leaking relief valve on water heater

[donradcliffe]

I think a check valve on the inlet of the water heater, as shown in the West Marine adviser post, is pretty common.

Based on the density of water vs temperature, if you heat water from 20C to 60C, its volume will increase about 1.5%, or 0.75L in a 50L water heater. If you want to accommodate that in a nominal 35 psi system without blowing off a 70 psi relief valve, you will need an accumulator with about 0.75L of air.

[steve77]

Originally Posted by sailorchic34

Actually the pump comes on after a few seconds as the pump on set point is lower then the off set point. even with the quart accumultors you should see about 8 seconds before the pump runs.

More then likely, there isn't enough expansion space in the accumulator.

If the accumulator was working properly, the relief valve would not leak. A US relief valve will not leak at 180 degrees F or at pressures normal in a marine or typical land side system. That the second relief also leaks points to a lack of thermal expansion space in the water system. The T&P relief valves generally have very high reliability. Two reliefs having the same issue, points to something other then the relief valve.

I have 40+ years designing plumbing systems in building projects. Some had over $40 million in plumbing costs.

A $40 1 gallon expansion tank from the big box store, will solve your problem.

I find that the quart (liter) size marine expansion tanks to be marginal at best for a marine water heater, that can be heated to 160 degrees F + via engine loop.

I apologize if you thought I was questioning your credentials or experience. That was not my intent.

The water will run a bit over 11 seconds before the pump begins running. I just don't believe that there is a problem with the accumulator. I have a small bicycle pump that I keep near the accumulator. When the pump begins to cycle excessively, I go through the process you mentioned earlier to restore the air bubble.

The Isotherm manual states "A small quantity of water can drain from the relief valve when the water is heated. The water expands during heating. This is a normal situation and indicates the system works properly."

Again, I am seeing much more than a "small quantity of water".

With the performance of the pump that I am seeing, do you still believe that the accumulator is insufficient to handle the thermal expansion? Thanks!

I can try to find a source for a larger accumulator but it is a bit more difficult here than in the US. I will check around. Thanks!

Steve

[steve77]

Originally Posted by sailorchic34

A check valve on the cold water inlet is not required or wanted in the typical marine water heater. Well Typical US style Marine water heater.

If there is a non-return valve as part of the tempering valve assembly then you will need to add a accumulator on the discharge of the water heater, per the west marine diagram.

Thanks. I agree that there is no reason for a nonreturn valve in our system. If anything, all it will do is cause the problem I am seeing.

I don't know a lot about tempering valves. Is it common for one to incorporate a check valve?

I reread the manual, particularly looking for any mention of accumulators and whether they should be installed upstream or downstream of the heater. There is absolutely no mention of them. The piping diagram shows the freshwater tank, pump, engine, faucets, etc., but no accumulator.

Steve

[sailorchic34]

The accumulator can be on either side of the water heater, hot or cold. Normally I would not use a check valve on a small water heater system even with a tempering valve. If the accumulator is between the water heater and cold water, or just before the take off of the cold to the tempering valve a check valve is not required.

You will want to find a Amtrol st-5 (or equal) On ebay here https://www.ebay.com/p/Amtrol-140n43...4754873&chn=ps or most hardware stores would have it.

Allows for nearly a gallon of acceptance and it can be located anywhere down stream of the pump and it will prevent the relief from popping (provided no check valve on the inlet of the water heater. The smaller liter size accumulators must marine stores sell are just a tad too small for a water heater that can heat water to a 140 degree F rise (to 180F). I had one fail on me as well.

[steve77]

Originally Posted by donradcliffe

I think a check valve on the inlet of the water heater, as shown in the West Marine adviser post, is pretty common.

Based on the density of water vs temperature, if you heat water from 20C to 60C, its volume will increase about 1.5%, or 0.75L in a 50L water heater. If you want to accommodate that in a nominal 35 psi system without blowing off a 70 psi relief valve, you will need an accumulator with about 0.75L of air.

Thanks, Don. We have a 20 liter tank, so 0.3 liters of expansion from 20 to 60 degrees C.

Our freshwater pump shutoff is set for 45 psi, plus or minus 5 psi. The relief valve on the water heater is 100 psi.

Steve

[transmitterdan]

What is the pressure in the system when the fresh water pump cuts off? If you don’t know and can’t measure it then consider adjusting the pump cutoff switch pressure down quite a bit. Almost all fresh water pumps have an adjustment for the stopping pressure. Some have two adjustments for start and stop pressure. By lowering the system standing pressure it should reduce pressure on the heater relief valve.

