Hot water in toilet tank

Recently, our toilet has been occassionally filling with hot water instead of cold. This primarily happens when the toilet hasn’t been flushed in a few hours (such as first thing in the morning). As we continue to flush, the water goes from hot to warm to cold, and the flushes stay cold until the toilet isn’t used again for a few hours. We live in a condo building, and have been advised by the building’s plumbers that this is likely caused by faulty mixing valves which are located behind the shower faucet, which is causing the hot and cold water supplies to get “mixed upâ€. They did not examine anything, just simply stated that this is what is causing the problem and quoted around $1200 to replace the valves. However, if this was the case, wouldn’t the water be mixed up for other things in the bathroom, such as our shower, bathtub, sink, and washing machine (located in the bathroom), and would this occurrence not happen at all times, not just when the toilet hasn’t been used for a few hours? I am not sure if this is pertinent, but when the faucets in the sink and shower haven’t been used for a few hours we get only hot water from them (no cold) for a few seconds when the taps are initially turned on. We have not done any work in our bathroom recently, so it wouldn’t be as a result of that. Any advice would be most appreciated as I would like to have some idea of what could be causing this before having a plumber in. Thanks!!

Does you system have a hot water circulator? If it does and does not have a dedicated return line, then this could cause that situation.

All it takes is one faucet or shower valve that is not working properly to allow a cross-connection between the hot and cold. This only applies to single handle faucets or valves, but in the case of a shower, nearly all of them are now because of the codes. It could be anywhere. Do the other people in the condo complex have similar problems? If they do, it may be a condo association problem rather than an individual's.

If the pipes aren't insulated, and are run near other things that are hot, you could get the cold water quite warm, especially if your supply pipes run through the attic. Insulation might help a little, but all that does is slow the movement of heat, it doesn't stop it.

Depending on how hot the water going to the toilet is, it is potentially able to crack the porcelain, especially if the place is air-conditioned. The tank (eventually) gets to say the low 70's, then you flush and refill with (who knows how) hot water. The rapid temperature change is not kind to ceramics. It would have to be pretty radical temperature difference, but it is possible.

lemosa said:

Recently, our toilet has been occassionally filling with hot water instead of cold.

Click to expand...

There have been a number of people recently on this forum who wish they had this problem. Once you figure out what's causing it, let everyone know, so they could have hot water in their toilet as well.