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Old 16-04-2018, 06:02   #1
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leaking relief valve on water heater

My Isotherm water heater (boiler) is leaking water through the relief valve. It only leaks when the heater element is on. Depending on the amount of hot water usage, and thus the amount of time the heating element is on, this leakage is half a liter to a liter per 24 hours. This water leaks through the drain hose to the bilge, and it was from a running bilge pump that I tracked it back to the relief valve.

With the water heater circuit breaker turned off there is absolutely no leakage.

I contacted Isotherm and they sent a replacement relief valve, however this did not solve the problem. I am still accumulating water from the drain hose (the amount in the previous paragraph is with the replacement relief valve).

The Isotherm rep said it is normal for a "little" leakage when the water heater is first turned on. He agrees that the amounts I am seeing are excessive.

However, since the relief valve has been replaced he thinks something else in the system is causing this leakage. However, I am at a loss as to what else could cause this.

Any suggestions? Thanks!

Steve
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Old 16-04-2018, 06:16   #2
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Re: leaking relief valve on water heater

Quote:
Originally Posted by steve77 View Post
My Isotherm water heater (boiler) is leaking water through the relief valve. It only leaks when the heater element is on. Depending on the amount of hot water usage, and thus the amount of time the heating element is on, this leakage is half a liter to a liter per 24 hours. This water leaks through the drain hose to the bilge, and it was from a running bilge pump that I tracked it back to the relief valve.

With the water heater circuit breaker turned off there is absolutely no leakage.

I contacted Isotherm and they sent a replacement relief valve, however this did not solve the problem. I am still accumulating water from the drain hose (the amount in the previous paragraph is with the replacement relief valve).

The Isotherm rep said it is normal for a "little" leakage when the water heater is first turned on. He agrees that the amounts I am seeing are excessive.

However, since the relief valve has been replaced he thinks something else in the system is causing this leakage. However, I am at a loss as to what else could cause this.

Any suggestions? Thanks!

Steve
Steve--

Have you thoroughly vented the air out of the tank? New Pressure Relief Valves sometimes take a few cycles to "seat" and so leak somewhat after their initial installation (BTDT) but if there's a good deal of air trapped in the tank, the expansion of that air as the water heats could trip the valve as, normally, Pressure Relief Valves on boat water heaters are only rated for 75PSI which is much lower that that on one's home water heater. You may need to manually open the vent and let it run until it stops "sputtering". (We just went through this with a Raritan Water Heater aboard our boat.)

FWIW...
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Old 17-04-2018, 00:42   #3
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Re: leaking relief valve on water heater

Thanks for the reply.

The tank is a horizontal unit and the connections for water in and water out of the heater are near the top of the tank. There are no provisions for venting air from the tank. However, I refilled the tank a month ago after replacing the relief valve, so I would assume most of the air would have worked its way out.

I understand that if the heater was water solid, then heating the water could result in fairly high pressures from the attempt of the water to expand. This is what the Isotherm rep has said. In this case, an air bubble in the tank would help minimize the pressure by allowing the water to expand into the air space.

This same logic holds true with the accumulator I have installed on the inlet side of the water heater. If the tank is really seeing such high pressures from water expansion then I would think that the air in the accumulator would help minimize this by allowing somewhere for the expanded water to go. There is nothing preventing water from the tank expanding "backwards" to the accumulator.

According to the Isotherm manual the relief valve is set for 100 psi. I just don't see how I'm getting anywhere near that pressure.

Thanks!

Steve
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Old 17-04-2018, 08:23   #4
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Re: leaking relief valve on water heater

Install an accumulator (expansion tank) on the hot or cold water side of the water heater. Cold water expands when heated. Without an accumulator (expansion tank) the relief will pop and dribble. Quite normal to do so.

The 1 gallon type expansion tank for $40 at the big box hardware stores works well and are less then 1/2 the price of a "Marine" ones.
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Old 17-04-2018, 08:40   #5
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Re: leaking relief valve on water heater

Possibly just a weak relief valve that is temp sensitive? Have you tried another one? Even new ones can be bad. There is no excuse for one to leak even a drop if you have an expansion tank.
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Old 17-04-2018, 13:04   #6
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Re: leaking relief valve on water heater

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Originally Posted by sailorchic34 View Post
Install an accumulator (expansion tank) on the hot or cold water side of the water heater. Cold water expands when heated. Without an accumulator (expansion tank) the relief will pop and dribble. Quite normal to do so.

The 1 gallon type expansion tank for $40 at the big box hardware stores works well and are less then 1/2 the price of a "Marine" ones.
Thank you. Yes, there is an accumulator on the cold water inlet side of the hot water tank. As I stated earlier, I cannot understand how the pressure in the hot water tank could get so high since there is an accumulator with an air bubble in it to absorb any expansion in the water as it heats.

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Old 17-04-2018, 13:08   #7
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Re: leaking relief valve on water heater

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Originally Posted by US1Fountain View Post
Possibly just a weak relief valve that is temp sensitive? Have you tried another one? Even new ones can be bad. There is no excuse for one to leak even a drop if you have an expansion tank.
I'm thinking that you are correct. Yes, Isotherm supplied a new valve when I contacted them with this problem I am still seeing this leakage with the replacement valve.