[hoolie]

Our tank has a built-in check valve on the cold water inlet - it's not obvious externally. Our tank was bought in the UK and AFAIK such a check valve is normal in the European market.

Obviously with a check valve an accumulator on the cold inlet side does nothing except buffering the water pump. It has to go on the hot water outlet to deal with expansion. Expansion isn't only when heating up from cold - if you use hot water then without an accumulator the pressure relief valve will continually "dribble" as the water comes back up to temperature.

[steve77]

Originally Posted by hoolie

Our tank has a built-in check valve on the cold water inlet - it's not obvious externally. Our tank was bought in the UK and AFAIK such a check valve is normal in the European market.

Obviously with a check valve an accumulator on the cold inlet side does nothing except buffering the water pump. It has to go on the hot water outlet to deal with expansion. Expansion isn't only when heating up from cold - if you use hot water then without an accumulator the pressure relief valve will continually "dribble" as the water comes back up to temperature.

Thanks. I agree with you totally. I'll check with Isotherm and see if there is a check valve anywhere on the water heater.

Steve

[steve77]

I checked with Isotherm and they confirmed there are no check valves of any type internal to our water tank. This makes perfect sense to me as I can't think of a single reason to have check valves unless you are connected to a shoreside water supply.

So, more pertinent to my problem, there is nothing to prevent our accumulator from absorbing whatever water expansion there may be from the water heater.

I will try to make it to the local equivalent of Home Depot on Monday to see if I can get a larger accumulator. Thank goodness the Italians use imperial plumbing fittings so I don't have any issues with making things compatible.

Steve

[donradcliffe]

A word of warning about plumbing in Europe. The bloody British have been there with their BSP untapered fittings. For instance, every pipe joint I saw in Israel has some sort of string wrapped in the thread to seal it, rather than a proper NPT taper.

[steve77]

Originally Posted by donradcliffe

A word of warning about plumbing in Europe. The bloody British have been there with their BSP untapered fittings. For instance, every pipe joint I saw in Israel has some sort of string wrapped in the thread to seal it, rather than a proper NPT taper.

Yes, I found that out. The fittings are in inches, but straight. That's been true in Portugal, Italy, and Greece, and probably most of the rest of Europe.

Cheers!


Steve

[transmitterdan]

There are basically 3 things that can cause the relief valve to leak:

1) faulty valve
2) water is too hot
3) pump pressure is too high

You tried a different valve. How do you know it’s not one of the other two?

In my opinion a bigger accumulator will not fix either of these issues.

[steve77]

Problem solved.

I purchased a 5 liter accumulator. Our accumulator is mounted vertically with the inlet at the bottom. When I removed the existing 2 liter unit I had the wet vac going to suck up the water that I expected to come out of the bottom. Surprisingly, very little water came out.

Wait a second, I says, the water heater is mounted higher than the accumulator. There should have been 20 liters of water gushing from the open tee in the hose.

Less than 5 minutes later I found the check valve mounted near the supply to the hot water tank. As the water heats and expands, it couldn't go out the discharge since the faucets were closed and it couldn't go out the inlet because of the check valve. Thus, the only possible path for the water to expand was through the relief valve.

I removed the check valve and this solved the problem. The accumulator now handles the expansion from the heated water. I did go ahead and install the larger accumulator, but only because I had already bought it. The problem was solved as soon as I removed the check valve.

Again, for our installation, which is the accumulator located between the water pump and water heater, a check valve is not needed.

Steve

[donradcliffe]

Physics wins again!

[deluxe68]

Originally Posted by steve77

Problem solved.

I purchased a 5 liter accumulator. Our accumulator is mounted vertically with the inlet at the bottom. When I removed the existing 2 liter unit I had the wet vac going to suck up the water that I expected to come out of the bottom. Surprisingly, very little water came out.

Wait a second, I says, the water heater is mounted higher than the accumulator. There should have been 20 liters of water gushing from the open tee in the hose.

Less than 5 minutes later I found the check valve mounted near the supply to the hot water tank. As the water heats and expands, it couldn't go out the discharge since the faucets were closed and it couldn't go out the inlet because of the check valve. Thus, the only possible path for the water to expand was through the relief valve.

I removed the check valve and this solved the problem. The accumulator now handles the expansion from the heated water. I did go ahead and install the larger accumulator, but only because I had already bought it. The problem was solved as soon as I removed the check valve.

Again, for our installation, which is the accumulator located between the water pump and water heater, a check valve is not needed.

Steve

They put check valves in the input to the water heater for a reason.