Hot water in toilet

I recently purchased 2002 Four Winds Windsport Class A motorhome. On a recent weekend trip when flushing the toilet, hot water would flow in it instead of cold water. We were connected to city water at the campground. This only happens when connected to city water, not when using the water pump. The pressure at the campground wasn't very high. We were at a campground a few weeks earlier with no water hook-up and used the toilet with no problem. I'm guessing that the hot water is coming from the water heater inlet because of the low pressure of the city water. The water lines all seem to be connected properly. I'm thinking a check valve at the inlet of the water heater might solve the problem. Does this make sense? Any info would be appreciated.


Senior Member
Hot water in toilet

Keep in mind that the hose from the water source to the trailer is subject to heat and sun, and possibly some other part(s) of the water delivery system. What was the outside temperature at the time this happened? Was the sun shining on the hose or was any part of the water system exposed to the air?

When I go to water plants, I have to let the hose run for a couple minutes to avoid 'scalding' the plants :)
Hot water in toilet

Hertig has a good point. You may have been getting hot water from the hookup, but just enough for a good flush, then cool at the sink.
A little warm water backfeeding into the cold line near the water heater is normal. A check valve would create more problems than it would solve as the water has to go somewhere when it expands as it is heated.
The other thing that comes to mind is do you have a single-handle faucet on the sink or shower? When they get worn, they will sometimes crossfeed the hot and cold water. Repair kits are fairly cheap and not too hard to install for common brands.
Hot water in toilet

Thanks hertig & ed,
It is definitely not warm from the sun. The weekend was very cool. Also, the theory about the check valve makes sense. I think I'll scrap that idea. There is a single faucet in the kitchen sink which is very close to the water heater. I'll check that out. Again, thanks for the legit responses.


Senior Member
Hot water in toilet

Actually, many RVs today have a check valve on the cold water inlet line to the water heater, as mine does. That has become very common. A properly operating water heater has an air space in the top of the tank as the outlet is below that point to allow for that space. It is there to allow for contraction and expansion of the water as the temperature changes.

I suspect that the source of your hot water flush is that you recently used the outside shower head and then turned the water off on the hand held head and left the two valves that supply it both open. Because you have a check valve in the inlet line to the water heater, the pressure on the hot water side is higher than at the cold when you first turn the water on. That extra pressure could cause hot water to flow through the open hot of the outside shower, into the open cold and then to the toilet. You would not likely see it at the sink because the shower is probably much closer to the toilet than to the sink and as the pressure equalized the cross flow will drop or stop. I suggest that you go out and check the valves for your outside shower head.

If it is not the outside shower, then check the inside shower as it could cause the same problem, but is less common.