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Old 12-01-2018, 08:36   #1
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Hot water heater relief valve opens

I recently installed a Seaward 6 gal 110V water heater, which I purchased used from a friend. It worked fine for a few months, but now once it gets up to temperature, the relief valve opens every so often, releasing some VERY HOT water into the bilge. The water that comes out of the faucet is almost scalding. I don't leave the pressure water on unless I am using it, so once the pressure is released, water does not come out of the valve again until I use more water and the tank heats up the newly arrived water.

I am wondering if the problem is the thermostat. The heater has NEVER been run dry, and the element is clearly working. It seems like the thermostat is just not shutting to let the system know that it should stop heating (at least that is what makes sense to me).

Am I on the right track? How can I find out if the thermostat is bad? Thanks for any help!
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Old 12-01-2018, 09:24   #2
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Re: Hot water heater relief valve opens

I had a similar issue. However it turned out my water pressure pump was to high. In your case try turning down the thermostat and see if that helps. The hotter the temp the more pressure and might be just enough to trip it.
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Old 13-01-2018, 04:35   #3
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Re: Hot water heater relief valve opens

Likely the Thermostat or T&P Valve is/are faulty. Most likely the Valve.
Sure Marine Service, Inc. | Seaward Water Heater Parts
https://www.defender.com/pdf/Seaward...s_Install2.pdf
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Old 13-01-2018, 06:32   #4
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Re: Hot water heater relief valve opens

Quote:
Originally Posted by Mariellec View Post
I recently installed a Seaward 6 gal 110V water heater, which I purchased used from a friend. It worked fine for a few months, but now once it gets up to temperature, the relief valve opens every so often, releasing some VERY HOT water into the bilge. The water that comes out of the faucet is almost scalding. I don't leave the pressure water on unless I am using it, so once the pressure is released, water does not come out of the valve again until I use more water and the tank heats up the newly arrived water.

I am wondering if the problem is the thermostat. The heater has NEVER been run dry, and the element is clearly working. It seems like the thermostat is just not shutting to let the system know that it should stop heating (at least that is what makes sense to me).

Am I on the right track? How can I find out if the thermostat is bad? Thanks for any help!
Mariellec--

If you review the Owner's Manual on the Seaward Water Heaters (here) you will find, on the top of page 3, a Notice to the effect that, during initial operation, the pressure relief valve may tend to "weep" until it wears itself in and "seats". Accordingly, the instructions indicate that a drain line should be provided to an area where the discharge will not cause damage. Frankly, I wouldn't be too thrilled with such a provision and would not have selected a unit with that proclivity but its what you've got so you may have to endure for awhile. If the condition persists, however, the Relief Valve may need be replaced, if so, I would proceed apace with the Company as the warranty on that device has a limited time period.

FWIW...
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Old 13-01-2018, 07:23   #5
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Re: Hot water heater relief valve opens

Measure temperature of hot water out of tap. If WH is operating on electric, and temperature is much above 140 F your thermostat is bad. If heating by engine, you will likely be higher temp near equal to engine coolant temperature. The T&P relief valve usually doesn't open until temperature is very high at 210 F. If temperature is that high, thermostat really needs to be replaced. If T&P discharging at lower temperature than 210 F, need to replace T&P valve.
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Old 13-01-2018, 07:41   #6
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Re: Hot water heater relief valve opens

KISS. Before you replace the relief valve, just turn the electricity off after 15-20 minutes. Don't exercise the valve since sometimes it doesn't reseat. It doesn't take water too long to get hot in those heaters. I have had them for 20 years.
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Old 13-01-2018, 08:33   #7
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Re: Hot water heater relief valve opens

If there is no air in the system and you start with cold water, the water expansion will increase pressure until the relief valve lifts-there are check valves in your pump and there is really no other place for the hot water to go until you open a tap.

My original water heater never completely filled with water, so the remaining air in the heater acted like a cushion. When I replaced it with a different model I would get some relief valve discharge until the system warmed up. If you don't like it, putting an accumulator in the hot water line somewhere would probably solve the problem.
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Old 13-01-2018, 08:44   #8
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Re: Hot water heater relief valve opens

I like to sail but I also have residential rentals. You are using 110v so you should keep the temperature low. In my rentals I keep the temp 110 to 120F to avoid scalding. The maxium allowed is 140F for liability reasons. 140F will scald in a matter of 3-5 seconds, 120F about 45 seconds and 110F not really at all. These are just a general guide I'm not a doctor or engineer. What I'm trying to say is that is too hot for a guest or a child that may be visiting or sailing with you.

