pressure blast of hot water" actually be air in the system? Without gauge readings to prove otherwise, that would be my guess also.

What temperature water are you making? The T&P may start bleeding water around 210 F. So, if you're running too hot, it will bleed even if the valve is good.

Bottom line, you need some temperatures and pressures to run this down. And... I have had a new T&P be bad right out of the box.

I agree with Jim. I would guess that the "new" temp regulator is still not working and the water is getting too hot before it shuts off. If the water gets too hot it will vent out Temp and Pressure safety valve. It is not just based on pressure.

 

[Wanderwind]

Could what you describe as a "high pressure blast of hot water" actually be air in the system?

It's definitely a blast of much higher pressure water and not air coming out.

What temperature water are you making? The T&P may start bleeding water around 210 F. So, if you're running too hot, it will bleed even if the valve is good.

The thermostat is factory set and fixed at 140 F. I replaced it a couple of years ago because it was faulty and the water heater would run until it tripped the safety high-limit switch. The high limit switch trips at 190 F. It stopped tripping after I replaced the main thermostat.

Bottom line, you need some temperatures and pressures to run this down. And... I have had a new T&P be bad right out of the box.

If it wasn't for the blast of water, I would assume the valve was defective also. I'm still confused about why I'd get high pressure on the hot side and not the cold. Even if I run the cold side first, the hot side will still have the blast after heating the water. Makes no sense.

I can measure the temperature, but subjectively, I can put my hand in it. It feels very hot but it's not instant-scald territory. My completely non-scientific estimate is that it is right around 140. Based on this, the high-limit switch not tripping anymore, and my observation of the pressure blast on the hot side, I do not believe the T&P to be leaking due to high temperature.

I guess I'm going to see if I can find a pressure gauge locally and plumb it into the system at various points and run the water heater to collect more data.

 

[Wanderwind]

I agree with Jim. I would guess that the "new" temp regulator is still not working and the water is getting too hot before it shuts off. If the water gets too hot it will vent out Temp and Pressure safety valve. It is not just based on pressure.

Ok, I guess I'll get a thermometer and measure the temperature also.

 

[Jim26m]

The pump is the only obvious check valve in the system. It doesn't appear to be in a position to create the situation you're seeing.

And you are exactly right. If the water was 210F, you would know it instantly. Even 140F is difficult to keep in contact with.

I assume you verified the pump isn't running while you're on city water?

So far, you have a real puzzler. May help to try to draw and post a schematic if you don't run it down. I see the parts in the photo, but don't get a good picture of what else is in the system, i.e. Tank changeover valves, isolation valves, etc.

Regulator may be acting as a check, but doesn't explain the hot/cold differential. Home Depot / lowes sells a hose end pressure gauge cheap. I might check the hot vs cold system pressures first to verify that there is a pressure differential at no flow. If the heater is partially air bound, it can act very strange.

I can create a scenario, that involves an air bound heater and flashing steam, that might explain what you're seeing, but until we've had a better look around for the obvious, we'll hold off on the bizarre.

Good Luck!

 

[Terry Cox]

Our 1991 P42 came with a six gallon Seaward hot water tank, but no expansion tank. Never had a problem with it since purchasing the boat in 2002, and we use it a lot during our extended cruises. Maybe five years ago replaced it with same and again no problems. Basically plug and play with no leaks, no discharge, no flashing steam, etc. Unsure why yours is causing such a problem. Please let us know what your sharp eye turns up.

 

[jviss]

So, maybe the expansion of the water in the water heater is actually causing the water pressure to increase and trip the T&P valve.

I think that's what's happening. It also requires a check valve between the cold supply and the heater to behave this way, essentially isolating the hot water circuit from the expansion tank in the direction of hot to cold (and not the other way).

For context:

I have a Tartan 3800 with PB tubing, an expansion tank, and a 10 gallon water heater. I'm not using dock water pressure. I put a pressure gauge in the leg just beyond the pump, as I was debugging things. (I still have some weird issues.) I have no check valve before the water heater yet, 'though I've purchased one. Now I am having second thoughts.

The expansion tank is a 4 gallon unit just past the pump. It currently serves all downstream needs, hot and cold.

After reading of your issue, I think you would need an expansion tank on the hot side if the hot side is isolated by a check valve.

Find and disable your check valve, or install an expansion tank on the hot side, is my recommendation.

 

[jviss]

BTW, the reason you should fix this soon.

"“It was pretty quiet, then all of a sudden there was this huge explosion,” A report from a Baghdad street or perhaps the statement from a witness to a gas explosion? No, in fact this is a quote from a story about a water heater that exploded in a Seattle suburb in 2001. The water heater began life located in a restaurant and its career ended more than 400 feet away in the parking lot of a Pizza Hut. Its meteoric traverse took the appliance over several businesses and a busy four lane intersection. Four bystanders were injured and several buildings were severely damaged as a result of the concussion. Although not common, water heaters have been known to explode in this manner from time to time. Reports in the case of the flying water heater indicated that the pressure relief valve had been capped and the water heater partially drained,the combination of which created a steam explosion. The thought of this occurring aboard a cruising vessel is, well, unthinkable."

