Call Moen and see what they say. Some manufacturers are generous with providing replacement parts. On the other hand, a new cartridge after 19 years is not a bad service life and buying a new one shouldn't set you back very much.

Moen will send you a new cartridge. Have the faucet model number handy when you call them. Also any store that sells moen should have replacments. Just bring in the old one and they usualy just hand you a new one to match it.

If the problem persists, then you probably have a water meter or pressure regulator with a check valve/backflow preventer, and no expansion tank on your hot water. Because the water can't flow back towards the supply, the hot water starts to creep over to the cold side.

If you do have an expansion tank, the bladder inside has probably failed.

Thanks very much for the replies. I have since checked the warranty page of Moen and it says the warranty applies to the original owner, is valid for purchases after 1995 and receipt is required. I can't meet any of those 3 requirements, so I will buy a new cartridge - indeed I can't complain about a 19yr service life.

What pjb999 said concerns me some because I am wondering if/worried that this is a symptom of a larger problem, because, after all I would normally not get hot water immediately from my hot water tap as the sink is still at least 30 feet from the hot water heater.

I am certain that the hot water heater is 19 years old. Can an aging hot water heater cause the pressure problem leading to the leakover from hot-to-cold? Again can't complain about a hot water heater living that long, just don't know how to tell when it is on its last legs. Its a pretty standard 40-gal gas-fired heater, if that matters. I am not aware of it having an overflow tank, just a press relief safety valve going to a pipe that would dump the water into a drain line.

A couple weeks ago I posted here that I was getting hot water from cold setting on my single-handle faucet, but just briefly. I replaced the cartridge but that did not help. After further sleuthing, I discovered that I had a leak in the hot water line under my slab foundation. I called a plumber who had special leak detection equipment, but he ended up just running a liner through my line for which you need not be concerned about the exact location of the leak -- we could tell it was between my utility room and kitchen from the warm spots on the tile floor.

It took several days for the water to drain/cool under the foundation, but apparently it was that pool of hot water that was heating the cold water line on the way to the sink.

We don't know for sure, but the plumber said in this area such leaks are often from moles chewing -- the pipe in question was plastic. We have seen evidence of mole activity in our yard and under our house -- recently we remodeled our master bath and saw sand under the bath tub that had been pushed up through the opening for the drain pipe by the critters.

After this and our cat getting skunked, it is open season on varmints here!!!