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Water heater over pressure

If I leave water heater running on thermostat , I notice an increase in water pressure at inlet point in wet bay , I was advised to drain hot water tank to reastablish the air expansion head within the tank . Tried that and problem persists , is this a thermostat problem
Jimmy
2003 U295 3620

Re: Water heater over pressure

Reply #1 –
You may want to install a pressure gauge to see how much pressure is there.  Check the outlet of your relief valve and see if it is lifting.  That relief valve should protect you from high pressure due to a failed thermostat.  You may also just have a leaky connection somewhere.  Have a great day  ----  Fritz
Fritz & Kathy Johnson
1991 36'

Re: Water heater over pressure

Reply #2 –
An accumulator in the fresh water system will mitigate the problem. Air space almost anywhere in the system will help moderate the high pressure caused by the expansion of water as it heats.

Many people remove the accumulator when they install a variable speed water pump. We left ours in place and the system works well. I have heard that some variable speed pumps don't play well with an accumulator. Ours works well.

Indeed, check the relief valve on the water heater.

If the behavior is the same whether on electric or gas, the thermostat is probably not the cause of the problem. Our water heater uses separate thermostats for electric and gas. Yours may be different. Ours is a 1997 Atwood three way (electric, gas, heat from engine coolant).
J D Stevens
1997 U295 CAI 36' Build #5085
2002 Subaru Outback
Motorcade 16869
Bellville, TX

Re: Water heater over pressure

Reply #3 –
I had the same problem after I took out the accumulator tank and the water heater safety valve would dribble.  Installed new accumulator tank and it's never happened again.  Variable speed pump works just fine with it.
John Fitzgerald
1991 U300 (SAI) Side Aisle Island Bed 40'
Detroit 6V92 with Allison Retarder
Meridian (Boise), Idaho

Re: Water heater over pressure

Reply #4 –
Water expands when heated, increasing pressure on the whole plumbing system, showing up at all faucets or water hose inlet.

Turning off hot water tank when not using it, allows water to cool, which causes greater expansion pressures. We now leave tank on electric heat all the time to reduce the amount of expansion at one time. Every time we flush toilet or run water for a moment during the day or night, we remove the pressure build up.

Re-establishing air pocket at top of tank does very little. Having an expansion tank also does little to reduce high pressure created by heating water.

Re: Water heater over pressure

Reply #5 –
The reason to have an expansion tank is to prevent the build up of pressure in the system . Air in the hot water heater will prevent this pressure build up but over time the air will mix with the flow of water through the tank and soon you will only have water in the tank. If your expansion tank isn't preventing the build up in pressure its diaphragm has ruptured and the tank must be replaced.Without an expansion tank the only thing protecting your hot water system is the safety valve on the water heater. With over pressure build up the safety valve will start to simmer and leak. At this point the safety valve will have to be replaced. Gam
joseph gambaro
1999 U295 36'

Re: Water heater over pressure

Reply #6 –
JD, Newer electric & gas Atwood water heaters use the regular front thermostat for both electric & gas. Electric uses a 12-volt coil relay to power heating element. Control board is different on these heaters. We replaced our original heater with newer style.

Re: Water heater over pressure

Reply #7 –
Not sure if I have an expansion tank , I replaced the original variable speed pump with direct replacement , but did not see any expansion tank ?
Jimmy
2003 U295 3620

Re: Water heater over pressure

Reply #8 –
Earlier coaches had fixed displacement/speed water pumps and used expansion tanks, which took up room, to keep pump from cycling off & on with low water flows.

Later coaches had variable speed water pumps which were designed to slow down on low water flows, reducing the pump cycling, so expansion tanks were not needed as much.

But adding an expansion tank anywhere in the coach on any water line will give an additional space for expanding hot water. Pressures will still rise somewhat within the plumbing.

We find that by using our water during the day & night, high pressures are being continuously relieved. We do not believe in leaving coach without turning off water pump as higher pressures do put a stress on all plumbing fittings. We also never connect a city water hose, except to fill tank. City water pressure can surge at any time, and turning off city water when leaving coach is not as easy as turning off water pump switch.