It sounds like the thermostat allows the initial heating to go to the boiling point before shutting down. If I'm reading between the lines you are suggesting there is no adjustment on the thermostat. If you can't lower the temperature replace the thermostat. The relief valve is just doing what it's supposed to do.

Good Luck!
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Old 13-01-2018, 09:05   #9
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Re: Hot water heater relief valve opens

My boat has a small tank with high temperature setting to provide sufficient hot water. I’m installing a tempering valve to prevent scalding, lots of brands out there, I think Shurfow makes one, look on defender or Fisheries Supply or McMaster-Carr.
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Old 13-01-2018, 09:20   #10
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Re: Hot water heater relief valve opens

Some good points already made, the first thing I would do is set the thermostat lower if accessible, the second thing is most important never leave the hot water heater on and turn the pump off, if the tank runs dry you will have to replace the element, good luck
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Old 13-01-2018, 09:51   #11
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Re: Hot water heater relief valve opens

A final note:

There are two Thermostats on your water heater: A "High Temperature Limiter" which, when tripped by overheating must be reset manually; and, a standard Thermostat that cycles the heating element on and off once the pre-set temperature, which I believe is fixed at 140 F and cannot be adjusted, is reached. For preventing scalding risk, the manufacturer suggests the use of its mixing valve (here) with which one can pre-set the temperature of the discharge water. Note, however, that the mixing valve should be adjusted based upon the hottest water the water heater is likely to produce, either from the electric heating element or from the engine coolant heat exchanger.

FWIW...
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Old 13-01-2018, 11:01   #12
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Re: Hot water heater relief valve opens

With all the previous good advice, it is now safe to ask the question, Why are you heating hot water? The thread title could explain the problem.
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Old 13-01-2018, 12:05   #13
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Re: Hot water heater relief valve opens

Quote:
Originally Posted by Dennis.G View Post
Measure temperature of hot water out of tap. If WH is operating on electric, and temperature is much above 140 F your thermostat is bad. If heating by engine, you will likely be higher temp near equal to engine coolant temperature. The T&P relief valve usually doesn't open until temperature is very high at 210 F. If temperature is that high, thermostat really needs to be replaced. If T&P discharging at lower temperature than 210 F, need to replace T&P valve.
My husband the plumber says this is what he would do. Also, it's worth a look to see if the temperature control Thermostat is adjustable, that might solve it.
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Old 13-01-2018, 12:47   #14
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Re: Hot water heater relief valve opens

Hi , If the hot water is coming out scalding hot thats way to hot , you need to stop using untill you find out why ,
First is the thurmostat stuck ? as they dont normaly go from OK to SCALDING with out some one turning them up ,,

grab a thermomiter and check the temp so you know ,,,
also has the Tank a blending valve installed ,, if not sounds like a great time to put one in ,,

Its a long way to the hospital some times
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Old 13-01-2018, 19:16   #15
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Re: Hot water heater relief valve opens

First order of business is to understand the purpose of the t&p. It is to keep the water heater from becoming a bomb. It functions in two ways one if pressure rises above the set amount, residentially usually150 psi (sorry I don't know metric equivalent) on boats I think they might be set at 125 psi. In is max legal household pressure is 80psi, pumps on boats will be considerably less. Thermal expansion of heating water in a closed system can cause a little spike. This would be seen as weeping from valve not gushing. Steam pressure in the system is more akin to an automotive radiator overheating and blowing steam. Is this occurs on boat, get off and cut power, if that is not an option. Leave water pump on to replace steam with cold water, turn off power to tank. Run hot water taps. Stay away from tank until it cools. 6 gallons of high pressure steam bursting the tank could destroy a 30 foot boat, or if lucky just punch a 12 inch hole in it on its way out. The second operation of t&p by the way is to sense boiling water and relieve in hopes of cooling tank before steam builds.
Either way if it leaked more than a cup of hot water or steam shut it down until it can be checked or just replace the damn thermostat.
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