Read the whole thing: https://stevedmarineconsulting.com/water-heater-primer/

 

[Ron20324]

Per the Atwood EHM xxxx model manual, A dripping relief valve does not mean it is defective. Releif valve should be set to 100-125 psi. Parts diagram list a 150 and a 75 available. The Atwood (maybe ALL tanks?) are designed to have an air gap at the top of the tank. This means water should not be as high as the relief valve and it should not drip. In time, this air will disolve and needs to be reset. to reset the air gap:::
1. turn off the boat water pump or water source.
2. Let water cool, or run until it is cool.
3. open hot water faucet closest to the heater.
4. Pull out handle of relief valve until water stops flowing.
5. allow the valve to SNAP SHUT.
6. Turn on water to fill, turn on water heater and test.

 

[Jim26m]

Couple of different possibilities for the 10oz seepage per warmup cycle.
There will be a volume change when you heat the water from cold to hot (as many others have noted). We'd have to have specifics to calculate it, but it will likely be around a quart for a six gallon heater from 60 F to 120 F. Your idea to use your pressure tank to absorb the expansion was spot on. You increased the air pressure to 45psi. You fill the the system with a regulator that's 40-50psi. You have a roughly balanced pressure between the accumulator and fill pressure, so at 24oz volume of the accumulator, and actual pressure from the regulator, it may become waterlogged during the warmup cycle.

At any rate, the 10 oz leakage per warmup cycle may be purely due to volume change due to thermal expansion. If it were piped to the bilge (or overboard), you'd probably never have noticed it. Expansion tank of adequate volume would likely stop it.

Also, from the S600 manual:
NOTICE
This temperature / pressure valve may weep during initial operation. This is normal. The valve will seat itself with use. A drain hose should be installed at this valve directed into bilge. If the boat is connected to the dockside water system, make sure to turn off the system at the dock when not attended. Also make sure a pressure regulator is used to control pressure.

Need more beer to get my head around the different hot and cold supply pressure issue... West marine (and others) show a check valve in the cold supply to the heater in their hookup schematics. Your photo doesn't appear to show one there.

 

[Wanderwind]

Our 1991 P42 came with a six gallon Seaward hot water tank, but no expansion tank. Never had a problem with it since purchasing the boat in 2002, and we use it a lot during our extended cruises. Maybe five years ago replaced it with same and again no problems. Basically plug and play with no leaks, no discharge, no flashing steam, etc. Unsure why yours is causing such a problem. Please let us know what your sharp eye turns up.

Terry, thank you for sharing that. Makes me think I may just cut my losses and replace the whole thing. I have no idea how old it is, but judging by the patina of the exterior, probably at least 10 yrs.

Since you have the same make/model boat... Where does your T&P valve hose go? Or is yours missing like ours was when we took possession?

Sooo... I got a pressure gauge at the store. Didn't realize till I got back to boat that the scale is kind of weird. Hoping someone can explain how to read the scale on this thing:
https://www.orbitonline.com/products/sprinkler-systems/tools/tools/pressure-gauge/pressure-gauge-367

Why are there 4 ticks between 20 and 40? 24, 28, 32, 36 psi? Am I missing something?!

Replacing the whole water heater is sounding like a great idea right about now...

 

[Ron20324]

Maybe the external expansion tank is overpowering/over riding the air gap in the water heater. I've never heard of one used like you have, but maybe people do it ??? No one else has chimed in they have one that way. Yes, maybe it can work, but on the other hand, SOMETHING is not working.

 

[jssailem]

I am going to guess that the Orbits pressure gauge does not have a lot of precision. It should be good enough to give you general information about the pressures in your system.

I know that even 30 psi will spit when coming through a narrow opening like the sink faucet. You said you were connected up to city water. That would be 60 psi. That is unless you have a functioning pressure regulator that is reducing the 60 psi city pressure.

I replaced an old Seward unit on my boat. I figured it had served more than 10 years and even if it could go another 2 then fail I would have to deal with a failure that might not be in the marina and near resources. Sometimes it is better to bite the bullet and install a new one.

 

[Jim26m]

You're not missing anything.

 

[jviss]

I don't think this is so mysterious, or rocket science.

If you have a check valve separating the cold feed from the hot water circuit, and there's no expansion tank on the hot side, the pressure will increase on the hot side when the water heats up.

Your T&P valve will vent when the P or T increase beyond the set point. The vent should have a hose securely connected, and this should be led to the bilge, and securely fastened.

Replacing the heater won't fix this.

 

[Jim26m]

You are correct, @jviss. However, he can find no evidence of the check valve. He presumes there is one based on the water flow out of the faucet being different between hot and cold.