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Cold Water Contamination with Hot Water

I have a 14 year old home with a dedicated hot water recirculation system using a plumbed return line. Recently I began to notice tht the cold water would run cold then warm up to hot and then after 30 seconds cool off again. This happened on two handle lavs as well as single handle showeer lines. Even the toilet water chamber will be warm on the occasion when I had to clean sediment from the tank valve. I had the water heater replaced a week ago along with a new pump that is on a timer. Thought this might help but no. Another plumber suggested that the cartridge on the showers may be bad and allowing cross contamination of the cold with hot water. I'm not sure this makes sense but I have the new cartridges on the way and I will change them out as it has been 14 years. There is a check valve on the pump sytem but the recirc line empties into the cold supply of the HW tank after the check valve and I wonder whether the hot recirc water is getting diverted into the cold feed. Hard to imagine as it is a long way back up the cold to the lavs and toilets and showers throughout the house.

Any thoughts?

Re: Cold Water Contamination with Hot Water

When your new cartridges arrive, install them and see what happens. If your problem at the faucets is solved, then you'll still have to deal with the toilet tank supply.

Re: Cold Water Contamination with Hot Water

I'm not sure what you mean by the return line enters into the tank after the check valve on the cold side. A picture would help. The proper way to pipe it is to hook the return line into the bottom of the tank with a check valve. This is done by removing the drain valve and installing a tee at the bottom of the heater using the branch of the tee for the recirculating line and the other for the new drain.


Re: Cold Water Contamination with Hot Water

Thanks for the responses. The idea of bringing the return line to the bottom with a check valve makes sense. What is intriguing is that for about 13 years the system was OK, despite the hookup and then recently changed. I will let you know what happens when the cartridges arrive.
The pump is the square at the top with the return coming from the left. The check valve is the split line. The cold feed is the line at the bottom coming from the left and passing into the tank at the top. Sorry the diagram won't upload

Re: Cold Water Contamination with Hot Water

Sounds like a classic case of "cross-over". Replacing the mixing cartridge should resolve this issue. Also, you should consider optimizing your recirculation system by putting an on-demand pump, instead of a simple timer. The pump will only operate when you are actually using hot water and won't waste energy the way your existing pump does.

Re: Cold Water Contamination with Hot Water

Really appreciate the advice. I replaced the shower cartridge and control valve today and the problem is solved. I will look into the on demand setup. By the way, what is the recommendation for replacing a water heater. I have heard between 10 and 12 years?

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