At present, my leaning is to contact Isotherm again and tell them that the replacement valve was bad, and I need another replacement.

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Old 17-04-2018, 13:27   #8
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Re: leaking relief valve on water heater

Check that your existing expansion tank is not water logged or rubber diaphragm is torn/failed. I had a jabisco plastic tank type fail at the the diaphragm which causes it not to work. fix is to install a new expansion tank, or bleed water from the existing one.

to bleed water, turn pump off. open sink faucet (hot side or hot and cold side), attach bike pump to valve on expansion tank and pressurize expansion tank to 20 psi ish (+/- 5 psig). That should keep it working for a few days if the diaphragm is torn. If it continues working, then all is OK, if not replace the expansion tank.
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Old 17-04-2018, 16:48   #9
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Re: leaking relief valve on water heater

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Originally Posted by steve77 View Post
Thank you. Yes, there is an accumulator on the cold water inlet side of the hot water tank. As I stated earlier, I cannot understand how the pressure in the hot water tank could get so high since there is an accumulator with an air bubble in it to absorb any expansion in the water as it heats.

Steve
There should be a backflow valve keeping the water in the heater from backing up into the expansion tank. The relief valve will open if the pressure or temperature (TP) get too high.

1. First, thing is to find out what the ratings are on your TP valve.
2. Look at your water heater and find out what the temperature is set at. If it does not indicate numbers, then get a thermometer and test the temperature at a faucet.
3. After the heater has been on a while, open the TP valve. If steam comes out then your water heater may not be cycling off.

There are two safety measures built in, the internal temperature sensor and the TP valve. The old water heater on my boat had a failure and the heaters would not turn off. Your water temperature should not be over 120.
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Old 17-04-2018, 17:09   #10
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Re: leaking relief valve on water heater

An addendum to my comment about 120 degree water, some marine heaters are much hotter AND take nearly steaming hot water from the engine. Here is a diagram showing a non-return (backflow) valve.

https://www.westmarine.com/WestAdvis...hwater-Systems
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Old 18-04-2018, 00:57   #11
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Re: leaking relief valve on water heater

Following as I am just now installing a new Isotemp 4 gal unit. Thanks
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Old 18-04-2018, 10:27   #12
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Re: leaking relief valve on water heater

Quote:
Originally Posted by sailorchic34 View Post
Check that your existing expansion tank is not water logged or rubber diaphragm is torn/failed. I had a jabisco plastic tank type fail at the the diaphragm which causes it not to work. fix is to install a new expansion tank, or bleed water from the existing one.

to bleed water, turn pump off. open sink faucet (hot side or hot and cold side), attach bike pump to valve on expansion tank and pressurize expansion tank to 20 psi ish (+/- 5 psig). That should keep it working for a few days if the diaphragm is torn. If it continues working, then all is OK, if not replace the expansion tank.
I believe the accumulator is good and not water solid. When I run the tap, the water will run for a few seconds before the pump kicks on. The time depends on how much water has been run recently.

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Old 18-04-2018, 10:43   #13
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Re: leaking relief valve on water heater

Quote:
Originally Posted by deluxe68 View Post
There should be a backflow valve keeping the water in the heater from backing up into the expansion tank. The relief valve will open if the pressure or temperature (TP) get too high.

1. First, thing is to find out what the ratings are on your TP valve.
2. Look at your water heater and find out what the temperature is set at. If it does not indicate numbers, then get a thermometer and test the temperature at a faucet.
3. After the heater has been on a while, open the TP valve. If steam comes out then your water heater may not be cycling off.

There are two safety measures built in, the internal temperature sensor and the TP valve. The old water heater on my boat had a failure and the heaters would not turn off. Your water temperature should not be over 120.
I'm not sure what a TP valve is. If you are referring to the relief valve, it is set to 100 psi per the Isotherm manual. I believe it opens on pressure only. The manual has no mention of a temperature setting for this valve to open.

There are no numbers on the temperature setting valve on my water heater. It is not possible to measure the temperature setting at the tap since this heater incorporates a thermostatic mixing valve at the heater to mix cold water with the hot to prevent scalding. As you mention in your follow-on post, the water temperature in the tank is certainly above 120 degrees F when the engine is used to heat the water. This is the primary reason Isotherm incorporates the thermostatic mixing valve.

The heater is cycling off when the water reaches proper temperature. I have confirmed this by checking AC power usage and noting when the unit stops drawing power.

But let's talk about this check valve to keep water from backing up to the expansion tank. I do not have one external to the water heater, and I don't see a reason for it. Would this be in the water heater? What is the purpose?

Thanks!

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Old 18-04-2018, 10:59   #14
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Re: leaking relief valve on water heater

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.
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Old 18-04-2018, 11:02   #15
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Re: leaking relief valve on water heater

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But let's talk about this check valve to keep water from backing up to the expansion tank. I do not have one external to the water heater, and I don't see a reason for it. Would this be in the water heater? What is the purpose?
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.
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