Avoiding plumbing crossover in high-rises – tips!



Crossover occurs when hot water crosses, usually through a defective fixture, into the cold water piping or vice versa.


When the pressure in the hot and cold water lines differs, water will want to pass from high pressure to low. These hot and cold water systems are normally separate. However, mixing points – such as single lever faucets – connect hot a cold and provide a channel for crossover.


When hot water crosses into cold water lines the effect could be great enough to shatter a toilet bowl. When cold water crosses into hot water piping it can result in a lack of hot water. A typical resident complaint is a sudden change in temperature from hot to cold or vice versa after setting the temperature just right. Pinpointing the location of the defective fixture can be very difficult as it is within a suite, it may involve a resident’s shower, bathroom or kitchen tap and can be result of a resident’s maintenance practices. Symptoms of crossover may appear far from the suite where it originated – in suites above, below or beside the source.

Here are 6 valuable tips for finding and fixing crossover:

1. Check all suites on the same riser.

2. Replace the cartridges in Moen faucets. Older Moen faucets are a frequent cause of crossover. Replacement Moen cartridges are available free from plumbing suppliers.

3. Replace or modify designer Italian (European) faucets. Many require precisely equal hot and cold pressure and are not designed for the fluctuation present in high-rises. Replace them or modify them by installing spring- loaded check valves on supply lines.

4. Replace cheap handheld showerheads and advise residents on proper operation. Many of these feature an on/off button at the showerhead. Residents often turn on the hot and cold water at the tap and then press the button at the showerhead to enable the flow of water. When finished they release the button and leave the water on at the taps. The open valve(s) may be a crossover point.

5. Look for recent in-suite renovations. Sometimes, perhaps for pressure-testing, a plumber will create a temporary bridge between hot and cold water lines and forget to remove it.

6. Investigate further. To determine if neighbouring risers are affected take the following steps:

a. Isolate (turn off) the hot water riser.

b. Open cold water taps. The cold water should run properly.

c. Open hot taps. No water should flow. If water flows, you have crossover.

d. Start with tips 2 to 5.

If the building is a condominium, the condominium corporation should perform crossover investigations promptly and make basic repairs, such as cartridge replacement, at the corporation’s expense. This is vital to proper maintenance and helps to prevent escape of water that can affect the entire building.

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