[Art]

Jeff, bear with me on this explanation. The valve has to be a 75 PSI. It’s purpose is to relieve the excess pressure so the tank doesn’t burst, or more likely have the end caps expand.

What causes it is the expansion of water in the system, and more precisely in the HW tank. From a cold start the HW tank contents are not exerting any pressure on the tank. But our coaches circulate coolant around the HW tank to heat it. Our coolant gets to around 200 degrees so the water in the tank expands, which increases the pressure in the tank potentially.

But there are supposed to be two things in the system to mitigate the potential for an over pressure condition in the tank. The first component is a plastic check valve on the incoming cold water supply to the tank. The check valve is a safety feature that could prevent a large spray of hot water if something should fail on the cold water side so it is needed. But the water expansion has to go somewhere so that valve should have a tiny diameter hole in the valve so as the water expands it can weep back into the CW side.

However, for that to happen the Liberty system should have an accumulator or expansion tank. As the HW expands and weeps back instead of building pressure in the entire system, the accumulator or expansion tank will absorb that pressure. If the accumulator bladder has failed or if the air pressure on the air side of the bladder is gone then the expansion of water has nowhere to go, but to increase system pressure to open the safety valve on the HW tank.

The accumulator tank pressure is set at about 2 PSI more than the pump “on” pressure. Adjust it with the system at zero water pressure and a faucet open. It can be filled with a normal air chuck at a Schrader valve on the accumulator tank.

Some coaches were not equipped with an accumulator tank so you have to be a detective to see if you can find one. If not the accumulator is a tiny one part of the water pump and not serviceable. You likely have one somewhere,m even if it is the accumulator for the RO water supply.

So your pressure temperature valve may be OK, so first make sure your accumulator tank bladder is set at the correct pressure, and also verify the check valve has a tiny hole that is open.

[Eric]

Jon – THANK YOU VERY MUCH

[Chad]

I forgot to mention that the potential water temp of 200 degrees is dangerous. Owners traditionally have almost closed the valves controlling coolant flow into the loop around the tank, but to prevent the water from getting excessively hot that flow has to be so low the tank water temperature doesn’t rise much from coolant heating, or is turned off requiring only electric heat.

On my last two coaches I addressed this by adding a solenoid valve in the coolant line and added a thermodisc snap action thermostat set at 125F. That allows coolant to heat the water, but limits its temp to the same temp as it would get if only the electric heater was used. The much lower water temp is not only much safer, but it minimizes water expansion so the TP valve doesn’t open.

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1984 96" with 8V92TA

(remodeled Liberty Coach)

Greenwood, MO

[John]

Jon: Where and how did you install/mount the thermodisc snap action thermostat. Thanks! Dick

[Jeff]

John a part # I have the same thing when pulling mountain pass temp will get 200 degrees when I stop pop off valve in dripping this trip had to peck it back in I at 8600 feet alt for summer

[Archived]

I used a generic snap action thermodisc I bought from somewhere in the internet.

The Raritan water heater has insulation I slid the thermostat under so it was in contact with the steel tank. It is not secured but was jammed under the insulation and did not seem likely to move.

It is a 125 degree normally closed thermostat that opens at 125. I think the differential was 10 degrees but I cannot remember.

I did not install the thermostat and solenoid valve to stop the TP valve from opening, but that is a side benefit. I wanted to limit the HW temperature because it was dangerous and when our grandson was young and traveled with us I did not want him to accidently scald himself.

[Doug]

high temp is what causes the tp to open up I think mine only dose it when engine over heats water

[DON]

The TP valve likely opens because the hotter the water gets the more it expands so if there is no way to relieve the expansion such as the pin hole in a check valve installed by Liberty it is likely both temp and pressure opening the valve.

[james]

Just shut off the engine loop to the water heater. I did that on just about all of mine due to scalding water risk.That may also take the Webasto loop out to your heater, but electric will work fine.

[rafael]

Another option is a thermostatic mixing valve like this one. Honeywell AM100-UT-1LF. Plumbed in between water heater output and distribution manifold.

[Craig]

All well and good, but it does not answer the issue of pressures and temps opening the valve upon every cold start up.

[Archived]

We had a issue yesterday with Hot Water. We had no cold water only Hot water from both cold and hot water faucets . We did drive 400 miles but we do have the bus valves closed on the hot water loop located next to the radiator. Also did not have either the electric or Aqua Hot on . Any thoughts would be appreciated . This is a Vantare Conversion .

[Art]

How hot is hot? No plumbing system should allow the hot or cold water supplies to join, but the exception is where CW enters the HW tank. That separation is usually provided by a check valve.

Warm cold water is not unusual if the tank gets warm from high ambient temps and a warm bay. What is the water tank temp compared to the CW from the faucet?

[joel]

Jon , So hot you could have a cup of tea from either spigot . Way to hot to shower .Will also add this morning I turned on the elect hot water and all was fine for showers . Both Hot and Cold water was plenty . I guess something on the hot engine water loop must be of issue . I figure I need to trace the line to Aqua Hot and look for a mixing or thermostat . Does that sound like the path to take or would this be something else entirely ?

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1999 XLV X-6872,  liberty #440

[Archived]

If you have a mixing valve that can be the issue. If the water tank is not hot, and you do modulate the HW using a valve that could be failing.

Easiest way to find out is if the water tank is cool, the answer is where the hot and cold come together.